EPA-600/2-77-1796
August 1977
Environmental Protection Technology Series
                          ION  OF MINERAL  QUALITY  OF
                             IRRIGATION  RETURN  FLOW
                      Volume  V. Detailed  Return Flow
                                   Salinity and  Nutrient
                                        Simulation  Model
                                Robert S. Kerr Environmental Research Laboratory
                                        Office of Research and Development
                                       U.S. Environmental Protection Agency
                                               Ada, Oklahoma 74820

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                RESEARCH REPORTING SERIES

Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology.  Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:

      1.  Environmental  Health-Effects Research
      2.  Environmental  Protection Technology
      3.  Ecological Research
      4.  Environmental  Monitoring
      5.  Socioeconomic Environmental Studies
      6.  Scientific and Technical Assessment Reports (STAR)
      7.  Interagency Energy-Environment Research and Development
      8.  "Special" Reports
      9.  Miscellaneous Reports

This report has  been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.

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                                            EPA-600/2-77-179e
                                            August  1977
        PREDICTION OF MINERAL QUALITY OF
             IRRIGATION RETURN FLOW
                    VOLUME V

        DETAILED RETURN FLOW SALINITY AND
            NUTRIENT SIMULATION MODEL
                       by

                Marvin J. Shaffer
                Richard W.  Ribbens
                Charles W.  Huntley
              Bureau of Reclamation
             Denver, Colorado  80225
                 EPA-IAG-D4-0371
                 Project Officer

                Arthur G. Hornsby
            Source Management Branch
Robert S.  Kerr Environmental Research Laboratory
              Ada, Oklahoma  74820
ROBERT S. KERR ENVIRONMENTAL RESEARCH LABORATORY
       OFFICE OF RESEARCH AND DEVELOPMENT
      U.S. ENVIRONMENTAL PROTECTION AGENCY
              ADA, OKLAHOMA  74820

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                            DISCLAIMER
This report has been reviewed by the Robert S. Kerr Environmental
Research Laboratory, U.S. Environmental Protection Agency, and
approved for publication.  Approval does not signify that the con-
tents necessarily reflect the views and policies of the U.S.
Environmental Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or recommendation
for use.
                                 11

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                               FOREWORD
     The Environmental Protection Agency was established to coordinate
administration of the major Federal programs designed to protect the
quality of our environment.

     An important part of the Agency's effort involves the search for
information about environmental problems, management techniques and
new technologies through which optimum use of the Nation's land and
water resources can be assured and the threat pollution poses to the
welfare of the American people can be minimized.

     EPA's Office of Research and Development conducts this search
through a nationwide network of research facilities.

     As one of these facilities, the Robert S. Kerr Environmental
Research Laboratory is responsible for the management of programs to:
(a) investigate the nature, transport, fate and management of pollutants
in groundwater; (b) develop and demonstrate methods for treating waste-
waters with soil and other natural systems; (c) develop and demonstrate
pollution control technologies for irrigation return flows; (d) develop
and demonstrate pollution control technologies for animal production
wastes;  (e) develop and demonstrate technologies to prevent, control
or abate pollution from the petroleum refining and petrochemical
industries; and (f) develop and demonstrate technologies to manage
pollution resulting from combinations of industrial wastewaters or
Industrial/municipal wastewaters.

     This report contributes to the knowledge essential if the EPA is
to meet the requirements of environmental laws that it establish and
enforce pollution control standards which are reasonable, cost effective
and provide adequate protection for the American public.
                                        William C. Galegar
                                        Director
                                        Robert S. Kerr Environmental
                                          Research Laboratory
                                   111

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                           PREFACE

     This report is one of a set which documents the development
and verification of a digital computer modeling effort to predict
the mineral quality changes in return flows occurring as a result
of irrigating agricultural lands.  The set consists of five separate
volumes under one general title as follows:

     "Prediction of Mineral Quality of Irrigation Return Flow"

         Volume I.    Summary Report and Verification

         Volume II.   Vernal Field Study

         Volume III.  Simulation Model of Conjunctive Use and Water
                      Quality for a River Basin System

         Volume IV.   Data Analysis Utility Programs

         Volume V.    Detailed Return Flow Salinity and Nutrient
                      Simulation Model

     This set of reports represents the culmination of an effort
started in May 1969 by an interagency agreement between the U.S.
Bureau of Reclamation and the Federal Water Pollution Control
Administration on a joint research proposal on the "Prediction
of Mineral Quality of Return Flow Water from Irrigated Land."
This research project has had three different project identifica-
tion numbers during the project period.  These numbers (13030 EH,
EPA-IAG-048-(D), and EPA-IAG-D4-0371) are given to avoid confusion
on the part of individuals who have previously tried to acquire
project reports for the earlier project numbers.
                                IV

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                               ABSTRACT
A return flow quality simulation model is described which models the
plant-soil-aquifer system from the soil surface to a tile or open drain.
Processes simulated include evapotranspiration, unsaturated and satu-
rated water flow, solution-precipitation of slightly soluble salts, ion
exchange, ion pairing, nitrogen transformations, crop uptake of nitro-
gen, and the movement and redistribution of salts and nutrients.

The dynamic non-steady-state model predicts the concentrations of calcium,
magnesium, sodium, ammonium, bicarbonate, carbonate, chloride, sulfate,
N03-N, and Urea-N contained in soil, aquifer, and drain waters. Concen-
trations of organic-N; exchangeable calcium, magnesium, sodium, and
ammonium; and gypsum are predicted within the soil and aquifer materials.

Users' manuals for each basic subprogram are included, and a sample
problem illustrates the use of the model.  Model output can serve as
input to the conjunctive use model described in Volume III; serve
as input to other models on a nodal or point source basis; or stand
alone depending on the type and scope of the particular study.

This report was submitted in fulfillment of project EPA-IAG-D4-0371
by the U.S. Bureau of Reclamation, Engineering and Research Center,
under the partial sponsorship of the Environmental Protection Agency.
Work was completed as of June 15, 1975.

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                            CONTENTS

Sections                                                          Page
Ifir TIT. -1 w... .1 IBI I!• Jl_ 11 • I                                                          ,	uBimiB-liLii ,,

     I     Conclusions  	          1

    II     Recommendations  	          2

   III     The Model  	          4

              Introduction  	          4
              Model Description - General  	          6
              Model Description - Irrigation
                Scheduling  	          6
              Model^Description - Unsaturated
                Flow  	          9
              Model Description - Drainout  	         10
              Model Description - Saturated Flow  	         11
              Model Description - Interface
                for Chemistry  	         12
              Model Description - Unsaturated
                Chemistry 	         12
              Model Description - Saturated
                Chemistry 	         13
              Model Description - Drain Effluent
                Prediction  	         14

   IV      Model Verification  	         16

    V      Model Strengths  and Weaknesses  	         24

   VI      Summary of Required Input Data  	         39

              Drainage  Design	         39
              Saturated Material Properties 	         39
              Unsaturated Material Properties  	         39
              Soils Analysis 	         40
              Crop Information 	         41
              Water Applications 	         41
              Fertilizer Information 	         41
              Irrigation Water Analysis 	         42
              Soils Temperature Data 	         42
              Soils Coefficients 	         42

  VII      Interfacing  with Conjunctive Use Model  	         43
                                  VII

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                      CONTENTS - Continued
Sections

 VIII      User's Manual - Overall Model 	

              Introduction 	
              Subprogram Linkage 	
              Bypass Options 	

                 Irrigation Scheduling 	
                 Unsaturated Flow and Unsaturated
                   Chemistry 	
                 Saturated Chemistry 	
                 Drain Effluent Prediction 	
                 Saturated Flow 	

              Tips on Model Application 	

                 Use of Bypass Options	
                 Intermediate Output 	
                 Printed Output Volume 	,
                 Accuracy Versus Computer Run Times ..
                 Conversion to Other Computer Systems

   IX      User's Manual - Irrigation Scheduling
             Program	

              Introduction 	
              Data Input Card Sequence and Data
                Limitations 	

     X     User's Manual - Unsaturated Flow Program .,

              Introduction	
              Data Deck Structure 	
              Node Spacing 	,
              Moisture Contents 	
              Unsaturated Flow Properties 	
              Initial Boundary Conditions 	,
              Consumptive Use Values	,
              Depleted Moisture Option 	
              Starting and Stopping Dates	
              Deficit Moisture 	
              Mass Balance 	
44

44
44
44

44

45
46
46
46

47

47
54
54
55
55
56

56

56

70

70
72
80
80
81
83
84
85
86
86
87
                                 Vlll

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                      CONTENTS - Continued
Sections
Page
              Restart of Problem 	        90
              Limitations 	        93
              Output 	        93
              Example of Subroutine PR0P 	        98
              Campbell's Method for Determining
                Unsaturated Flow Properties 	       103

    XI     User's Manual - Drainout Program 	       110

              Introduction 	       110
              Unit Numbers	       110
              Data Deck Structure	       Ill
              Design Inputs 	       117
              Selection of Drainage Case 	       119
              Application of Method 	       122
              Dynamic Equilibrium 	       123
              Deep Percolation Data 	       123
              Negative Starting Position	,	       124
              Restart of Problem 	       126
              Design Method 	       127
              Input Checks and Error Messages	       129
              Output 	       129

   XII     User's Manual - Interface for
             Chemistry Program 	       133

              Introduction 	       133
              Unit Numbers 	       134
              Data Deck Structure 	       135
              Tape Output Details 	  136

  XIII     User's Manual - Unsaturated
             Chemistry Program 	       139

              Introduction 	       139
              Card Groups 	       139
              Tape Inputs 	       153
              Card Outputs 	       156
              Tape Outputs 	       157
              Hints on Program Use 	       158
              Suggested Load Sequence 	       160
                                 IX

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                      CONTENTS - Continued
Sections

   XIV     User's Manual - Saturated Flow Program ....

              Introduction	
              Unit Numbers 	
              Data Deck Structure 	
              Standard Output 	
              Input/Output Options 	
              Grid Division and Geometry Modification
              Limitations and Error Messages 	
              Equations for Number of Nodes 	
              Logical Error Messages 	

    XV     User's Manual - Saturated Chemisry
             Program 	

              Introduction 	
              Unit Numbers	
              Data Deck Structure 	
              Tape Input 	
              Tape Output 	,	
              Limitations 	
              Output	
              Simulation of Unsaturated Zone 	

   XVI     User's Manual - Drain Effluent Prediction
             Program 	

              Introduction	
              Program Application	
              Quality of Leachate Water in Input
              Data from Saturated Chemistry
                Program is Input 	,
              Unit Numbers 	
              Data Deck Structure 	

  XVII     References 	

 XVIII     Appendix 	
161

161
161
162
167
168
169
169
171
173
177

177
179
180
192
194
196
196
197
199

199
199
199

200
201
205

225

228

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                        LIST OF FIGURES

Number                                                            Page

  1.       Typical Vertical Section Through
             Drainage F ield 	          7
  2.       Schematic Representation of Water
             Quality Model 	          8
  3.       Diagram of Field Application 	         19
  4.       Predicted and Observed Water Quality -
             Navajo Wash (Chemistry included) 	         20
  5.       Predicted and Observed Water Quality -
             Navajo Wash (Chemistry omitted) 	         23
  6.       Model Bypass Configuration No. 1  	         48
  7.       Model Bypass Configuration No. 2  	         49
  8.       Model Bypass Configuration No. 3  	         50
  9.       Model Bypass Configuration No. 4  	         51
 10.       Model Bypass Configuration No. 5  	         52
 11.       Model Bypass Configuration No. 6  	         53
 12.       Modeled System - Unsaturated Flow 	         71
 13.       Data Deck Structure - Unsaturated Flow
             Submodel 	         73
 14.       Punched Card Restart Deck - Unsaturated
             Flow Submodel 	         91
 15.       Unsaturated Flow Properties - Exponential
             Forms 	        100
 16.       Unsaturated Flow Properties	        102
 17.       Data Deck Structure - Drainout Submodel 	        112
 18.       Program Criteria to Select Drainage Case 	        121
 19.       Organization - Daily Moisture Tape	        125
 20.       Organization of Magnetic Tape Output -
             Drainout Submodel	        132
 21.       Card Groups in Unsaturated Chemistry
             Submodel 	        140
 22.       Data Deck Structure - Saturated Flow
             Submodel	        163
 23.       Boundary Conditions - Saturated Flow
             Submodel 	        165
 24.       Dimensionless Flow - Circular Tile Drains
             Below Horizontal Water Table 	        170
 25.       Segmented Flow Tube in Saturated Region 	        178
 26.       Data Deck Structure - Saturated Chemistry
             Submodel 	        181
 27.       Salt Inj ection from the Barrier 	        184
                                  XI

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                   LIST OF FIGURES - Continued

Number

 28.       Organization of Tape 2 Output from
             Unsaturated Chemistry Submodel	        193
 29.       Organization of Tape 16 Output from
             Saturated Chemistry Submodel 	        195
 30.       Data Deck Structure - Drain Effluent
             Prediction Submodel 	        203
                                XII

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                         LIST OF TABLES

Number                                                            Page

  1.       Initial Conditions South Montezuma
             Valley  (Towaoc Area)  	         17
  2.       Average Annual Water Application Sequence 	         18
  3.       Present Observed and Predicted Conditions 	
             (South Montezuma Area)	         21
  4.       Present Observed and Predicted Conditions 	         22
  5.       General Model 	         25
  6.       Irrigation Scheduling Submodel 	         29
  7.       Chemical Equilibria Submodel 	         30
  8.       Nitrogen Transformation Submodel 	         31
  9.       Nitrogen Uptake Submodel 	         32
 10.       Salt Movement Submodel  	         33
 11.       Unsaturated Flow Submodel  	         34
 12.       Drainout Submodel 	         35
 13.       Saturated Flow Submodel 	         36
 14.       Saturated Chemistry Submodel 	         37
 15.       Drain Effluent Submodel 	         38
 16.       Drain Effluent Prediction Program 	         216
 17.       Drain Effluent Prediction Program 	         217
                                  Xlll

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                         ACKNOWLEDGEMENTS
The foresight of Mr. John T. Maletic in supporting and promoting
modeling efforts from the earliest stages made a significant impact
on the rapid advances seen in this and other simulation models.

The pioneering efforts of Dr. Gordon R. Dutt in the development of
the chemical equilibria subprograms and his assistance with other
portions of the model are gratefully acknowledged.

Dr. Arthur W. Warrick and Mr. William J. Moore contributed the basic
portions of the Unsaturated Flow Program.

Messrs. Errol Jensen and Robert Julian of the Durango Planning Field
Division assisted in the model field verification study in the South
Montezuma Valley, Colorado area.

Messrs. Norman A. Roth, Roger W. Falkenstein, and Gary C. Shulstad
of the Missouri-Souris Projects Office developed the basic input
data used in the sample model runs contained in the Appendix.

The major sponsorship of this work was provided by the Mid-Pacific
Region and Water Quality Office of the U.S. Bureau of Reclamation.
                                 xiv

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                           SECTION I

                          CONCLUSIONS

The simulation model described in this volume is a highly flexible,
sophisticated tool which can be used to predict the effects of initial
soil and aquifer conditions, cultural practices, input water quality,
and other factors on water and soil chemistries throughout the plant-
soil-aquifer system.  Output can be used as input to other models
which consider the combined effects of several point sources on stream
quality in a river basin or subbasin.

The model also has many stand-alone applications such as predictions
involving the reclamation of saline and sodic soils, drain spacing
design, salt and nutrient pollution studies on soils and aquifers,
consumptive use predictions, and irrigation scheduling.

Potential model applications (those which would require additional
programing or modifications) include prediction of crop response to
salinity, optimization of nitrogen fertilization schedules, irrigation
scheduling (including unsaturated flow and salinity), and prediction
of additional quality parameters such as pesticides, phosphates, and
trace elements.

The flexibility built into the model allows the user to select the
degree of modeling sophistication needed for a particular application.
This can range from rough approximations to complete usage of the
model's capabilities.

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                             SECTION II

                           RECOMMENDATIONS

1.  The total simulation capabilities of this model should be utilized
only when a maximal effort is indicated by the data and type of applica-
tion.  For reconnaissance and survey applications, numerous submodel
bypass options are available to the user.

2.  Although the primary outputs from the model are flow and quality
predictions associated with a tile or open drain, other model applica-
tions involving predictions within the plant-soil-aquifer system are
extremely useful.

3.  This model (Volume V) should be interfaced with the conjunctive
use model (Volume III) when flow and quality predictions are wanted
for a river basin or subbasin (e.g. more than one node), when more
flow and chemistry detail is wanted in the unsaturated and saturated
zones, or when predictions of nitrogen transformations are desired.

4.  Additional research is needed to develop and refine methodology
to select the input data used in this and other simulation models.

5.  Additional field verification must be undertaken on this and
other models before they can be applied with a high degree of confi-
dence.  The current confidence level of this model can be rated as
moderate with the accuracy of field predictions (areas on the order
of thousands of acres) appearing to be within about 10 to 15 percent
of observed data.  Future verification studies could raise or lower
this figure.

6.  The user should read and thoroughly understand the basic meth-
odology associated with the model before applying it.

7.  An important application of this model should be its use as a
basis to develop more sophisticated simulation tools.

8.  Although this model can (and has) been converted to other com-
puter systems, consideration should be given to utilization of the
Bureau of Reclamation CYBER 74-28 system via remote terminals.

9.  This model represents a "first generation" attempt at modeling
the plant-soil-aquifer system.  A "second generation" model can and
should be developed at an early date.  The following features should
be incorporated into this more advanced modeling tool:

   a.  Unsaturated and saturated flow in three dimensions.

   b.  Multiple soil horizons in the flow submodels.

                                   2

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c.  A moving water table in the unsaturated flow submodel.

d.  An improved inorganic chemistry submodel which incorporates
additional ion pairs and solid phases under certain conditions.

e.  An improved denitrification submodel.

f.  An improved plant uptake of nitrogen submodel including a
variable root distribution and improved uptake functions.

g.  Additional submodeling to allow simulation of acid soil
chemical reactions.

h.  Temperature effects in the inorganic chemistry submodel.

i.  Generalization of certain reaction rate equations in
nitrogen transformation submodel.

j.  Addition of submodels which simulate phosphorous, pesticide,
and trace element reactions and movement in soils.

k.  Direct modeling of mechanical dispersion.

1.  Fertilizer scheduling capability.

m.  A  submodel simulating crop response to salinity.

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                          SECTION III

                           THE MODEL

INTRODUCTION

During the past several years there has been a growing awareness
of the environmental problems created by man's present and past
activities.  Prominent are those concerning water quality.  When-
ever water is withdrawn from a natural supply and used or consumed,
its characteristics are changed.  In particular, irrigation water
usually experiences significant alterations in passing through the
soil system before it is returned to the surface, either through
natural or artificial drainage pathways.

The nature of these alterations depends on many interrelated char-
acteristics of the soil-water system.  Included are physical prop-
erties governing percolation of water through a porous media and
chemical characteristics which determine the nature of the chemical
pathways.  Both are essentially beyond man's control.  In contrast,
the design of artificial drainage systems, selection of crop types,
and fertilization and irrigation practices are largely within man's
control.

Viewed as a whole, the soil-water system is quite complex.  In order
to understand the processes involved, workers have traditionally
dissected the system for closer inspection.  Thus, the agronomist
is mainly concerned with crop productivity and factors affecting it
and is only indirectly concerned with movement of water beyond the
root zone.  In contrast, the drainage engineer is primarily concerned
with estimates of deep percolation and the need to keep the water
table below the root zone.  In reality, activities in both saturated
and unsaturated zones are related.  Changes in cultural and irri-
gation practices affect the entire system to some degree, although
transformations in time and space may mask the cause-effect rela-
tionship.  However, in order to evaluate these relationships, it is
essential that the individual components again be interfaced and
integrated.

When new or former dryland farms are brought under irrigation, it
is desirable to forecast the quality of the return flows.  If sim-
ilar areas have already been developed, their performance can be
used to make this estimate.  Where this is not possible, extrapola-
tion from dissimilar areas can lead to gross errors.  As an alter-
native, a simulation model of the soil-water system, based on the
essential physical processes in it, can aid in predicting return
flow quality.

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The estimated results from a simulation of the  system  should  not be
considered or represented as exact.  There are  three major  sources
of uncertainty:

   a.  Model approximations and assumptions.  These are made  to
   simplify the model.  They may be dictated by a  lack of basic
   knowledge, by a  lack of required data, or by the accuracy  of
   the results required.

   b.  Field variability.  The parameters of a  natural system may
   possess significant spatial and temporal variations.  Costs of
   data collections generally prevent acquisition  of sufficient infor-
   mation to define it completely.  Subjective  estimates and  intuitive
   judgment are often employed to keep costs down.

   c.  Stochastic processes.  For example, rainfall, solar radia-
   tion, and temperature processes, are not completely understood
   and apparently include random components.  These affect plant
   evapotranspiration and growth processes, as  well as other por-
   tions of the system.

Despite these uncertainties, a simulation model can be used to make
the most of the available data.  It becomes another tool available to
the decisionmaker in assessing the impact of an irrigation project.

The detailed return flow quality simulation model  described in this
volume was developed over a period of about 7 years and has had
several contributors  (see acknowledgements).  The  model simulates
chemical and physical processes associated with agricultural  lands
drained by subsurface tile drainage systems.  The  simulation begins
with field applications of water, salts, and nutrients (nitrogen)
and ends with predictions of flow and water quality from the drains.
In addition, the model can be applied to areas  with surface drainage
systems and can provide predictions of quality  and flow parameters
at various additional points within the plant-soil-aquifer system.
The background, theory and development of the various subprograms
within the model have been published elsewhere  and need not be
repeated here.

Numerous references are included in the brief descriptions of each
subprogram.  The reader is advised to thoroughly familiarize himself
with these materials before attempting to utilize  the model.

Detailed user's manuals and a sample problem have  been included to
facilitate application of the model.

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MODEL DESCRIPTION - GENERAL

Consider a typical vertical section through a drainage field as shown
in Figure 1.  Water is applied at the land surface, either as irriga-
tion or precipitation.  A portion evaporates or becomes surface run-
off.  The remainder infiltrates the soil system and becomes available
for use by the plants or crops.  In addition to evapotranspiration,
there is nitrogen uptake by the plants.  As water percolates verti-
cally to the water table, chemical reactions occur.  Upon reaching
the water table, flow takes place under saturated conditions, even-
tually reaching the drains.  Chemistry changes continue to occur in
this saturated system.

This brief description leads to the schematic representation of the
water quality model as shown in Figure 2.  Each program part or block
is identified with a major component of the physical system.  The
conceptual model was translated to mathematical notation and programed
in Fortran IV for solution by a large, third-generation computer.  All
programs are operational on the Control Data Corporation CYBER 74-28
computer located at the USER Engineering and Research Center in Denver,
Colorado.  A brief description of each block follows.

MODEL DESCRIPTION - IRRIGATION SCHEDULING

The timing and amounts of irrigation are required for input to the
Unsaturated Flow Program.  Deep percolation volumes are needed by
the Drainout Program.  This information may be developed subjectively
based on past experience, by consideration of cultural practices in
similar areas, or by using manual or automatic irrigation scheduling
techniques.  The latter is desirable where rainfall contributes sig-
nificantly in meeting plant requirements.

The philosophy involved in irrigation scheduling is to keep a daily
account of soil moisture in the root zone of the crop.  This is accom-
plished by considering major inputs (irrigation and precipitation) and
withdrawals (crop evapotranspiration and deep percolation).  At pres-
ent, a separate program is used.  Since the simple bookkeeping pro-
cedures used in this program require estimates of deep percolation
losses and ignore possible contributions of water to the root zone
by capillary flow, it is anticipated that the scheduling techniques
will be incorporated in the Unsaturated Flow Program.  This will
avoid duplication of elements common to both programs, avoid incom-
patibilities,  and speed the scheduling process.

Crop evapotranspiration is computed using the Jensen-Haise method
(7, 8).  Evapotranspiration is increased for 3 days following a rain-
fall or irrigation based on a procedure used by Jensen (8, p. 956).
This curve relates evapotranspiration at various growth stages to

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  Land surface
Crops  (evapotranspiration or consumptive use)
                                         Bounding streamline
                                                                                  e>
                                                                                  LU
                                               CO
                        Impermeable barrier
FIGURE  I.    TYPICAL  VERTICAL  SECTION  THROUGH  DRAINAGE  FIELD

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DRAINOUT
                  IRRIGATION
                 SCHEDULING
UNSATURATED
   FLOW
                  SATURATED
                    FLOW
INTERFACE
   FOR
CHEMISTRY
                                      UNSATURATED
                                        CHEMISTRY
                      SATURATED
                      CHEMISTRY
                                         DRAIN
                                        EFFLUENT
                                       PREDICTION
    FIGURE 2.  SCHEMATIC  REPRESENTATION
           OF WATER  QUALITY  MODEL

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the estimated potential  evapotranspiration.   If soil  moisture is
depleted below the allowable  depletion  percentage,  evapotranspiration
is reduced linearly, going  to zero when all  soil moisture  is  used.

In addition to irrigation scheduling  information, average  evapotran-
spiration rates on a semimonthly  basis  are computed for  input to  the
Unsaturated Flow Program.   Rainfall also is  accumulated  on a  semi-
monthly basis and applied on  the  15th and last  day  of the  month.

MODEL DESCRIPTION - UNSATURATED FLOW

The unsaturated flow submodel describes the  infiltration,  redistri-
bution drainage, and plant  root extraction of soil  moisture by a
growing crop  (5, pp. 8-21).   Darcy's  Law is  assumed to apply  in
relating velocities to total  hydraulic  heads.   Two  modifications  are
made:

   a.  The permeability  (hydraulic conductivity)  is taken  as  a func-
   tion of moisture content.   This accounts  for the reduced area
   available  for flow at lower moisture contents.

   b.  The pressure (tension)  head is taken  as  a function  of  mois-
   ture content.  This accounts for the fact  that different forces
   predominate at different moisture  levels.  Thus  at  high levels
   gravity is most important  while at low levels capillary or molec-
   ular forces have greatest  effect.

Hysteresis in both the tension head and conductivity  functions is
ignored.  Multiphase flow (simultaneous movement of air, water vapor,
and water) is not treated.  Flow  is assumed  to  be independent  of
quality, although the chemical processes  depend on  the flow.

Since both the conductivity and head  are  highly nonlinear  with mois-
ture content, solution of the flow equation  is  accomplished using
numerical methods.  An implicit finite  difference scheme is employed
and flow is treated as one dimensional  in the vertical direction.

Water applications are applied on the proper  date and  represent "effec-
tive" values.  Thus, surface  runoff and evaporation from depression
storage are subtracted from the total amounts.   Withdrawal of water by
the plants is accomplished on a macroscopic basis using a  "sink" term
in the governing flow equation.  Thus,  water  is  extracted  continuously
from the land surface to the  bottom of  the root  zone  in proportion to
the root distribution.  Details of flow to individual  roots are not
considered.  Plant evapotranspiration is  estimated  by  the  Jensen-
Haise method utilized in the  Irrigation Scheduling  Program or  by using
the Blaney-Criddle method.  At present,  root  distributions are taken
as constant with time and are  chosen  to reflect  the mature growth stage.

-------
Water to meet the  specified  evapotranspiration  is  removed  node  by node
as long as moisture levels are above a  specific  lower  limit, usually
taken as the wilting point.   If  levels  fall below  this  limit at a node
no water will be withdrawn from  that node  and the  evapotranspiration is
reduced.  The reduction  is accumulated  and listed  as the "deficit mois-
ture."  No consideration is  made  for effects due to permanent wilting.
When water contents again go above the  wilting point,  the  plants use
water at the specified evapotranspiration  rates.   Effects  of salinity
on evapotranspiration are also ignored.

The lower boundary of the one-dimensional  column is taken  as the water
table, which for purposes of the  Unsaturated Flow  Program  is taken as
the mean annual location of  the water table.  Hydraulically it  is
treated as a zero  pressure surface maintained at the saturation mois-
ture content.  The upper boundary is treated as a  specified head bound-
ary when water stands on the surface after an irrigation and as a zero
flow boundary when all water from a surface application has infiltrated.

Moisture contents  and water  movements are  then used as  inputs,  via
the interface program, to the Unsaturated  Chemistry Program.  Water
crossing the lower or water  table boundary also acts as input to the
Drainout and Saturated Flow  Programs.

MODEL DESCRIPTION  - DRAINOUT

The quantity of water crossing the water table during a given day,  as
computed by the Unsaturated  Flow  Program,  is used  to calculate  the
position of the water table  and  the drain  discharge as a function of
time.  Standard Bureau methods for drainage system design  are used.
These are described by Dumm  (1,2,3).

Basically, the water table shape  is chosen as a fourth-degree parab-
ola.  Daily increments of flow across the  water table are  used  in
conjunction with the specific yield to  compute instantaneous rises
(if water moves from the unsaturated to saturated  system)  or instan-
taneous declines (if water moves  from the  saturated to unsaturated
system by capillary flow).   Equations describing the flow  of water
through the saturated system  to parallel circular  drains are then
used to compute drain discharge and the fall of the water  table due
to drainout during the day.

Since the formulations are based  on the Dupuit-Forchheimer assumptions
which treat flow as parallel  and  neglect the effects of convergence,
corrections for the depth of  flow are made.  Hooghoudt's equivalent
depth is employed  for this purpose.  Approximate equations developed
by Moody(ll)  are used to simplify the program.

Discharge values,   computed on a daily basis, are accumulated to yield
monthly and yearly values.   By considering initial and final water
                                  10

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table positions for each year, changes in storage during the year may
be computed.  Since the amount of water crossing the water table is
known, application of a mass balance equation permits a semi-independent
determination of the annual drain discharge.  If this differs signifi-
cantly from that computed using the drainout method, all daily discharge
values are adjusted to yield mass balance.  This approach is used
because the discharge formulas are based on the first few terms of an
infinite series and the constants are increased for design purposes
(6, Eq 54, p. 41).  Since the adjustment coefficients may differ from
year to year, daily discharge values may exhibit discontinuities
between years.

The resultant adjusted monthly discharge values are then used as input
to the combining or drain effluent programs.

MODEL DESCRIPTION - SATURATED FLOW

The total amount of deep percolation computed by the unsaturated flow
program is converted to an average annual rate for input to the satu-
rated flow program.  Using the geometry of the drainage system, a
steady-state potential theory solution is employed to define stream
paths or lines to the drain  (12, Section 2).  These solutions remove
the limitations imposed by the Dupuit-Forchheimer assumptions.

A number of stream tubes may be defined to represent the two-
dimensional flow system.  Since an average annual seepage rate is
used, a mean or average stream tube system results.

Because the equations defining the potential and stream functions are
in terms of infinite series involving trigonometric, hyperbolic, and
exponential functions, a node system is superimposed over the drain-
age system.  Stream functions are computed at the nodes and required
values found by linear interpolation.  The corresponding potentials
are then computed.  With streamlines located at the hydraulic center
of each tube and the potentials known, Darcy's Law is employed to
calculate velocities of flow between adjacent points on the stream-
line.  Using the known distances and porosities, these velocities
are converted to travel times.  Integrating or summing the travel
times then yields the total time required for water crossing the water
table to arrive at the drains assuming piston displacement.

The water table position is also computed and the total volume of aqui-
fer contributing to one drain is found by numerical integration.  This
volume is then distributed between individual tubes using the computed
travel times as the basis.

The pore volumes are used for input to the saturated chemistry pro-
grams and are necessary in calculating the soil mass and associated
                                  11

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pore volumes in the control volumes used for calculating chemical
changes.  Each stream tube is treated independently in the saturated
chemistry program and the results combined in the drain effluent pro-
gram.  This combining is based on the relative travel times for piston
displacement in each tube.

MODEL DESCRIPTION - INTERFACE FOR CHEMISTRY

Moisture contents and movements from the unsaturated flow program
are computed at the nodes used in the finite difference equations.
In contrast, the unsaturated chemistry programs use a soil segment
concept in which each segment is assumed to possess homogeneous char-
acteristics.  Because the segment centers and nodes of the unsat-
urated system may not coincide or be identical in number, an inter-
face program is necessary.  This program computes average moisture
contents in each soil segment as well as movements of water between
soil segments for a given time interval.

MODEL DESCRIPTION - UNSATURATED CHEMISTRY

The Unsaturated Chemistry Program simulates a number of important
biological, chemical, and physical processes (5, pp. 21-79).  These
include:

   a.  Nitrogen transformations, including the hydrolysis of urea,
   mineralization-immobilization of organic-N and ammonium, nitri-
   fication of ammonium, and immobilization of nitrate.  Because
   the rates of these transformations are slow (on the order of days
   or weeks), a kinetic approach is used.

   b.  Salt or inorganic chemistry, including ion exchange, solution-
   precipitation of slightly soluble salts, the formation of undis-
   sociated ion pairs, and the bicarbonate buffer system.  Since
   reaction times are rapid (on the order of seconds or minutes),
   chemical equilibrium conditions are assumed.

   c.  Unsaturated movement and redistribution of soluble constituents.

   d.  Crop uptake of nitrogen.

The nitrogen rate equations were developed by applying system analysis
concepts to define and limit the system and to establish pertinent
variables and reaction pathways.  Equations based on these variables
were derived using multiple-regression analysis, reaction rate theory,
and statistical thermodynamics(5,13,14).  Variables include ammonium,
nitrate, organic-N, and urea concentrations; temperatures; carbon-
nitrogen ratios; ionic strength; and soil moisture contents.
                                   12

-------
Chemical reactions included  in the  salt  (inorganic)  chemistry portion
are the dissolution and precipitation  of gypsum(5,16,17,21) and calcium
carbonate(5,21) undissociated ion pair reactions  for calcium sulfate
and magnesium sulfate(5,16,17,21),  calcium-magnesium ion  exchange(5,17),
calcium-sodium exchange(5,21), sodium-ammonium  exchange(S), and
pCOa - Ca++ - HCOa  interactions(5).   Constituents presently considered
in this portion of the model are nitrate,  ammonium,  calcium, sodium,
magnesium, bicarbonate, chloride, carbonate, and  sulfate.

Solutes contained in the  soil water are  assumed to move with the
water into and/or from adjacent segments (5, p. 23).  The volume of
water which moves and the mean water content of each segment (cell)
over a time step are inputed from the  Unsaturated Flow Model via the
Interface Program.  Because  each cell  is spatially homogeneous,
solutes transferred into  a segment  or  cell are  mixed with those
already in the cell.*  This  transfer may be either in an upward or
downward direction.  After each mixing operation, the soil solution
phase is equilibrated with the solid and exchangeable phases.  Since
a number of cells, usually 10 or more, are used,  this numerical tech-
nique tends to simulate physical or mechanical  dispersion.  This type
of dispersion arises from tortuosity of  the flow  paths whereby flow
splits and branches in going around individual  soil  particles.  Molec-
ular diffusion resulting  from molecular  energy  movements  is ignored
and is generally significant only when little or  no  water movement
occurs.

MODEL DESCRIPTION - SATURATED CHEMISTRY

In addition to the quantity  and quality  of leachate  water predicted
by the Unsaturated Chemistry Program,  the Saturated  Chemistry Program
accepts the stream tube volumes determined in the Saturated Flow Pro-
gram as input.  Each tube is treated independently and is subdivided
into a number of segments of equal  volume.  Leachate water is accu-
mulated until it equals the  pore volume  in a single  segment.  It is
then assumed to move by piston displacement through  successive seg-
ments until it reaches the drain. (4)   After each  displacement, the
solution phase is equilibrated with the  solid and exchangeable phases.

Lateral mixing between tubes and  longitudinal mixing in adjacent seg-
ments is ignored.  Thus,  lateral dispersion and diffusion are ignored.
For saturated systems this is considered realistic.
* This technique applies  only  to the unsaturated  zone.  A different
procedure is used  in  the  saturated  region.
                                    13

-------
Chemical transformations are computed after the slug of water enters
each segment.  They are identical to those in the salt chemistry por-
tion of the Unsaturated Chemistry Program except that denitrification
is simulated as the deep percolation water crosses into the saturated
zone.  Denitrification is assumed to occur at a rate which is temper-
ature dependent but independent of substrate (i.e., N03) concentrations
or zero order above a "saturation" level.  This level has not been
well defined but probably is on the order of a fraction to a few ppm
N03-N.  Below this level, the reaction rate becomes first order and
decreases as the N03-N concentration diminishes.

Initially, the entire saturated zone is considered as homogeneous.*
Laboratory analyses of soil samples in this zone are used to define
initial conditions.  If more than one sample is available, analyses
may be averaged or a single typical analysis used.

As each slug of water enters the segment adjacent to the water table,
the slug contained in the segment adjacent to the drain is considered
totally displaced.  The quality of water discharging from the given
stream tube is now that of the water in the segment adjacent to the
drain after all reactions have occurred.  It remains at this quality
until another slug enters the tube at the water table.  Individual
tubes are combined in the Drain Effluent Prediction Program.

Although the saturated system is initially homogeneous, the passage
of water down individual tubes soon produces heterogeneous conditions.
As each slug moves from segment to segment, its quality changes.  The
chemistry of the soil complex also undergoes corresponding changes.
As more tubes and segments are used, the continuous two-dimensional
system is more closely approximated.

MODEL DESCRIPTION - DRAIN EFFLUENT PREDICTION

The Drain Effluent Prediction Program accepts as input the quality
of each slug discharging into the drain from individual tubes, the
mean travel times for piston displacement, and the monthly volume
of drain discharge.  Travel times are used to calculate arrival times
of each slug at the drain on a tube-by-tube basis.  Using these times,
the resultant quality of the drain effluent is obtained by combining
the appropriate slugs from individual tubes.  This gives a varying
* The program will accept a different soil analysis for each segment.
However, because stream tubes curve and segments are of different
lengths, a considerable effort is required to use analyses by depth.
It is anticipated that future program additions will automate this
task.
                                   14

-------
drain effluent quality under steady discharge.  The monthly volumes
are then used to convert these results to the varying discharge pat-
tern with the corresponding monthly qualities.  The accumulated salt
load out of the drain and the rate of removal are also computed.

All results are given for individual constituents and for the total
load.  The total load is taken as the sum of the individual parameters
and approximates the total dissolved solids.  Constituents presently
considered are nitrate-nitrogen, ammonia-nitrogen, calcium, sodium,
magnesium, bicarbonate, chloride, carbonate, and sulfate.  Output
may include cathode ray tube plots, printed listings, and punched
cards.  Results are on a "per-acre" basis.  The assumption is made
that no chemical reactions occur after the mixing process in the
drain.
                                   15

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                           SECTION IV

                       MODEL VERIFICATION

Verifications of the various subprograms within the model are included
in the literature pertaining to each program.  Appropriate sections
describing each subprogram should be consulted for specific citations,

Verification of the model as applied to the field situation has been
obtained for an irrigated area in southwestern Colorado.  An area of
about 2,200 acres has been irrigated for about 75 years.  Soil samples
from an adjacent unirrigated area were utilized to estimate the ini-
tial soil conditions.  The soil analyses from two sites were weighted
with depth to obtain mean soils data.  These data appear in Table 1.
Profile B3 represents soils closest to the associated stream (Navajo
Wash) while profile B2 represents conditions farther from the stream.
Selection of sampling sites was based entirely on the experience of
field personnel.

Model bypass configuration No. 1 (see Section VIII, Figure 6) was
selected with the Irrigation Scheduling Program bypassed.  An annual
average irrigation and precipitation input sequence was derived for
the simulation period (Table 2).  This sequence was applied to the
irrigated area for the 75-year period.

A typical cross section through the irrigated area is shown in
Figure 3.  The diagram includes the five stream tubes used in the
simulation together with mean travel times for each.  Note the rela-
tively high travel times for flow through this aquifer.

Predicted and observed values for constituent and TDS concentrations
with time are given in Figure 4.  Predicted and observed mean soil
profile data after about 75 years of irrigation appear in Table 3.
These soil profiles were selected in approximately the same relative
locations as the input profiles.  The agreement between prediction
and observation was on the average within about 8 percent for soil
water quality and about 12 percent for stream quality.  More detail
in the simulation such as additional soil profiles, layering with
depth, unsaturated flow and chemistry, additional ion pairs, and
better estimates of C02 partial pressure would probably improve the
agreement.

There has been some difference of opinion and confusion concerning
the importance of including the chemical reactions in field simula-
tions. (23, 24)  To test the significance of the chemistry in this
study, computer runs were repeated in all respects except that the
subroutines which simulate the chemistry were bypassed.  In effect,
                                  16

-------
        Table 1.  INITIAL CONDITIONS
           South Montezuma Valley
                (Towaoc Area)
Soil profile        B2        B3
Ca++
Na+
Mg++
HC03~
C03~
Cl"
80,,=

SUMS

24
52
57
1
0
8
118
260

8,369
29
110
51
2
0
32
145
369

11,940
Meq/L
Meq/L
Meq/L
Meq/L
Meq/L
Meq/L
Meq/L
Meq/L

Mg/L
                        17

-------
Table 2.  AVERAGE ANNUAL WATER APPLICATION SEQUENCE
Application
No.
Depth



meq/L





(Cm)
Ca++
Mg**
Na+

HC03-
C03"
S0^s
ci-
N03~
1
1.37
0.75
0.09
0.04

0.39
0.00
0.60
0.01
0.00
2
0.33
13.26
9.68
1.86

10.49
0.00
7.18
1.44
0.05
3
1.60
22.77
5.54
4.13

20.42
0.00
9.48
3.47
0.08
4
1.14
23.85
5.91
4.41

21.41
0.00
9.76
3.75
0.09
5
1.02
23.85
5.13
4.23

20.75
0.00
9.58
3.57
0.08
6
1.27
20.84
4.98
3.66

17.75
0.00
9.01
3.09
0.08
7
0.51
19.34
4.51
3.29

16.53
0.00
8.63
2.82
0.07
8
0.38
19.24
4.60
3.38

16.90
0.00
8.73
2.82
0.07
9
0.13
13.05
2.63
1.78

9.95
0.00
7.14
1.41
0.05

-------
                     1800 Ft.-
        -Land  surface
                                          Mean travel time
                                             59 Yrs.
FIGURE  3.  DIAGRAM  OF  FIELD  APPLICATION

-------
  1000 -
  (ppm)
  1000 -
   900 -
   800 -
   700 -
   600 -
   500 -
   400 -
   300 -
   200 -
   100 -
                                                 IDS •
                                                 S0 = •
                                               Mg-n- x
                                             Predicted-x-
           10    20
     30   40    50
       TIME (YEARS)
                                     60
                                                 Na+
                                                    o
                       TIME (YEARS)
                               HCOj a
           10
20
30
40
i
50
                                      60
                70
 I
80
                       TIME (YEARS)
FIGURE 4. PREDICTED  AND OBSERVED WATER QUALITY
        NAVAJO  WASH  (CHEMISTRY  INCLUDED)
                            20

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        Table 3.  PRESENT OBSERVED  AND  PREDICTED  CONDITIONS
                       (South Montezuma  Area)
                   M2  (near  Wash)        M3  (farther  from Wash)
Soil profile    Observed   Predicted     Observed     Predicted
Ca++ 25
Na+* 50
Mg"1"1" 29
HCOa" 2
co 3- o
Cl~ 3
S0k~ 97
206
SUMS
6,885
28
27
43
3
0
4
89
194

6,298
23
61
59
2
0
10
131
286

9,342
27
49
60
2
0
7
123
268

8,668
Meq/L
Meq/L
Meq/L
Meq/L
Meq/L
Meq/L
Meq/L
Meq/L

Mg/L
Percent error        8.5                        7.2
   Mean
percent error                     7.9
the applied waters were concentrated according to the consumptive
use and routed through the system.  Initial conditions were identical
to those used previously.

Predicted and observed soil profile data after 75 years are given in
Table 4.  The prediction error increased from 8.5 to 48.2 percent in
the soil closer to Navajo Wash and from 7.2 to 20.9 percent at the
more distant soil location.  Since the soils closest to the drain are
more highly leached, the conclusion can be made that the chemical reac-
tions become increasingly more important as leaching progresses.

However, even in the soils more distant from the discharge point,
the improvement in predictive capability would easily demand inclusion
of the chemistry in the simulation.
                                  21

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          Table 4.  PRESENT OBSERVED AND PREDICTED CONDITIONS
                          South Montezuma Area
                     (Chemical Reactions Bypassed)
                   M2 (near wash)
Soil profile   Observed   Predicted*
        M5 (farther from wash)
        Observed   Predicted*
CA-1"1"
Na+
Mg++
HC03
CO 3=
Cl
so»r

SUMS

25
50
29
2
0
3
97
206

6,885
20
15
17
13
0
4
35
104

3,566
23
61
59
2
0
10
131
286

9,342
25
43
48
6
0
7
98
227

7,388
Meq/L
Meq/L
Meq/L
Meq/L
Meq/L
Meq/L
Meq/L
Meq/L

Mg/L
                                              20.9
   Mean
percent error
34.6
Predicted and observed data for water quality in Navajo Wash with the
chemistry omitted from the calculations appear in Figure 5.  These
results indicate the prediction error increased from about 12 percent
without the chemistry considered to about 28 percent without the chem-
istry after 70-75 years of irrigation.

A comparison of the predicted curves in Figure 5 with those in Figure 4
shows the Figure 5 TDS predictions are initially, high across the
Figure 4 TDS curve, and are low in the 70-75 year period.  This empha-
sizes the variable conclusions which can be drawn concerning the impor-
tance of the chemical reactions.  It appears from this analysis that
the chemistry is extremely important in most cases and should be
included in the simulation.
                                   22

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  (ppm)
  4000 -i
  3000 H
  2000 H
  1000
                -IDS
           10
20
                       TIME (YEARS)
30    40    50
  TIME  (YEARS)
                                 TDS_«
                                 so;«
                                 Mg++X
                                 No+A
                                 cro
                                           70
                                                80
  (ppm)
  1000 -
   900 -
   800 -
   700 -
  600 -
   500 -
   400 -
   300 -
   200 -
   100 -
           IO
—I	1	1	1—
 20    30    40    50
       TIME  (YEARS)
                                     60
                                           70
                          80
FIGURE 5.  PREDICTED  AND  OBSERVED  WATER QUALITY
        NAVAJO  WASH  (CHEMISTRY   OMITTED)
                            23

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                            SECTION V

                 MODEL STRENGTHS AND WEAKNESSES

The model contains numerous strong and weak points which may not be
readily apparent from the model descriptions and supporting docu-
mentation.  The following set of tables contains 2 summary of major
strengths and weaknesses associated with the model.  In addition,
comments are provided which should help clarify certain points.  The
summary should not be considered an exhaustive treatise on the subject,
but merely an aid to better understanding the basic capabilities and
limitations of the model.
                                   24

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Table 5.  GENERAL MODEL
         Strengths
        Weaknesses
            Comments
The model is not directly
tied to a specific irriga-
tion system and can be used
for almost any system by
using the programs properly
and interpreting the data
inputs properly.
The  model  must  be  applied
to each  specific situation
encountered.  Theoretically,
any  change in inputs  re-
quires a separate  analysis.
 Model is built on a modular
 basis using subroutines and
 the Fortran IV programing
 language.  It is easily
 expanded.
Different systems such as
furrow and drip irrigation
must be approximated and
the assumptions "lived"
with.
Extrapolation to large areas
involves the problem of field
variability.  It may be uneco-
nomical to collect the neces-
sary field data and make
model runs.
There are already a large
number of subroutines and
programs in the model.
Knowledge of programing is
also required.

The model is relatively
complicated and expensive to
run.  Data requirements are
considered excessive by some
individuals.
Specifics can be added  to
remove limitations and  assump-
tions.  Basic irrigation system
design is tied into the model by
efficiencies which are  input to
the irrigation scheduling sub-
model.  Efficiency also relates
cultural practices, crop and
soil types, climatic conditions,
and land slopes, etc.

The effect of areal variability
and the sensitivity of  model
results to it is an item needing
further research.  Practically,
results are more sensitive to
some inputs than to others.  How-
ever, relative sensitivity can
change from problem to problem.

Special features of Fortran com-
pilers that are only available
at one computer center have gen-
erally been avoided.
                                                               Efforts to include items not
                                                               presently included will tend to
                                                               further complicate the model.

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         Table  5.   (continued) GENERAL MODEL
                  Strengths
                                 Weaknesses
                                                        Comments
to
Ox
         The model simulates many
         important physical and
         chemical processes which
         have been identified
         over the years and
         expressed in equation
         form.
         The following quality para-
         meters are included in  the
         model:  Ca++, Mg++, Na"1",
         NH.
NO,
co3, ci,
         SO^, urea, organic-N,
         exchangable Ca++ > Mg   , Na+,
         and NHt^"1", and the ion pairs
               and MgSOt,.
         The model has several appli-
         cations other than predict-
         ing the quality of return
         flows.  Those include soil
         reclamation, irrigation
         scheduling, drain spacing
         design, and generating
         inputs to other models.

         The model is designed to
         allow many computer runs to
         be made in a short period of
         time.
                         The model assumes away many
                         real life complications and
                         situations, making it unac-
                         ceptable to some theoreti-
                         cians.  It is already so com-
                         plex as to be unacceptable to
                         many practitioners.
Additional quality parameters
such as phosphates, pesticides
trace elements, etc., are not
included.
                         Additional applications exist
                         which are still beyond the
                         immediate capabilities of the
                         model.
                         Few guidelines are provided
                         the user as to selection of
                         representative input data.
The model is in a "no-mans"  land,
and may be unacceptable to the
two groups for opposing reasons.
A few individuals appear to be
suffering from future shock  and
refuse to examine this and other
simulation models let alone
accept them.

The model is open ended and  addi-
tional parameters can be added.
Other parameters such as ESP,
SAR, hardness, etc., can be  cal-
culated from the existing
parameters.
                                            The model will be  improved  and
                                            expanded in the future.
                                            Research  is badly needed  in this
                                            area.

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Table 5.   (continued) GENERAL MODEL
         Strengths
        Weaknesses
                                                                           Comments
The model simulation begins
at the soil surface and  ter-
minates at the drain  (or
stream}.

Crop uptake of nitrogen  is
simulated.
Chemical reactions are
taken as a function of
waterflow.

The model includes many
bypass configuration
options.

Model verification has been
obtained for several
applications.

The model utilizes chemical
equilibrium approach for
inorganic (salt) reactions.

Nitrogen transformations
are simulated utilizing a
kinetic approach.
Multiple drains/streams cannot
be mixed or combined in this
model.
A fixed crop root distribu-
tion is assumed.  (One can be
entered for each crop.)
Uptake function is crude.

Waterflow is not considered
to be a function of the
chemistries.

The user may be confused as
to which option(s) to use.
                                Additional  field  verification
                                would be  useful.
                                Some inorganic (salt)  species
                                may not be  in  chemical
                                equilibrium.

                                Some rate equations  are  sta-
                                tistical and may not be  valid
                                outside derivation data  set.
                                                               Other models  can  accomplish  this
                                                               function  (e.g.  -  see Volume  III)
                                A function(s) could be  added
                                making the distribution variable.
                                                                An iterative  approach could be
                                                                used to add this  feature.
                                Additional model sensitivity
                                studies could help alleviate this
                                problem.

                                Adequate field verification will
                                require many years.
                                Model verification indicates this
                                assumption is excellent for the
                                species considered.

                                The transition-state nitrifica-
                                tion equation is general.

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          Table 5.   (continued) GENERAL MODEL
                   Strengths                     Weaknesses                          Comments


          Hydrodynamic dispersion is     Dispersion is not modeled       Verification data indicate the
          simulated using a numerical    directly.                       model adequately simulates hydro-
          scheme,                                                         dynamic dispersion.

          Multiple stream tubes are      The flow lines are taken as     Uncertainties about aquifer prop-
          considered in the saturated    time invariant.                 erties make the current approach
          zone.                                                           reasonable.
to
OO

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Table 6.  IRRIGATION SCHEDULING SUBMODEL
         Strengths
        Weaknesses
            Comments
Consumptive crop use is com-
puted using the Jensen-Haise
method.
 The model  makes  use of con-
 cepts  long accepted by soil-
 scientists such  as  field
 capacity,  wilting point,
 and available moisture.
Considerable data are needed
to apply this method.  Solar
radiation data is not col-
lected at all weather
stations.
                               The  effect of soil moisture
                               on plant  growth  is ignored.
Indiscriminate use without
realizing the actual physical
processes involved can lead
to poor results in unusual
situations such as high water
table conditions.
The unsaturated flow model  accepts
consumptive use computed by any
method.  It could easily be
altered to accept basic data  for
other methods such as Blaney-
Criddle.  This is also true of
the scheduling model.

A plant growth model could  be
added, provided sufficient  data
are available to develop and use
it.

These methods have proven their
usefulness.  The unsaturated flow
submodel tends to tie the physical
situation to the older concepts
of soil "constants."

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Table 7.  CHEMICAL EQUILIBRIA SUBMODEL  (Unsaturated Zone)
         Strengths
        Weaknesses
            Comments
Chemical equilibria subpro-
gram simultaneously con-
siders several chemical proc-
esses important in many
Western and other soils,
including solution-
precipitation of lime and
gypsum, cation exchange, ion
pairing of CaSO^ and MgSO^,
and pC02-Ca++-HC03~
interactions.

pCOa is either calculated
as a function of soil mois-
ture content or entered into
the model as part of the
input data.

Activity coefficients are
computed using Debye-
Hiickel equation generalized
for monovalent and divalent
ions.
Chemical equilibria subpro-
gram ignores (1) other solid
phases such as Na2SOtt and
MgC03, (2) the formation of
additional ion pairs, and
(3) pC02-Ca+*-HC03~ interac-
tions in noncalcareous soils.
Ion exchange is limited to
Ca-Na, Ca-Mg, and Na-NH,/
exchange.
Other functional relation-
ships may be more useful
in computing pC02 under
situations such as within
a crop root zone.

Equation could be modified for
each specific ion.  Uncharged
species are assumed to have
activity coefficients equal
to unity.
The model is not applicable where
solid phases other than lime and
gypsum are present at chemical
equilibrium and where additional
ion pairs become significant.
The model tests for supersatura-
tion with respect to lime, but
does not react C02 with the non-
calcareous system.  The model does
not consider ion exchange in acid
soils.

The user must input pC02 values
within the root zone.
These approximations probably are
adequate in light of other
uncertainties.

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Table 8.  NITROGEN TRANSFORMATION SUBMODEL  (Unsaturated Zone)
         Strengths
        Weaknesses
            Comments
Simultaneously considers
nitrification, urea hydrol-
ysis, mineralization, immo-
bilization, NH^* ion
exchange, and denitrifica-
tion  (saturated zone only).
Nitrogen transformation rate
equations include important
variables such as substrate
concentrations, temperature,
soil moisture content, etc.
Nitrification is simulated
using either a statistical
equation, or a transition
state equation.

Transition state equation
includes pH, partial pres-
sure of 02> osmotic effects,
and NHtf* concentrations as
variables.
Ignores nitrogen fixation,
ammonia volatilization,
denitrification (unsaturated
zone).
Most rate equations were
derived statistically based
on experimental data from a
limited number of soils.
Extrapolation to other soils
may be dangerous.

Statistical equation may be
limited to certain soils.

Transition state equation is
general but applies only to
soils with fixed microbial
populations.

Microbial population is
assumed to be fixed in size.
Fixed nitrogen can be added to
soil as input data.
Transition state nitrification
equation is general.
Transition state equation could
be extended to include variable
microbial population size.

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Table 9.  NITROGEN UPTAKE SUBMODEL
         Strengths
        Weaknesses
            Comments
Nitrogen uptake by the crop
is allowed in the form of
NO," and NH, *.
Total nitrogen uptake can
either be inputed to the
model on a semimonthly
basis or computed by
assuming that N uptake is
proportional to consumptive
use.  (The user supplies
the proportionality
constant.)
A fixed ratio between the
uptake of these two species
is used.  Uptake of other
N species is not considered.

Additional nitrogen uptake
functions or schemes are not
considered.
A variable ratio could be added
at a future time.  The major
N species taken as by plants are
N03" and NH,/.

The model is not yet particularly
sophisticated in its handling
of crop N uptake.  This submodel
will be improved in the future.

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         Table  10.  SALT MOVEMENT  SUBMODEL  (Unsaturated  Zone)
                  Strengths
                                       Weaknesses
                                            Comments
CO
GO
Unsaturated waterflow
volumes as computed by the
Unsaturated Flow Program
are used to move soluble
salts into and from each
soil segment (both in
upward and downward
direction).

Soil chemical reactions
are included in the leach-
ing process at each step
in time and space.
                                        Mechanical  dispersion  is  not
                                        simulated directly.
                                         Lateral movement  of  salts
                                         is  not considered.
Some waterflow rates may
be too high to allow chemical
equilibrium as assumed in the
model.
                                The use of several soil segments
                                per profile tends to introduce
                                numerical dispersion.  This tech-
                                nique has yielded good correla-
                                tions with observed data in
                                unsaturated lysimeter tests.

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Table 11.  UNSATURATED FLOW SUBMODEL
         Strengths
        Weaknesses
            Comments
Unsatured waterflow is
simulated in the upward and
downward directions.
The bottom boundary is
taken as the water table.
Consumptive use is computed
using either the Jensen-
Haise or Blaney-Criddle
methods.

Hysteresis in the conduc-
tivity and diffusivity
relations is ignored, sim-
plifying program use and
reducing input requirements.
Two- and three-dimensional
flows are not considered.
Consequently, the model is
not directly applicable to
trickle and furrow irrigation.

The geometric location of the
water table is not changed.
                               Other methods may be more
                               desirable.
                               Hysteresis, especially in the
                               diffusivity, has been consid-
                               ered by many investigators as
                               important in "wetting-drying"
                               systems.
Additional dimensions could be
added but with increased computer
storage requirements and costs.
This tends to overestimate the
upward movement of water by
capillary forces when plant-
induced gradients produce such
flow.  A moving water table loca-
tion could be modeled.

They can be added to the irriga-
tion scheduling or unsaturated
flow models or to both.
                                Inclusion in the model is pos-
                                sible, although it would compli-
                                cate programing, increase computer
                                storage, and lengthen runs.  Ade-
                                quate field data to run the model
                                would be almost impossible to
                                obtain.
Water is extracted from the
root zone according to a
specified root pattern,
using a root extraction
term.
The root distribution is
constant with time.
A variable root pattern could
easily be added.  It could be a
function of time or be based on a
more complicated model of plant
growth (as influenced by tempera-
ture, availability of water, and
the salinity of the soil water).
Field data would be costly.

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Table 12.  DRAINOUT SUBMODEL
         Strengths
        Weaknesses
            Comments
USER drainage equations are
utilized.
Submodel will either pre-
dict the response of a
given drainage system to
deep percolation inputs or
estimate the drain spacing
based on system physical
properties and desired
drainage depth.

Submodel computes the
monthly drain discharges.
Homogeneous, isotropic
conditions are modeled.
This allows use of rela-
tively simple mathematics
that are economical for
computer calculation.
Approximations associated with
USER techniques are included.
User may want discharges over
some alternate time period.
Real situation involves
heterogeneous conditions.
See comments.
USBR drainage equations have seen
a wide application in the United
States and foreign countries.

Model duplicates USBR method for
designing lateral spacings and
consequently is accepted by drain-
age personnel.
Daily discharges are actually
computed by the model and can be
listed or plotted as output.  They
are available in the special plot
file generated by the program.

Weighted permeabilities with depth
are used to account for variabil-
ity of soils.  The storage coeffi-
cient corresponds to a weighted
value in the zone of water table
fluctuations.

-------
         Table 13.  SATURATED FLOW SUBMODEL
                  Strengths
                                       Weaknesses
                                            Comments
U)
Ox
Submodel calculates the
steady-state position (and
corresponding flow tube
volumes) of stream lines
extending from the water
table to the drain, using
potential flow theory.

Submodel calculates the mean
travel times for flow
through each tube.
         Submodel simulates flow
         through a homogeneous, iso-
         tropic aquifer.

         Two-dimensional flow simu-
         lation includes flow to
         subsurface, tile drains.
                                        Stream lines occupy fixed
                                        positions as opposed to the
                                        variable situation in the
                                        field.
The travel times are based on
the computed Darcy velocity
divided by the porosity.  The
porosity is based on volu-
metric considerations and not
on cross-sectional areas.
                               Real aquifers are not homo-
                               geneous and isotropic.
                               Three-dimensional flow and
                               radial flow to wells are not
                               included.
                                This approximation probably is
                                suitable in light of other uncer-
                                tainties in the saturated zone.
                                The Dupuit-Forchheimer assumptions
                                are not invoked.
Research in this area has indi-
cated that use of the porosity
yields good results  (within a few
percent) when compared to actually
measuring areas of flow.  This is
true, even for very  tight, clay
soils.

A submodel capable of simulating
a multilayered aquifer would be
desirable at some future time.

The basic techniques are appli-
cable to any geometric flow system.
Analytical solutions are desirable
as they are cheaper  to use with
the computer.  However, numerical
solutions could be used to simu-
late very complex problems.

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Table 14.  SATURATED CHEMISTRY SUBMODEL
         Strengths
        Weaknesses
            Comments
Simulates inorganic chem-
istry and denitrification
in the saturated zone.
Flow through each stream
tube is considered to be
via complete piston
displacement.

Mechanical dispersion is
simulated by including
multiple-tube elements.

Inorganic chemical reactions
at each point in space.
Submodel has many options
such as salt injection at
the barrier, simulation of
unsaturated chemistry, etc.
Acid soil chemical reactions
not included.

Denitrification submodel is
very crude.

Flow in the field does not
strictly follow this pattern.
Mechanical dispersion is not
not modeled directly.
Contact times near the drain
may be too small to allow
chemical equilibrium to be
achieved.

User may not be completely
aware of all the options.
These deficiencies will be cor-
rected in the future.
Verification data indicate this
approximation is suitable.
Verification data indicate model
approximation is suitable.
Other uncertainties probably
overshadow this approximation.
The Saturated Chemistry user's
manual describes the options.

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         Table 15.  DRAIN EFFLUENT SUBMODEL
                  Strengths
        Weaknesses
Comments
         Combines water from each
         flow tube to form the drain
         water quality mix.
Water quality mix is not
reacted chemically and could
be unstable from a chemical
standpoint.

Submodel requires consider-
able computer memory for runs
involving many years of
simulation.
                                                                        This program could be redone using
                                                                        a different programing  approach
                                                                        to remove this  limitation.
OJ
oo

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                           SECTION VI

                 SUMMARY OF REQUIRED INPUT DATA

From the preceding model description, it is apparent that many physical
and chemical parameters are required for input to the model.  Most of
this information is routinely collected or developed in planning and
designing an irrigation project.  All of the required field data are
listed below:

DRAINAGE DESIGN

The geometry of the drainage system must be specified including:

   a.  Drain spacing.

   b.  Depth to drains.

   c.  Depth to barrier.

   d.  Gravel envelope size or design, used to determine the effective
   radius.

SATURATED MATERIAL PROPERTIES

Saturated material properties should correspond to values used in design-
ing the drainage system and consequently represent average values for
the assumed homogeneous system.  These properties include:

   a.  Saturated hydraulic conductivities (permeabilities).

   b.  Porosity.

   c.  Specific yield or storage coefficient.

UNSATURATED MATERIAL PROPERTIES

In order to simulate unsaturated flow, the following material proper-
ties must be known:

   a.  Hydraulic conductivity (permeability) as a function of moisture
   content.

   b.  Moisture release curves (tension head versus moisture contents).

Direct measurement of the unsaturated hydraulic conductivity by field
or laboratory methods is difficult, time consuming, and expensive.  A
                                   39

-------
limited number of such determinations have been reported in the liter-
ature.  Consequently, in lieu of direct measurements, an approximate
procedure known as Millington-Quirk Method (9) can be used.

This approach recognizes that unsaturated conductivity is related to
pore-size distribution.  The moisture release curve is used in conjunc-
tion with a semiempirical equation.  To assure that the computed and
measured conductivity agree at least at one point, a matching factor
is used.  For practical purposes, it is computed as the ratio of the
measured to the computed conductivity at saturation.  The technique is
simple enough to allow the determination of the spatial variability of
conductivity.(15)  In using the method, moisture contents should be
determined for tensions between 0.05 and 15 atmospheres.  Enough points
should be used to adequately determine the shape of the curve.

SOILS ANALYSIS

Master site soils data should provide the following chemistry data:

   Soil extract data:

   a.  Cations (meq/1 of calcium, magnesium, and sodium).*

   b.  Anions (meq/1 of carbonate, bicarbonate, chloride, and sulfate).

   c.  Extract ratio of water to soil.

   d.  If nitrogen is considered, the meq/1 of ammonium, nitrate, and
   urea.

   Additional data;

   a.  pH.

   b.  Cation exchange capacity in meq/100 g of soil.

   c.  Gypsum content in meq/100 g of soil.

   d.  Indication if soil is calcareous (line present) or not.

   e.  Bulk density in g/cm3 of soil.

   f.  If nitrogen is of interest, the organic nitrogen content in
   micrograms/g of soil and the corresponding carbon-nitrogen ratio;
* In this report meq denotes mi11equivalents, meq/1 denotes milliequiv-
alents/liter and mg/1 or mgm/1 denotes milligrams/liter.  Also cm^ is
cubic centimeters, cm is centimeters, and g is grams.
                                 40

-------
   for use in the transition-state nitrification model, nitrifier-
   population salt response relationship.

Normally, these data are collected in 12-inch intervals or some other
suitable scheme down to the barrier.  The unsaturated chemistry pro-
gram accepts these data horizon by horizon while the saturated chem-
istry program uses a single or average analysis.

CROP INFORMATION

The different types of crops grown in the area to be studied should be
determined and similar crops grouped.  If predictions are to be made
for the entire area, the associated acreage for each group should be
available.  For each group, the following information must be obtained:

   a.  Growing season.

   b.  Root zone depth and root distribution within the zone.

   c.  Evapotranspiration rates (if irrigation scheduling is used,
   solar radiation and temperature; planting, cover and harvest dates;
   cutting dates if alfalfa is included; cutoff date beyond which irri-
   gations are not allowed; thaw and freeze dates for the soil; initial
   soil moisture in root zone on the thaw date; and the percent soil
   moisture in the root zone that may be used before an irrigation is
   required).

   d.  Plant uptake of nitrogen (if nitrogen is considered).

WATER APPLICATIONS

The following data are needed to characterize the water volumes enter-
ing the soil-aquifer system:

   a.  Irrigation schedules and amounts (for model purposes only that
   component entering the soil system is used).

   b.  Days on which precipitation occurs and the corresponding amounts
   (for model purposes only that component entering the soil system is
   used).

   c.  Effective precipitation relationship.

FERTILIZER INFORMATION

Additions of chemicals by fertilizer applications may be included.  If
they are, necessary inputs include:
                                 41

-------
   a.  Fertilization schedules.

   b.  Amounts of constituents in chemical fertilizers (amounts in
   Ib/acre of nitrate, ammonium, urea, calcium, sulfate, and
   carbonate).*

   c.  Depth if plowed in or surface application indicated for each
   application of a chemical fertilizer.

   d.  For each organic nitrogen application the depth of plow down
   (no surface application allowed), carbon-nitrogen ratio, and the
   application rate in Ib/acre.

IRRIGATION WATER ANALYSIS

The chemical analysis of the irrigation water in meq/1 of NHi4+, N03~,
Ca++, Na+, Mg++, HC03~, Cl", C03=, and S
-------
                          SECTION VII

             INTERFACING WITH CONJUNCTIVE USE MODEL

The return flow quality simulation model described in Volume V is
designed to provide, among other outputs, water flow and quality
predictions in a tile drain or stream.  Combination (mixing) of
two or more drains or streams is currently beyond the scope of the
model.  This capability could easily be added in the future.  The
conjunctive use model (Volume III) can supply this additional mixing
or nodal capability provided a suitable model interface is done.

The soil (unsaturated) portion of the conjunctive use model can be
bypassed in favor of the more sophisticated unsaturated flow and
chemistry programs available in the Volume V model.  Also, if the
user wishes to simulate nitrogen transformations, he must utilize
Volume V.

The "tank" type aquifer simulation in the conjunctive use model can
be bypassed in a similar manner in favor of the more detailed satu-
rated flow and chemistry simulations available in the Volume V model.

The user must decide which model or model combinations best fit his
particular application.  Applications exist in which one entire model
should be applied, while others would best be handled by some com-
bination of models.

The details of interfacing these two models are left to the user.
The problem is basically one of converting output files to the current
format and time frame for input to the other model.  Small interfacing
programs such as the Interface for Chemistry Program will be needed.
The user should consult the appropriate user's manuals for details
concerning the proper input/output files.
                                  43

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                          SECTION VIII

                  USER'S MANUAL - OVERALL MODEL

INTRODUCTION

This manual discusses details and procedures common to the model
as a whole.  Data interfacing between subprograms, bypass options,
and general tips on model application and operation are given.

The model is fully operational on the Bureau of Reclamation CDC
CYBER 74-28 computer located in Denver, Colorado.  This computer
is highly time-share oriented with permanent disk storage avail-
able to the user.  On this type system, linkage between subpro-
grams within the model can be done easily and the entire model
operated from a remote terminal.  The model can also be run on
batch computer systems, but more user effort is required.

SUBPROGRAM LINKAGE

After the basic input data have been entered into the computer,
interfacing between subprograms' is accomplished via binary data
files.  These files generally are stored either on magnetic tape
or on permanent disk storage, if available.  Output and input for-
mats have been structured to allow direct interfacing without user
intervention.  The user need only direct the particular submodel
to read the appropriate binary file(s) created by the previous pro-
gram.  Specific discussions of each file are included in the appro-
priate user's manual.  Should the user find it necessary to examine
these binary files, a suitable program can be written to read and
print them.

BYPASS OPTIONS

A user may not have the data or require the detail associated with
some models subprograms.  The following discussion summarizes bypass
options which have shown utility.

Irrigation Scheduling

The irrigation scheduling submodel can be bypassed if the user
inputs pertinent data to the Unsaturated Flow and Drainout Pro-
grams.  This includes crop evapotranspiration data  (p. 79) and  irri-
gation and precipitation dates and amounts in the case of the Unsat-
urated Flow Program  (p. 77).  An option  (CR0P, p. 76) in the Unsatu-
rated Flow Program allows estimation of crop consumptive use by the
Blaney-Criddle method but is limited to a few crops programed into
the model.  The Drainout Program requires data on deep percolation
                                44

-------
amounts from precipitation and  irrigation.  These can be  supplied
from the Irrigation Scheduling  Program or  some other source.

Unsaturated Flow And Unsaturated Chemistry

These two submodels tend to be  large  consumers of computer  execu-
tion time.  However, they are highly  sophisticated programs which
consider many details  (including nitrogen  transformation  and inor-
ganic chemical under nonsteady- and steady-state flow conditions).
The unsaturated chemistry submodel requires input from the  Unsatu-
rated Flow Program or a similar source if  nonsteady flow  is to be
considered.  An option in Unsaturated Chemistry  (ITEST=1, p. 143)
allows input of steady-state flow and moisture content data from
cards.  In this case, additional flow and  soil moisture content
data are not needed.

Bypassing of both the unsaturated flow and unsaturated chemistry
submodels can be done quite easily via card input to the  Saturated
Chemistry Program.  In this case, both quantity and quality of
waters must be specified.  The user either enters values  for the
volume and quality of the deep percolation water or specifies sim-
ilar values for water entering at the soil surface together with
the onfarm irrigation efficiency.  In the  latter case, the  pro-
gram adjusts both quantity and quality in  proportion to the
efficiency.

There is no direct option which allows input of data to the Satu-
rated Chemistry Program from the Unsaturated Flow Program.  If
Unsaturated Flow is utilized, Unsaturated  Chemistry must  be used
to generate input to Saturated Chemistry.  Another program  could
be constructed to take unsaturated flow output from Unsaturated
Flow, assign qualities to these flows, and punch a card deck suit-
able for input to the Saturated Chemistry  Program.

The user should note that a bypass of Unsaturated Chemistry bypasses
the nitrogen transformations in the unsaturated zone.  There is no
alternate means of simulating these reactions within the  model.  It
is possible to use the Saturated Chemistry Program to simulate salt
reactions in the unsaturated zone.  In this case, some characteristic
leaching moisture content(s) is specified  in place of the saturated
value(s).  Each tube in Saturated Chemistry then represents a spe-
cific soil profile and each tube element becomes an unsaturated soil
segment.

Additional options in Unsaturated Chemistry allow the nitrogen trans-
formations and salt reaction portions to be individually  bypassed.
                                 45

-------
Thus, it is possible to consider nitrogen transformations and move-
ment without the salt reactions.  Conversely, salt reactions and
movement can be simulated without the nitrogen transformations.

Saturated Chemistry

This submodel is not needed if the simulation is terminated at the
water table and the program is not being used to simulate chemistry
in the unsaturated zone.  It is possible to use Saturated Chemistry
as purely a routing-type model with no salt chemical reactions con-
sidered.  In this case, SBYPAS (p. 183) is set equal to one.  This
option is extremely useful in cases where only nitrogen species are
being considered in the saturated zone.  If IDN (p. 183) is set equal
to one, a denitrification subroutine is called from Saturated Chemistry.
If the parameter equals zero, the subroutine is bypassed.

Another option in Saturated Chemistry allows injection of salts at
the barrier.  In this case IINJE  (p. 183) is set equal to one, and addi-
tional data (Card Group 4, p. 186) must be inserted into the input deck.
This option allows salts to be added into the system from a source
such as a shale bed.  Pick's Law is utilized.

Still other options in Saturated Chemistry allow user inputed values
for ion exchange coefficients and CC>2 partial pressures.  Appropriate
sections of the user's manual should be consulted for details.

Drain Effluent Prediction

The submodel can be bypassed any time there is no need to mix waters
from the various saturated flow tubes.  This can occur when the
simulation is terminated at the water table, when drain discharges
without any associated qualities are being simulated, or when effects
on the aquifer are desired independently of drain quality.

The Drain Effluent Prediction Program must be utilized if quality
predictions at the drain are desired.

Saturated Flow

The Saturated Flow Program can be bypassed if values for flow tube
volumes and top widths can be determined from alternate sources.
These could be estimates or other simulation models.  The program
is not needed if only monthly drain discharges with no associated
qualities are the objective.  In the latter case, these values are
output from the Drainout Program.
                                  46

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TIPS ON MODEL APPLICATION

Use Of Bypass Options

Selection of the total model or one or more bypass options depends
on many factors.  The user must determine his needs based on data
resources, time and funding allocations, desired accuracy, and
model sensitivity as applied to a particular situation.  No fixed
rules have yet been developed, but common sense applied together
with a critical evaluation of the problem should help provide the
necessary guidance.

The flexibility built into the model was placed there to allow a
wide range of applications.  However, care should be taken not to
abuse this feature.  A program sequence used in one application may
be entirely inappropriate for another.

Several model configurations have shown utility based on experience
over the past few years.   These are illustrated in Figure 2 and in
Figures 6 through 11.  Additional sequences are possible based on
the model bypass options available to the user.  The sequences shown
illustrate some of the more common applications possible with this
model.  Figure 2 contains all of the subprograms contained in the
model.  This sequence allows the maximum amount of detail which the
model can supply.  This configuration is recommended whenever the
data and study requirements indicate that a maximal effort be put
forth.  It is not recommended for screening or reconnaissance-type
applications.

The configuration shown in Figure 6 is a useful computer time-
saving sequence when the unsaturated zone can be ignored.  This
can occur when relatively "clean" surface soils are encountered,
nutrients are not being considered, and "ball park" type answers
are wanted for large acreages.  With this sequence, many computer
runs can be made at a low cost.  No information can be obtained
concerning chemical changes in the unsaturated zone (e.g., the
location of salt precipitation within the unsaturated zone cannot
be determined).

Figure 7 contains a configuration which is similar to that in Fig-
ure 6 except that piston flow at a constant  'leaching1 moisture
content is considered in the unsaturated zone.  The Saturated Chem-
istry Program is used to simulate salt reactions (no nutrient trans-
formations) in the unsaturated region.  It generates output which
can again be inputed to the same program but at the saturated mois-
ture content.  This arrangement uses only slightly more computer
time than that in Figure 6 and includes simulation in the unsat-
urated zone.
                                 47

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    IRRIGATION
   SCHEDULING
                     DEEP
                  PER. VOLUMES

            r
              	I
    DRAINOUT
                            DEEP
                         PER. VOLUMES
SATURATED

   FLOW
                           DRAIN
                          EFFLUENT
                          PREDICTION
                      WATER APP /
                      DEEP PER.VOL.
                       & QUALITY
SATURATED

CHEMISTRY
Assumes  chemistry and flow in  the  unsaturated  zone have
  insignificant  effects on  quality of  drain effluent.  Irrigation
  scheduling  may  be  utilized   or by  passed.
FIGURE  6.  MODEL  BY  PASS  CONFIGURATION   NO. I
                              48

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  IRRIGATION
  SCHEDULING
   DRAINOUT
 WATER APR
     &
QUALITY DATA
                              DEEP
                           PER. VOLUMES
SATURATED

   FLOW
                              DRAIN
                            EFFLUENT
                            PREDICTION
SATURATED

CHEMISTRY
SATURATED

CHEMISTRY
More crudely approxmates  unsaturated flow  by assuming leaching
  fakes  place by piston  displacement at some  constant leaching
  moisture content.
FIGURE  7.   MODEL  BY  PASS  CONFIGURATION  NO. 2
                             49

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       MONTHLY
        DRAIN
       DISCHARGE
                          WATER  APR
                              &
                         QUALITY DATA
                         TUBE VOLUMES
                              &
                          TOP WIDTHS
                         TUBE  TRAVEL
                            TIMES
                    SATURATED

                    CHEMISTRY
                     SATURATED

                     CHEMISTRY
  DRAIN
 EFFLUENT
PREDICTION
All  water  flow parameters must  be  estimated or obtained from
  another  source. Chemistry  routines utilized whenever  possible.
FIGURE  8.  MODEL  BY  PASS  CONFIGURATION  NO.  3
                             50

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          IRRIGATION
         SCHEDULING
        TUBE VOLUMES
          TOP WIDTHS
         TUBE TRAVEL
            TIMES
           MONTHLY
            DRAIN
         DISCHARGES
UNSATURATED
   FLOW
                                        INTERFACE
                                       UNSATURATED
                                       CHEMISTRY
 SATURATED
 CHEMISTRY
   DRAIN
 -EFFLUENT
 PREDICTION
Considers salt and nitrogen chemistry in unsaturated zone. Groundwater
 flow parameters estimated
   FIGURE 9. MODEL BY  PASS CONFIGURATION  NO. 4
                             51

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  IRRIGATION
  SCHEDULING
UNSATURATED
   FLOW
INTERFACE
                                             UNSATURATED
                                              CHEMISTRY
                 Detailed unsaturated zone
FIGURE 10.  MODEL BY  PASS CONFIGURATION  NO. 5

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          IRRIGATION
         SCHEDULING
UNSATURATED
   FLOW
                                   DRAINOUT
 Allows design of drainage system using either output from
  Unsaturated  Flow or deep percolation values from
  Irrigation  Scheduling.
FIGURE II.  MODEL BY  PASS CONFIGURATION  NO. 6
                           53

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Figure 8 illustrates a sequence which is useful when flow through
large aquifers to open drainage channels such as stream and rivers
is being modeled.  In this case, the user inputs estimates for all
the flow parameters and utilizes a simplified chemistry sequence.
Nitrogen transformations in the unsaturated zone cannot be modeled.

The configuration in Figure 9 is somewhat similar to the one in
Figure 8 but allows nutrients as well as salts to be considered
when groundwater flow parameters must be estimated.  In this
case the unsaturated flow subprogram must be included for nonsteady
flows, and the irrigation scheduling subprogram is recommended.

Figure 10 illustrates an abbreviated sequence which allows maximum
detail in the unsaturated zone.  This is useful when the effects
over time of various cultural practices are desired.  Effects of
high irrigation efficiencies, gypsum applications, high salinity
and/or high sodium irrigation waters, etc., can be tested in some
detail in the root zone.

The abbreviated configuration shown in Figure 11 allows design of
drain spacings given porous media properties, depth to barrier,
effective drain radius, depth to drains, and the deep percolation
schedule.  Irrigation scheduling can be used to input monthly deep
percolation volumes into drainout, thus bypassing unsaturated flow.

Intermediate Output

The model is composed of several subprograms which have been inter-
faced.  Thus, intermediate results are generated at various stages
during a simulation run.  The user should take particular care to
examine some of these results (not necessarily the entire binary
interface files) and make certain he is satisfied before proceed-
ing to the next step.  Often an error has been made somewhere in
the input data or assumptions.  If an error is present, early detec-
tion could avoid a costly rerun of some or all of the model.  Check
the results (intermediate and final) against your experience and
judgment and any verification data which may be available.  Never
trust results merely because the computer has generated them.  Gar-
bage (data and assumptions) into a machine always equals garbage
out, and good inputs and assumptions yield qualified predictions.

Printed Output Volume

The output options in the model allow the generation of large vol-
umes of printed output.  Although a certain amount is needed to
verify intermediate results and list the final answers, an attempt
should be made to minimize the volume.  Output can be dumped to
magnetic tape or microfiche in lieu of printing, but again the
question should be asked, "Is all this really necessary?"
                                 54

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Accuracy Versus Computer Run Times

Within the model, several parameters 'are  specified which allow the
user to increase the accuracy of the results at the expense of com-
puter execution times.  In most cases, a  range of values is listed
to give the user an idea of what numbers  to select.  The user must
use his own judgment as to what accuracies are demanded in his par-
ticular application.  Some experimentation may be necessary to more
closely refine some of these criteria.

Conversion To Other Computer Systems

The computer model as listed in Volume V  is operational on a CDC
CYBER 74-28 machine under the FORTRAN Extended Compiler.  Conver-
sion to other CDC 3000, 6000, and 7000 series computers should be
possible with a minimum of problems.  Conversion to machines such
as IBM and Univac is possible, but  a number of difficult conver-
sion problems can be expected.  The user  should use the test run
included in this volume as a check  on the validity of his partic-
ular conversion.

Some consideration should be given  to utilizing this model on the
Bureau of Reclamation computer system.  A remote terminal can be
tied into the system and used to run the  model with a minimum of
effort.  In addition, Bureau personnel can readily assist with any
program difficulties.
                                 55

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                           SECTION IX

                         USER'S MANUAL

                 IRRIGATION SCHEDULING PROGRAM

INTRODUCTION

This program computes irrigation schedules using daily historic pre-
cipitation, temperature and solar radiation data, and associated crop
and soil data.  Crop evapotranspiration is computed using the Jensen-
Haise procedure (7,8).  Irrigation dates and amounts are determined
on the basis of a soil moisture budget accounting procedure.

If desired, a file containing crop evapotranspiration data and pre-
cipitation and irrigation applications can be written in a format
suitable for input to the Unsaturated Flow Program via an interface
utility routine.

Likewise, a file containing deep percolation amounts from rainfall
and irrigation can be written in a format suitable for input to the
Drainout Program via an interface utility routine.

For comparative purposes, weighted-average, monthly irrigation infor-
mation can be computed from the irrigation events for each crop.  These
values can then be compared with a monthly summary of irrigation events
computed using the weighted evapotranspiration values from all crops.
The program reads on file 2 (input) and writes on files 3, 4, 5, and 6
(output).  The FORTRAN program requires about 240,000 octal words on
the Bureau computer.  The storage locations in the computer must be set
to zero before loading this program.

DATA INPUT CARD SEQUENCE AND DATA LIMITATIONS

CARD GROUP 1

  Column      Var    Var                      Variable
    No.      type*  name                    description

Card 1 of 5

 1-5          A    IZIP     Zip code for study area.

    6          X      -      Region number.
  Note:   A is alphanumeric.
         R is real (floating point)
         I is integer (fixed point)
         X is blank or space.
                                 56

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Column Var
No . type
7-36
37-42
45

(The following
46-48
49-50
51-53
54-55
79-80
Card 2 of 5
1- 6
7-72
79-80
Card 3 of 5
1- 6
14-15
A
R
I

10
I
I
I
I
X

X
A
X

X
I
Var
name
ILOCA
ELEV
NELFLG

columns not
LATDEG
LATMIN
LONGDG
LONGMN
-

-
IUSBR
-

-
NOYRS
Name an<
Elevati<
Flag foi
T AT> 
-------
  Column
    No.

   30
31-35
36-40
   52
   54
   56
 Var    Var                      Variable
type   name                    description

  I    NCPTS    Number of combinations of weighted crop
                  percents.
                Min = 0 (if NCPTS = 0, do not include
                  Card 4).
                Max = 5.

  R    PCTWPB   Percent of winter snow that enters the
  R    PCTWPC     soil at the time of soil thaw.  The
                  remaining percent of the snow is con-
                  sidered runoff.
                Note:  Winter precipitation has daily
                  evaporative demand subtracted; the
                  remaining precipitation is summed
                  throughout the winter (carried over
                  from 1  year to the following year)
                  and the accumulated value used at
                  soil thaw.
                PCTWPB is percent for bare ground.
                PCTWPC is percent for ground with cover
                  such as alfalfa or pasture.

  I    IPUNCH   Flag for  writing precip,  irr, and ET on
                  file 4  in  a format suitable for input
                  to the  unsaturated flow program.
                  (Interface utility.)
                If card output is desired, cards may be
                  punched from file 4.
                0 = No write.
                1 = Write.

  I    IFLGCL   Flag for  printing climatic data (file 3).
                0 = No print.
                1 = Print.

  I    IFLGIR   Flag for  printing irrigation schedules
                  by year and by crop.
                0 = No print.
                1 a Print.
                Note:  If both IFLGCL and IFLGIR are zero,
                  only a  summary will be  printed which
                  shows annual values for all years for
                  each crop.
                                  58

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  Column
    No.

   58
 Var    Var
type   name

  I    IWIDTH
   60
       ICARYO
   62
       IWTDP
   64
       IWTIR
   66
       IWTIRD
Card 4 of 5

79-80

 1- 6
  X

  X
                 Variable
               description

Flag for width of printout of irrigation
  schedules.
0 = 132-column printout.
1 »  72-column printout.

Flag for carrying over soil moisture
  and winter precipitation to the follow-
  ing year.
0 = No carry-over.
1 - Carry-over.
Note:  If ICARYO = 1, NDB and NDE should
  be 1 and 366, respectively.

Flag for writing deep perc from rain and
  irrigation in format for input to
  Drainout Model.
0 = No write.
1 = Write.

Flag for computing weighted monthly
  irrigation parameters.
Note:  This weighted average computed by
  irr event was done to compare weighted
  et values from all crops.  An annual
  summary is written on file 6 when this
  flag is set.
0 = Annual summary not printed.
I = Annual summary printed.

Flag for printing detailed event by event
  monthly summary of irrigation weighted
  information on file 6.
0 » Detailed summary not printed.
I = Detailed summary printed.
Card number.

Zip and region.
                                59

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Column
No.
16-45
Var
type
R
Var
name
CPCT
Variable
description
The percentage of each crop acreage to the
total acreage, as it appears chronologi-
cally in card 9, three columns per value,
maximum of 10 values (10 crops) .
Card 4 is repeated for each combination of weighted crop percents.
There should be the same number of these cards as NCPTS.

Card 5 of 5

 1-15          X      --     Zip, region, and other ID.

16-40          I    IPAR     Flag for type of irrigation parameter to
                               be weighted and printed in monthly for-
                               mat.  If IPAR = 0, do not do it.  If
                               IPAR = 1, do it.  Place the flag in the
                               proper column, see following list.
                             Col parameter:
                                16 Evapotranspiration
                                18 Precipitation
                                20 Precip runoff
                                22 Precip entering soil
                                24 Precip deep percolation
                                26 Soil moisture added by precip
                                28 Net et (et reqt to be met by irr)
                                30 Total irrigation application
                                32 Drift loss from sprinkler
                                34 Runoff loss from gravity irr
                                36 Irr appl infiltrating the surface
                                38 Soil moisture added from irrigation
                                40 Deep percolation from irrigation
                             Note:  Parameters listed in col 16-28

Card 5 is included only if IWTIR = 1.

CARD GROUP 2

Card 1 of 5

 1-6          X      -      Zip and region.

 9-10          I    NTHB     Number of the beginning month of poten-
                               tial evapotranspiration calculations.
                                   60

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  Column
    No.

10-14
 Var    Var
type   name

  I    KPCF
15-19


20-21



22-23
  I    IDATA
  I    ICYCLE
24-25
       NCROP
26-29


30-33
       NDETB
       NDETE
                 Variable
               description

Flag for computing et using crop curves
  from cards or polynomials in the CPCOEF
  subroutine.
0 = Read crop curves from cards 12 and 13.
1 = Compute crop curves from polynomials.

Columns used for additional indentifi-
  cation - farm no, field no, etc.

Flag for computing irrigation schedules.
0 = Do not compute schedules.
1 = Compute schedules.

Flag for reading another set of crop data
  (card 9) or reading climatic data (cards
  1-8).
0 = Read card 1 and new year of dim data.
1 = Read card 1, NYR and IREAD only.
Note:   This prevents the inclusion of the
  rest of data in card 1.
2 = Read card 9 for another crop.

Crop identification number:
   1 = Small grain
      : Beans
      •• Peas
      = Potatoes
      = Sugar beets
      = Corn and sorghum
      = Alfalfa
      = Pasture
       Weighted crop does not use a crop
  curve but requires a crop number to
  operate properly.
Note:   For weighted crop use any crop num-
  ber  (must be .GT. 0),

Julian date  (1-366) of planting or
  beginning of growing season.

Julian date  (1-366) of harvest or end
  of growing season.
                                  61

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  Column
    No.

34-37
 Var    Var
type   name

  I    NDCOV
38-41

43-60
  I    NCUTNG

  A    ICROP1
                 Variable
               description

Julian date (1-366) of effective crop
  cover date.
Note:  The Julian dates used should be
  for a leap year  (366).
The program uses a 366-day array but
  leaves out Feb 29 if the year is not
  a leap year.  Dates for southern Idaho
  conditions are listed as follows (after
  Jensen, Wright, and Pratt; estimating
  soil moisture from climate, crop, and
  soil data; Transactions ASAE, Vol 14,
  No. 5, Sept-Oct, 1971, pp. 954-959,
  unpublished Appendix A, May 1971):
   Small grain       At heading
   Beans             Bloom or about
                       50 days after
                       planting.
                     Full bloom or 70 days
                       after planting.
                     About 80 days after
                       planting.
                     About 110 days
                       after planting.
                     About 10 days after
                       tasseling on corn
                       and heading for
                       sorghum.
                     All season except
                       30 days after
                       growth begins in
                       the spring and
                       20 days after
                       cuttings.
   Note:  Cover data for alfalfa are not
     required, as they are taken care of
     internally in the program.
   Pasture           All season except
                       30 days after
                       growth begins in
                       the spring.

Number of cuttings for alfalfa.

Eighteen spaces available for crop name.
                                Peas

                                Potatoes

                                Sugar beets

                                Corn or sorghum



                                Alfalfa
                                   62

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Column Var Var
No . type name
61-66 A IPIANT
67-72 A ICOVER
73-78 A IHARV
79-80 X
Card 2 of 5
1-8 X -
9-12 I NCUT
13-18 A ICIJT
Variable
description
Plant data in month/day nomenclature.
Cover date in month/day nomenclature.
Harvest date in month/day nomenclature.
Card number.

Zip, region, and year.
Julian date (1-366) of first cutting
for alfalfa. Use this card only for
alfalfa.
First cutting date in month/day terms.
Subsequent NCUTS and ICUTS are entered on this card as 14, A6 up
to a maximum of seven cuttings which ends in column 78.
79-80 X
Card 3 of 5
1-20 X
21-75 R RP
Card 4 of 5
1-25 X
26-75 R RD
Card number.

Crop type and other identification.
Crop coefficients from the Jensen-Haise
crop curves at 10 percent intervals,
starting at 0 and ending on 100 percent
cover (a total of 11 values, 5 columns
per coefficient) .

Crop type and other identification.
Crop coefficients at 10-day intervals
                               beginning with the  10th day after full
                               cover and ending with  100th day  (a
                               total of 10 values,  5  columns per
                               coefficient).
Note:  Include cards 3 and 4 only  if KPCF =  0 on card 1.
                                  63

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  Column
    No.

Card 5 of 5

 1-15

16-20



21-25



26-30
 Var    Var
type   name
  X

  I
IBGSEQ
       IENSEQ
       JENDAY
31-35
36-40
  R
AVAIL
       DSMBG
41-45
  R
ADEPCT
46-50
  R
ADEPC1
51-55
       FMEFF
                          Variable
                        description
Zip, region, and other ID if desired.

Julian date (1-366) of soil thaw.  Soil
  moisture budget computations are begun on
  this date.

Julian date (1-366) of soil freeze.  Soil
  moisture budget computations are stopped
  on this date.

Julian date (1-366) of last allowable
  date of irrigation in the season when
  properly specified allows a drying period
  prior to fall harvest.

Inches of available soil  moisture in the
  root zone of the crop specified in
  card 1.

Depleted soil moisture of soil moisture
  budget computations.
If ICARYO = 1 on card 1C  only the DSMBG
  value for the first year will be used.

Allowable depletion percentage.  This is
  the percent of the available soil
  moisture which the crop is allowed to
  use before an irrigation is called for.

Allowable depletion percentage for the
  first irrigation.  Oftentimes this
  percent is less than ADEPCT because
  the root zone is not fully developed
  by the first irrigation.

Irrigation efficiency (in percent) for
  the type of system involved.  Irrigation
  efficiency is defined as soil moisture
  added to the root zone divided by water
  delivered, expressed as a percent.
                                 64

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  Column      Var    Var                      Variable
    No-      .type   name                    description

56-60          R    DRFTLS   Drift loss (in percent)  if a sprinkler
                                system is involved.   This percent would
                                include evaporation  loss and is a per-
                                cent of the water delivered to the field,
                                not the water applied  to the surface.

61-65          R    ROFLS     Runoff loss,  in percent, of the water
                                delivered to the field.

66-68          X

69-70          A    IRRT     Irrigation type.
                              GR -  Gravity
                              Sp -  Sprinkler

Repeat cards 1-5 for each  crop.  Remember,  that on  the  last 1  card
in group 2, ICYCLE is  set  to  0  to  begin reading card  group 3 and
climatic data.

CARD GROUP 3

Card 1 of 32

 1-6          X     -        Zip and region.

 7-8          I    NYR       Last  two digits  of the year.
                              To terminate  the  job set NYR  = 0  by
                                using a blank  card.

13-14          I    IREAD     Flag  for reading  climate data.
                              0,1 = Read only precipitation,  temper-
                                      ature, and solar radiation,  in
                                      that  order.
                              2   = Read precipitation,  evaporation,
                                      temperature, and solar radiation
                                      in that order.
                              3   = Read precipitation,  relative  humid-
                                      ity,  evaporation,  temperature, and
                                      solar  radiation  in that order.
                              4   = Read precipitation,  wind, relative
                                      humidity,  evaporation,  temperature,
                                      and solar radiation in that order.
                              5   = Read only ETP  (potential evapotran-
                                      spiration)  that  has been  computed
                                      previously and placed on  cards.
                                   65

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  Column
    No.
 Var    Var
type   name
15-18

19-22
       NDB

       NDE
23-30
       ATERM
31-38
39-47
48-59
  R
                          Variable
                        description

         A minus sign - in front of any of the
           above IREAD numbers prevents the program
           from using any crop information.
         A minus sign is required for the first
           year of climatic data.  For all the
           following years no minus is used.

         Julian date of beginning climatic data.

         Julian date of ending climatic data.  If
           a full year data are processed, NDE
           should be 366.  The program operates on
           a 366-day array and leaves out Feb 29 if
           the year is not a leap year.

         Average daily maximum temperature for
           the warmest month or the CT coefficient
           in the Jensen-Haise equation,
                    ETP = CT*(T-TX)*RS.
         If the temperature is input, it must be
           preceded with a minus sign as a flag.
           The minus causes CT to be computed in
           subroutine JHCOEF.

         Average daily minimum temperature for the
           warmest month or the TX coefficient in
           the Jensen-Haise equation.  A minus sign
           is not needed with this temperature
           input.  See climatic summary of United
           States for ave daily max and min temps.

         Conversion from gram-calories per square
         •  centimeter (Langleys) to inches of
           evaporation equivalent.  CONVRT is used
           to convert solar radiation in Langleys
           to inches.

            CONVRT = 0.000673 if solar radiation
                       is in Langleys.
            CONVRT = 1.0 if solar radiation is
                       in inches.
SUMETP,  These variables are read in as zeros to
SUMEVP     start sums.
       BTERM
       CONVRT
                                  66

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  Column
    No.

73-78
79-80
 Var    Var
type   name

  Z    OUT
                          Variable
                        description

         This value read in as a blank for
           printing blanks in climatic data
           output.

         Card number.
The following description applies  to  cards  2  through  32 which are
climatic data - set up for  1 year  on  31  cards -  1  card for each day
of the month and 12 columns each representing a  month for that
particular day.
Card 2 of 32

 1- 6

 7- 8

 9-10

11-15
16-20

21-25

26-30

31-35

36-40

41-45
  X

  X

  I

  X
  R

  R

  R

  R

  R

  R
NDAY
DATA

DATA

DATA

DATA

DATA

DATA
Zip code and region.

Last two digits of the year.

Day of the month (1-31).

Identification for data type:
                                 Datatype

                                (Col  11-15)
                                  Prep
                                  Wind
                                  Rel H or
                                   Dewpoint
                                  Evap
                                  Temp
                                  RS  (Solar)
                                  ETP
                                    Card No.

                                   (Col  79-80)
                                        2
                                        3

                                        4
                                        5
                                        6
                                        7
                                        8
Data for January corresponding to NDAY.

Data for February.

Data for March.

Data for April.

Data for May.

Data for June.
                                   67

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  Column      Var    Var                      Variable
    No.      type   name                    description

46-50          R    DATA     Data for July.

51-55          R    DATA     Data for August.

56-60          R    DATA     Data for September.

61-65          R    DATA     Data for October.

66-70          R    DATA     Data for November.

71-75          R    DATA     Data for December.

79-80          R    DATA     Card number.

Detailed information on data input is as follows:

Prep                Precipitation in inches for the day - input as
                      hundredths of an inch.

Wind                Wind in miles per day - no decimals.

Rel H               Relative humidity in percent - no decimals.
  or
  Dewpoint          Dewpoint in degrees F.

Evap.               Pan evaporation in hundredths of an inch
                      (comparative purposes).

Temp                Temperature input as maximum daily temperature in
                      the first three columns of the five-column field,
                      and as minimum daily temperature in the last two
                      columns of the five-column field.  For example:

                                   Field    XXXXX
                                   Temp      9852
                              Maximum daily temp = 98
                              Minimum daily temp = 52

                    Average daily temperature may also be used.  In
                      the case where negative max or min temps are
                      involved, the average temp must be used.
                    (Note:  A negative average may be used.)
                                 68

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  Column      Var    Var                      Variable
    No.      type   name                    description

RS                  Solar radiation  in  Langleys  or  inches  - see CONVRT
                      on card  1.   Langleys  -  no  decimals,  inches -
                      hundredths.

ETP                 Potential  evapotranspiration computed  externally
                      and input  for  scheduling purposes.

The last data card  is a blank  card to exit  the program - See NYR
on card 1.
                                   69

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                            SECTION X

            USER'S MANUAL - UNSATURATED FLOW PROGRAM

INTRODUCTION

This program is designed to simulate one-dimensional unsaturated flow
between the ground surface and the water table.   It includes the
infiltration, redistribution, plant root extraction, and drainage of
soil water under a growing crop.  In particular, this program was
developed as part of a water quality simulation model with the water
contents and movement within the unsaturated zone as well as the deep
percolation to the water table acting as input to other programs.  A
generalized diagram of the system modeled appears in Figure 12.

The program was originally written at the University of Arizona under
a Bureau of Reclamation contract.  The theoretical basis has been
described in Dutt, et al. (5).  However, a number of program improve-
ments and modifications have been made including:

   a.  Improved restart ability, including use of tape, cards and
   printed output.

   b.  Addition of ability to simulate more than 1 year with a single
   run, including commencement of computations with a thaw date and
   stopping them on a freeze date.

   c.  Improved method of handling the upper boundary condition when
   there is no water at the surface and the zero flow condition
   prevails.

   d.  Addition of an option to compute the thaw date application when
   the profile is assumed at field capacity and multiple years are run.

   e.  Improved computation of the consumptive use to assure mass bal-
   ance is maintained.

   f.  Consolidation of all references to a specific soil in program
   M0ISTRE by calling a new subroutine named PR0P.

   g.  Development of a special form of PR0P in which a particular
   functional relationship is used.  This permits soils properties for
   conductivity and diffusivity to be defined by card inputs, eliminat-
   ing the need to modify the source deck.

   h.  Elimination of certain card groups when their options are not
   used.

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        GROWING PLANT OR CROP
                                    SOIL SURFACE

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E
©
             tn
             c
             o
             O
             sz
             2


                                       13
                                  >4
                                   •
                                           UJ
                                           Q
                                                     Q-2


                                                     Q-l
                                              -Top boundary set at
                                                 TBC when water at

                                                 surface except at start
                                                 of run if westart or

                                                 group 4 cards read
hINTERNAL NODES



    Q = number  of nodes

    n  H0RIZON(0)   ,
    u "   DELX       '

    (integer arithmetic)
                                     NODE  NUMBERS
                     -BOTTOM BOUNDARY

                        (stationary, may or may not

                        represent  water table)
                                             -Bottom boundary set at

                                                TBC except at start of run

                                                if  restart data or group

                                                4 read
          FIGURE  12.  MODELED  SYSTEM - UNSATURATED  FLOW
                                         71

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   i.  Modification of input formats to pack more data on a single
   card.

This manual updates and replaces the user's manual found in Dutt,
et al., (5), pp. 31-35.

UNIT NUMBERS

Five input-output devices or files are referenced by the program:
        Unit
    designation

    INPUT
    0UTPUT
    PUNCH
    10
            Unit description
               or purpose

Card input is accomplished by READ statements
without a unit number.  The common input tape
or unit (i.e., the computer system's standard
input device) is understood.

Printed output is generated by PRINT state-
ments without a unit number.  The common out-
put tape or unit (i.e., the computer system's
standard output device) is understood.

Records are written to the punched card
device of the computer by PUNCH statements.

The unit to which computed results are written
on a saved magnetic tape.  An entirely new
tape may be generated or results can be added
to a previously created tape.  This tape is
used as input to the interface program.

The unit to which restart data is written on
a saved magnetic tape.
It is noted that tape 4 (5, p. 32) is no longer used.

DATA DECK STRUCTURE

There are eight basic groups of input cards in the data deck, as shown
in Figure 13, and the variables are defined below.

Groups are numbered to conform with those of the original University
of Arizona user's manual.(1)  The consumptive use routine (C0NUSE)
described in that publication does not correspond to the one in our
program.  An earlier version, in which the Blaney-Criddle constants
and climatic data for two crops (barley and milo) are built into the
program, is used.  Group 5 inputs are not accepted.
                                 72

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                                                             END OF INPUT DECK
           Repeot for eoch year of run
GROUP I
                                                                           GROUP 2
                    /TITLE CARD
                    I    FOR APPLIC.
                                         GROUPS
                                            1 ) Denotes card type within a group
START OF INPUT DECK
      FIGURE 13. DATA  DECK STRUCTURE UNSATURATED  FlDW  SUBMODEL
                                       73

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Group 8 has been added to allow input of soil properties when Campbell's
method is employed to define diffusivity and conductivity relations.
The restart deck does not have a group number, and is described sepa-
rately in a later section.

CARD GROUP 1 - Input-Output Options and Run Conditions
  Column
    No.

Card 1 of 2

 1-5
 6-10
11-15
16-20
 Var    Var                      Variable
type   name                    description
       IPUNCH      Option to allow restart data to be
                     saved at the end of a run.  If

                       IPUNCH = 1, restart data are to
                                  be punched
                       IPUNCH = 2, restart data are to
                                  be written on tape 10
                       IPUNCH = any other value, restart
                                  data are not saved

       IRESTR      Option to allow restart data to be
                     used as input for this run.  If

                       IRESTR = 1, restart data are read
                                  from cards
                       IRESTR = 2, restart data are read
                                  from tape 10
                       IRESTR = any other value, restart
                                  data are not used

       ISAVE       Flag to specify that a previously
                     created output tape 5 is to be used.
                     It is then necessary to position the
                     tape to the correct position for the
                     initial write, using INFIL5 and
                     LLSTRT (below).
                   If ISAVE = 1, use a previously saved
                                   tape 5.

       ITENTH      Option to allow printed results to be
                     outputed at 0.1-day intervals.
                   If ITENTH = 1, print results every
                                    tenth day.
                                  74

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  Column
     No.

 21-25
 26-30



 31-35



 36-40

 41-45
 Var    Var
type   name

  I    INFIL5
       LLSTRT
       MMST0P
       IST0P

       IDEF
46-50
  R    FCAP
 51-55
  I    IP0PT
Card 2 of 2

 1-5            I    AA

 6-10           I    BB
11-15
       CC
              Variable
            description

Initial file number on tape 5 for the
  first write of output data (see
  RESTART OF PROBLEM).

Julian day number of first day for
  which computations are made for the
  initial year of this run.

Julian day number of last day in the
  last year (IST0P) for which compu-
  tations are made.

Stopping or ending year for this run.

Option to select the deficit or
  depleted moisture method of deter-
  mining the thaw date application.
If IDEF = 1, use this option (see
               DEPLETED MOISTURE
               OPTION).

Volumetric moisture content to be
  used as the field capacity value
  when the depleted moisture option
  (IDEF) is used.  FCAP is expressed
  as a decimal (dimensionless).

Option to select the special form of
  subroutine PR0P to compute conduc-
  tivities and diffusivities as a
  function of moisture content.
If IP0PT = 1, then use this form (see
                UNSATURATED FLOW PROP-
                ERTIES) .   A Group 8
                card must then be
                included.
If AA = 1, print the initial input data.

If BB = 1, print computed moisture con-
             tents on a daily basis.

If CC = 1, read initial moisture con-
             tents from Group 4 cards.
                                   75

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  Column      Var    Var
    No.       type   name
16-20
21-25
26-30
I    LL
I    MM
R    BBC
31-35
R    TBC
36-40
41-45
I    YEAR
I    CR0P
              Variable
            description

Julian day number of starting day in a
  full year (i.e., first day for all
  years except initial).

Julian day number of starting day in a
  full year (i.e., last day for all
  years except IST0P).

Volumetric moisture content at the
  bottom boundary expressed as a deci-
  mal (dimensionless).
If BBC = 1, then the bottom boundary
              is set at the TM value.
BBC = 2, then the bottom boundary is
           set at the TS value.
BBC = any other value, the bottom
        boundary is set at this value.

Volumetric moisture content at the top
  boundary expressed as a decimal
  (dimensionless).
If TBC = 1, then the top boundary is
              set at the TM value.
TBC = 2, then the top boundary is set
           at the TS value.
TBC = any other value, the top bound-
        ary is set at this value.

The year number corresponding to the
  initial year of this run.

Crop selector used in computing con-
  sumptive use.
If CR0P = 1, use the Blaney-Criddle
               formula with the con-
               stants in the program
               for barley.
CR0P = 2, use the Blaney-Criddle
            formula with the constants
            in the program for milo.
CR0P = 3, use consumptive use values
            read from cards in Group 7,
                                  76

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  Column
    No.

46-50
56-60


61-65



66-70


71-75
 Var    Var
type   name

  I    M
  R
  R
  R
DELX
       TS
TM
TD
76-80
  R
SM
              Variable
            description

Minimum number of time intervals per
  day for applying the finite differ-
  ence solution.

Distance between nodes for the finite
  difference solution (cm).

Maximum (i.e., usually taken as the
  saturation value) moisture content
  expressed as a decimal  (dimensionless)

Arbitrary moisture content expressed as
  a decimal (dimensionless).

Minimum (i.e., usually taken as perma-
  nent wilting point) moisture content
  expressed as a decimal  (dimension-
  less).  Consumptive use cannot be
  withdrawn by the sink term when this
  value is reached.

Arbitrary initial moisture content for
  internal nodes (i.e., all nodes
  except top and bottom boundary) used
  when the CC and/or restart option
  are not used, expressed as a decimal
  (dimensionless).
CARD GROUP 2 - Water Applications
Card 1 of 2

1-5
6-10
11-13
  I    IC0DE       A numeric code that can be used to
                     identify the crop, climatic condi-
                     tions, irrigation method, etc.  It
                     is merely displayed on output.

  I    IYEAR       Year number identifying the year of
                     inputs.  It is merely displayed on
                     output.

  I    APPS        Number of water applications contained
                     in the type 2 cards of this group
                     for this year (maximum number is 50),
                                   77

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   Column
     No.

 14-77
 Var    Var
type   name

  A    IDENT
 Card 2  of 2

 11-12


 13-14

 15
       M0N
       I DAT
       ADENT
 16-20
       AMI
                          Variable
                        description

            Alphanumeric description to identify
              the water applications.  It is merely
              displayed on output and may include
              information on the crop, climatic
              conditions, and irrigation methods.
            Month of water application where
              January is 1, February is 2, etc.

            Date within month of water application.

            An alphanumeric identifier to denote
              the source of water, for example.
              I = irrigation, R or P = rainfall,
              S = snowmelt, etc.  It is merely
                    displayed on output.

            Amount of application as a volume per
              unit area (inch3/inch2 or inch).
              Water is applied at the start of the
              day.
CARD GROUP 3 - Soil Identification and Depth
Card 1 of 2

 1-2

Card 2 of 2

 3-10


11-20
       IDENT
                   Number of  soil horizons.
            Alphanumeric soil horizon identification
              which is merely displayed on output.
 R
H0RIZ0N     Depth from land surface to lower bound-
              ary of horizon (cm).
CARD GROUP 4 - Initial Moisture Contents
Card 1 of N

 1-10
11-20
etc.
 R    T0(I)
            Initial volumetric soil moisture content
              of each depth node I including top
              and bottom boundary nodes expressed
              as a decimal (dimensionless).   N is
              the number of nodes.
                                  78

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  Column      Var    Var                      Variable
    No-      type   name                    description

CARD GROUP 6 - Root Distribution

Card 1 of 1

 1'10          R    KP(I)        Decimal fraction of roots located in
11-20                              the Ith foot of the soil profile
etc.                               (dimensionless).   KP(1) is  for the
                                   top foot,  KP(2) is for the  second
                                   foot, ...  KP(6) is for the  sixth
                                   foot.

CARD GROUP 7 - Consumptive Use Values

Card 1 of 1

 1-5           I    IC0DE        A numeric code that can be used to
                                   identify the crop, climatic condi-
                                   tions,  irrigation method, etc.   It
                                   is merely displayed on output.

 6-10          I    IYEAR        Year number identifying the year of
                                   inputs.  It  is merely displayed on
                                   output.

11-15          R    U(I)        Semimonthly consumptive use in  the
16-20                              entire  root  zone for period I (acre-
etc.                               inches/acre  or inches).  1=1
                                   denotes January 1 through January  15,
                                   1=2 denotes January 16 through
                                   January 31,  etc.   Thus, the first
                                   period  in a  month is from the. 1st-
                                   15th, while  the second is from the
                                   16th to the  end of the month.

CARD GROUP 8 - Unsaturated Flow Properties

Card 1 of 1

 1_10          R    KSAT        Saturated hydraulic conductivity
                                   (cm/day).

H_20          R    BEMP        Empirical constant b.

21-30          R    AIRENT      Air-entry potential (cm).
                                  79

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NODE SPACING

An idealization of the unsaturated flow system is shown in Figure 12.
The horizon depths given by the group 3 cards, root zone distributions
given by the group 6 card, and the nodal- system are indicated.  The
number of nodes, Q, is based on the depth to the bottom of the deepest
horizon, H0RIZ0N (0), and the DELX value of card 2, group 1.
                       0 - H0RIZ0N(0)   ,
                       V "    DELX

The right hand expression is truncated because Q is integer.  For
example, if H0RIZ0N(0) = 146. cm and DELX = 5.00 cm

                            a 29.2+1 = 30.2 -»• 30                    [2]
                   O » \J \J

If H0RIZ0N(0) = 150. cm and DELX = 5.00 cm it follows that


                                     = 31. -> 31                     [3]


However, the internal representation of real numbers that are con-
sidered exact on input generally results in a stored value that is
slightly different.  Thus, in the previous example, the depth might
be represented internally by a number slightly less than 150.0 cm.
The number of nodes would then be computed as 30 which is a totally
unexpected result.

In general, the use of any real numbers in an integer computation
can produce unexpected results.  Since it is necessary to know Q when
initial conditions are read, it is recommended that the H0RIZ0N(0)
depth be adjusted to assure the desired number of nodes.  In the pre-
vious example, this is accomplished by setting H0RIZ0N(0) = 150. cm.

MOISTURE CONTENTS

The terms soil moisture content and soil moisture movement are used
throughout this manual.  More appropriately, the word "water" should
be substituted for "moisture."  Although a matter of semantics, the
use of "water" is becoming more prevalent in literature.

Variables related to moisture contents include:

   FCAP, card 1, group 1
   BBC, TBC, TS, TD, SM, card 2, group 1
   T0(I), group 4
   similar variables in restart deck.
                                   80

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All contents are on  a  volumetric basis,  defined as:

                     9 -  volume of water in sample
                            total volume  of sample                   »•  ••

Laboratory data are  usually expressed gravimetrically as:
                                 °f water in sample
                                                                     rc;1
                                                                     l J
                         dry weight of soil  in sample

Both the volumetric  and  gravimetric moisture contents  are
dimensionless quantities.   They are related by the  equation:

                             6  = aBD/Dw                              [6]

   where

           BD = bulk  density of the soil      (F/L3)*
           Dw = density of  water              (F/L3)

In the cgs system, the density of water is  approximately
1 gm/cm3.   Expressing the  bulk density in gm/cm3  yields:

                 8  =  ctBD                      (numerically)            [7]

The program uses volumetric moisture contents for input and output.
The above  equations  can  be used to convert  values.  For example, if
the percent moisture by  weight is 30 percent and  the bulk density
is 1.5 gm/cm3, then:

                 9 = (0.30) (1.5) « 0.45                            [gl

Since the  bulk density of  most soils is greater than 1, volumetric
contents will always be  higher than the corresponding  gravimetric
ones.

UNSATURATED FLOW PROPERTIES

The original program made  use  of statement  functions and a series of
IF tests in the  main program (5, p. 31) to  compute  the conductivity
and diffusivity.   Since  the IF tests appear in three places, making
changes in the program for different soils  was not  only a nuisance
* Dimensional Units  are denoted in parentheses where L  denotes  length,
F denotes force, T denotes time,  and - denotes a dimensionless  quantity,
                                    81

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but also an error prone process.  To simplify program use and still
retain sufficient flexibility, the statement functions were removed
and the series of IF tests replaced by a single call to subroutine
PR0P.  The general form of the call is:

                   CALL PR0P  (ZK, TO, K, D)

   where:  1 = volumetric moisture content at which the diffusivity
                 is computed

          ZK = volumetric moisture content at which the conductivity
                 is computed

          TD = volumetric moisture content below which the diffusivity
                 and conductivity are assumed negligible and set to
                 zero

          K  = conductivity at content ZK in cm/day (K is a real
                 variable

          D  = Diffusivity at content Z in cm2/day

The value of TD is obtained from the second card of group 1 and is
normally taken as the wilting point.  Although the conductivity and
diffusivity are treated as constants during a time interval, they are
evaluated at different moisture contents.   For flow between two nodes,
ZK is based on the average contents of the nodes at the start of the
time interval.  Z is based on extrapolation of results from the last
two time levels for each of the nodes, averaged between them (5, equa-
tions [10], [11]).  Under some conditions, it is possible for the
program to compute Z or ZK values greater than the saturation value,
TS on card 2 of group 1.  Since TS is not passed to PR0P in the call
list, provisions should be included to limit the value of Z and ZK to
the saturated value when this occurs.

Subroutine PR0P can contain any degree of detail to approximate field
data.  Methods may vary from using tabular values to employing exponen-
tial forms (5, p. 31).  A sample is given in the section entitled
"Example of Subroutine PR0P."

The current form of M0ISTRE does not pass information to subroutine
PR0P specifying the depth or node number at which the properties are
computed.  This is due to the fact that only homogeneous soils are
allowed.   Original intentions were to allow for layered soils, hence
the structure of the group 3 cards.  (As noted in 5, footnote A,
Table 23, p.33):

      "Soil 'horizons' referred to in this context do not cor-
      respond to morphological soil horizons.  Program M0ISTRE
                                   82

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      models moisture movement  in uniform soils only, so soil
      'horizons' as referred to here have no function except to
      correspond to the  'chemistry horizons' in the Biological-
      Chemical Program for convenience."

The horizon references have been left in the program for future expan-
sion to handle variable  flow properties.  This would require the addi-
tion of the node number  in the  call list of PR0P.  Properties could
then be related to a particular horizon.

A special form of PR0P has been developed for use with a specific
form of the moisture-release curve, as  outlined by Campbell (23).
This method is purported to be  as good  as the Millington-Quirk
method  (9) which is presently finding wide use and acceptance.
This routine receives some data through a C0MM0N block.  The method
is detailed and is outlined as  follows:

   a.   Plot moisture-release data on  log-log paper.

   b.   If a straight line fits  the plotted data reasonably well, then
   the moisture-release  curve is approximated by an exponential form
   and  the method of Campbell can be  used.

   c.   Evaluate the slope of the line to obtain BEMP and the air-entry
   potential AIRENT.

   d.   Select the option by setting  IP0PT=1 on the first card of
   group 1.

   e.   Include the group 8 card on  input.

INITIAL BOUNDARY CONDITIONS

The top and bottom boundary conditions  are  established by variables
on card 2 of group 1.  Values are  set as  follows:

   a.   Top boundary  (TBC) -

      if TBC =  1,                set  TBC = TM
      if TBC *  2,                set  TBC = TS
      if TBC = any other value, use  TBC as  read

   b.   Bottom boundary  (BBC)  -

      if BBC -  1,                set  BBC = TM
      if BBC »  2,                set  BBC = TS
      if BBC = any other value, use BBC as  read
                                  83

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When initial conditions are not read from the group 4 cards or restart
data from cards or tape, all nodes other than the boundary nodes  (i.e.,
internal nodes) are initialized to SM.  Should either the group 4 cards
(CC=1) or restart data  (IRESTR=1 or 2) be read, values must be included
for both boundaries.  These override the TBC and BBC values at the
start of the first time step.  When computations are finished for this
step, the top boundary condition depends on the availability of water
at the surface for infiltration while the bottom boundary condition
reverts to the BBC value (see MASS BALANCE).  If water does remain at
the surface, the top boundary is set at TBC.

Logically, the group 4 input option (CC=1) and restart options (IRESTR=1
or 2) are not used for the same run.  However, if they are, the initial
moisture contents read from the restart data override those from the
group 4 cards.

CONSUMPTIVE USE VALUES

Values read from the group 7 cards (CR0P=3) are the total consumptive
use values for each semimonthly period.  The first period for a given
month extends from the 1st through the 15th while the second extends
from the 16th to the last day of the particular month.  Consumptive
use is withdrawn at a uniform rate equal to the total divided by the
number of days in the given semimonthly period.

If the starting date of the run is not the 1st or the 16th, it is
necessary to adjust the input values to obtain the correct withdrawal.
Thus, if:

   U = total required consumptive use for period (acre-inches/acre)
   N = number of days in full period
   A = actual number of days in period based on starting date
   U = adjusted or input consumptive use (acre-inches/acre)


                           u = ^                                   m

For example, if the total consumptive use to be removed is 1.00 inch
and the starting date is July 13, then:

                    U = (LOO inch) (15) = 5>QO inches             [1Q]


It is seen that the above equation merely converts the total consump-
tive use to the required withdrawal rate (U/D) and then computes the
input value by using the total number of days in the period.  The
same approach is employed when the ending date of the run does not
fall on the 15th or the last day in the month.
                                  84

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DEPLETED MOISTURE OPTION

A special option is available to handle winter precipitation  for areas
experiencing an annual  freeze-thaw cycle.   It is  selected by  setting
IDEF=1 on the first card  of group 1.   The  method  is  based on  the
assumption that the entire profile is at least at a  moisture  content,
FCAP, normally considered to be the field  capacity.

The starting day for  a  full year is considered as the  thaw date while
the terminating day is  the freeze date.   No further  infiltration or
redistribution of moisture occurs after the freeze date until the
thaw date of the next year.  Winter precipitation during the  period
is assumed sufficient to  raise the moisture level throughout  the pro-
file to the FCAP value.   Any excess is presumed to melt and run off
or to evaporate.

The required quantity of  water to raise the moisture content  at each
node to FCAP is accumulated on the freeze  date.   If  a  node is already
higher, there is no reduction in the total.  This total is printed on
output and used as the  first application for the  next  year.

Water application data  for the succeeding  year must  include the
depleted moisture as  the  first application.  The  total number of appli-
cations  (APPS) must include it and the date and month  specified for it.
The amount should be  left blank.  Although the application date
normally coincides with the thaw date, this is not necessary.

The depleted moisture option does not function until the end of the
first year's computations.  Consequently,  if the  same  technique is
employed for the starting year, the application must be computed and
included on the group 2 card.  Similarly,  restart data do not include
the quantity of depleted  moisture from the previous  year.

The following message is  printed at the end of each  year's computa-
tions when the depleted moisture option is used:

   MOISTURE DEPLETED  FOR  YEAR = yy, MONTH  = mm, DATE = dd  (DAY NUMBER
     = jj) IS = ii  INCHES

   where:  yy = year  number of run
           mm = month number with mm=l for January,  mm=2 for  February,
                  etc.
           dd = date  within month
           jj = Julian  day number
           ii = depleted  moisture in the entire column in  inches at
                  the end of the given date

yy, mm, and dd as well  as jj correspond to the last  day  in a  full year
or the stopping day of  the run for the last year  run.
                                   85

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STARTING AND STOPPING DATES

Changes have been made to the program to allow runs beyond 1 year,
thus removing the limitations noted in Dutt, et al.  (5, p. 35).   All
dates are Julian with a perpetual calendar assumed  (no leap years).

The starting year number of the run is given as YEAR  (card type 2,
group 1) while the ending year is IST0P (card 1, group 1).  These
years may be integer numbers starting with 1, 2, etc., or actual years
such as 1975, 1980, etc.  Checks are made at the finish of each year's
computations to determine if the run is complete.  Consequently, at
least a single year is run, even if IST0P is less than YEAR.  In gen-
eral, the number of years in the run is (YEAR-IST0P+1).

The first year's computations commence with the Julian date LLSTRT
(card 1, group 1) and end with MM (card 2, group 1) unless YEAR =
IST0P.  In this case the last day of computations is MMST0P (card
type 1, group 1).  Subsequent years commence with date LL (card 2,
group 1) and end with day MM unless the last year (IST0P) is being
processed in which case the ending date is MMST0P.

As an example, if computations are desired to commence on July 12,
1975, and to end on November 14, 1977, with a thaw date of May 12 and
freeze date of November 27, the following values are used:

   YEAR   = 1975                     IST0P  = 1977
   LLSTRT = 193 (i.e., July 12)      MMST0P = 318 (i.e., Nov.  14)
   LL     = 132 (i.e., May 12)       MM     = 331 (i.e., Nov.  27)

The starting and ending dates for each year of the run are:

      Year                Starting date          Ending date

      1975                     193                   331
      1976                     132                   331
      1977                     132                   318

If there is no freeze-thaw cycle, then LL=1 (Jan. 1) and MM=365
(Dec. 31).  Other variables are used in the manner outlined above.

DEFICIT MOISTURE

During a given time step, the program compares the quantity of water
specified for removal by the plants at a given node to the available
moisture.   The available moisture is taken as the difference between
the moisture content at the start of the period and the input mini-
mum level, TD, usually taken as the permanent wilting point.  Should
                                  86

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the consumptive use exceed the available water, the difference is
computed and saved as the deficit moisture, and the consumptive use
actually removed is reduced to the available water.  This technique
ignores the possibility of water moving from adjacent nodes during
the time step.  Since contents are very low resulting in low trans-
mission rates, this appears to be a  logical approach.

Should moisture levels rise above the minimum at later times, the
program again attempts to remove the specified consumptive use.

The method outlined above is obviously a simple approach to a complex
problem.  The availability of water  to a plant depends on soil mois-
ture levels, salinity conditions in  the soil profile, crop type,
present health of the plants, stage  of plant development, as well as
the physical soil properties.  In addition, the relationship of the
entire root system to required water needs of the plant is involved.

When printed output is obtained at tenth-day intervals, a deficit
moisture condition results in the message:

   DEFICIT MOISTURE SITUATION ENCOUNTERED nn TIMES THIS TENTH DAY.
   AMOUNT IS aa CM

   Where:  nn is the number of individual situations that a
             moisture deficit was encountered
           aa is the accumulative deficit in cm3/cm2 or cm

A similar message appears with the daily output, except values corre-
spond to totals for the day and the  message reads  .  . . TIMES THIS
DAY  ... instead of  ... TIMES THIS TENTH DAY  ....

The cumulative deficit since the start of the run  is DEFAMC which is
routinely printed on output, even if it is zero.   It is also included
in the restart deck as is the cumulative deficit at a given node,
Z(J), since the start of the run.

MASS BALANCE

A mass balance check is included to  assure program integrity and to
provide a means of assessing the adequacy of the time steps being
used in the simulation.  The entire  soil column  is considered and an
accounting made of all inputs and outputs of water.  Results of the
check appear with the printed output.  The individual components are
carried forward in the restart data.
                                    87

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The usual conservation of mass equation:

           mass in - mass out = change in mass storage             [11]

is applied to the soil column.  The only water entering the column
is from infiltration of precipitation and irrigation water.  Water
leaves the system as consumptive use and as deep percolation (leachate)
across the water table.

Defining:

   ETS = cumulative infiltration (water percolating through the sur-
           face into the column).

   ET  = cumulative plant evapotranspiration actually removed.

   CL  = cumulative water leached through the bottom of the column
           (deep percolation).  A positive value denotes water
           leaving the column and a negative value denotes water
           moving into the column from below the water table.

   DIP = change in storage of water in the soil column since start
           of run (final quantity less the initial quantity).

The units of the variables on output are in cm3 of water per cm2 of
surface area or simply cm.

The mass balance equation becomes:

                 ETS - CL - ET = DIP                               [12]

from which:      CL = ETS - ET - DIP                               [13]

Letting:         CHECK = ETS - ET - DIP                            [14]

                 CL = CHECK                                        [15]

Printed output includes CL, CHECK,  ETS, ET, and DIP.  The CL and CHECK
values should compare reasonably well.  Values for DIP and, consequently,
CHECK are only updated at the end of each day.  Therefore when 0.1-day
output is selected, the mass balance check is only correct at the end
of each day.

The ET value is the quantity of water actually removed by the program.
An adjustment procedure is included to assure that this value equals
that on input when there are no deficits.  This procedure is based on
the node spacing, root distribution with depth, and the program method

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for computing the withdrawal  at each node.   When low-moisture  levels
occur and a deficit moisture  (DEFAMC)  results,  the  total  consumptive
use on input should equal  DEFAMC + ET.   The mass balance  equation is
unaffected.

A factor related to the mass  balance computations is  the  approximate
manner of treating the upper  boundary.   When water  remains at  the
surface, the moisture content of the upper  boundary is TBC.  Once
all the water infiltrates,  an extrapolation procedure is  used  to
estimate the top boundary  moisture content  for  the  next time step.
There is no assurance that the zero flow condition  (i.e., a specified
gradient) is satisfied.  Consequently,  it is found  that the program
computes water  crossing the surface (in both directions)  at later
times.

The ETS value is the total quantity of water crossing the surface and
is computed on  the basis of gradients and soil  properties as are all
flows.  The quantity of water at the surface is stored in an accumu-
lator called HED which also appears in the  restart  data.  When HED is
less than or equal to zero, all the water has infiltrated.  However,
if additional water is computed as entering the column, it reduces
HED further  (i.e., HED becomes more negative) and is  included  in both
ETS and a value called CI.  Consequently, CI includes the net  infil-
tration when water is at the  surface plus any infiltration resulting
from errors in  handling the upper boundary.

When there is no water at  the surface and a quantity  of water  is com-
puted as leaving the column,  flowing upward across  the surface, it is
stored in a separate accumulator called CNA.  It does not alter the
value of HED or CI, but will  reduce ETS. The cumulative  value of CNA
for the run is  CNI.

From the above  description:

                         ETS  = CI - CNI                           [16]

It is emphasized that the  CNA value represents  the  quantity of water
moving upward since all of the surface water from the last applica-
tion infiltrated the column.   It is a result of the approximate treat-
ment of the upper boundary and as such is an error.   The  corresponding
error due to downward movement is the HED which increases negatively
until the next  water application.  When the application date is
reached, the program applies:

                       HED +  CNA + AMT(I)                         I17!

HED and CNA tend to compensate.  Together they represent  the error
produced in handling the upper boundary which alters  the  application

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specified on input.  After the last application is made for a given
year, the program checks the value of CNA.  If it is appreciable,
(CNA greater than 0.05 cm), an application of HED + CNA is applied
the next day.  This assures the value of ETS compares closely with
the accumulated AMT(I) specified on input.  It is noted that units
on CNA, CNI, CI, and HED are all in cur of water per cm2 of area or
simply cm on the printed output.

RESTART OF PROBLEM

A problem may be run in successive stages using the restart capabil-
ity.  Data necessary to restart a problem are automatically printed
during the run and may also be punched on cards or written to magnetic
tape (or disc storage) at the end of the run.   The data can be used
in a subsequent run to continue the problem solution.

Restart data are directed to a permanent storage medium using the
IPUNCH option (card 1, group 1).  If:

   IPUNCH = 1  data are punched on cards
   IPUNCH = 2  data are written to unit 10 which may be equipped to
                 a magnetic tape or to permanent disc storage
   IPUNCH = any other value, no restart data are placed on a
              permanent storage medium

Organizational structure on unit 10 and deck structure for the punch
file are shown in Figure 14.  Tape 10 is unformatted (binary) while
the punch cards are formatted as indicated in Figure 14.  The vari-
ables are defined below.

   YEAR, M0NTH, IDTE   The year, month, and date corresponding to
                       the time for which the restart data were
                       written.  Month = 1 for January, 2 for
                       February, etc.

   II                  The Julian day number corresponding to M0NTH
                       and IDTE.

   IR                  Maximum rate of soil water movement between
                       nodes.  It is used internally by the program
                       to select the time increment for solving the
                       finite difference equations (cm/day).

   L                   Number of next irrigation or precipitation
                       event.
                                   90

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      B0T( beginning of tape)                                       E0F(end of file mark)

     | LOGICAL RECORD I |  [LOGICAL RECORD 2 | | LOGICAL RECORD 3 | | LOGICAL RECORD 41  | LOGICAL RECORD 51
                  J L
                                 J L
                      (TN(J),J = I,Q)    (FN(J),J=I,Q)   (ANT(J),J = I,Q)     ( Z (J), J=I,Q)
               YEAR, M0NTH,1DTE,II,CL,CHECK, IR,L,HED,C0NST,CI ,ETS,ET,CNA,CNI,DEFAMC
                             TAPE  10 RESTART  DATA
                                                 (Z(J),J=I,Q)
          6 VALUES PER  CARD

   4(Q-l)/6+ I  Cords for each type of dateT/
/_
                                         (ANT(J),J = I,C
                                 /
/(FN(J),J=I,Q)

rN(J),J = l,Q)



/
                    DEFAMC
              C0NST,C!,ETS, ET, CN A.CNI
     /YEAR,M0NTH,IDTE ,CL,
          CHECK,I R,L,HEAD
                                                       FORMAT (6EI3.6)
                                      FORMAT (15,213,14, 3E,13.6,13,EI3.6)
FIGURE  14. PUNCHED CARD  RESTART DECK-UNSATURATED  FLOW  SUBMODEL
                                   ( RESTART  DATA)
                                          91

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   C0NST



   Q


   TN(J)


   FN(J)



   ANT(J)
   Z(J)
Initial quantity of water in the unsaturated
soil column (cm3 of water per cm2 of surface
area or cm).

Number of nodes in the unsaturated column used
to solve the finite difference equations.

Present moisture content at node J
(dimensionless).

Present rate of water movement between nodes
J and J + 1 (i.e., between node J and the next
one below it) (cm/day).

Anticipated moisture content for the next time
step to be used in evaluating the diffusivity
at node J (dimensionless) (see UNSATURATED
FLOW PROPERTIES).

Cumulative deficit moisture at node J (cm3
of water per cm2 of surface area or cm).
   CL, CHECK, HED, CI, ETS, ET, CNA, CNI - See MASS BALANCE.

   DEFAMC              See DEFICIT MOISTURE

Restart data are automatically written to the common output device
(printed output) regardless of the value of IPUNCH.  Data are written
at the end of 15th day, at the end of each month, and at the end of
the run, regardless of the termination date.  This output may be used
to generate the required restart deck if an abnormal termination
occurs.  Items corresponding to those in logical records 2-5 are
listed in nodal order, starting at the surface with seven values per
line.

Restart data generated by the IPUNCH option are used by the program
by setting the restart flag IRESTR appropriately.  If:

   IRESTR = 1  data are read from cards (Figures 13 and 14)
   IRESTR = 2  data are read from unit 10
   IRESTR = any other value, restart data are not used.

Restart data are intended to be used for the day following the date
on which it was written.  The program does not check dates although
they do appear with the printed input data.

When a problem is restarted and tape 5 output is saved, it is necessary
to position tape 5 correctly (see OUTPUT).
                                92

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When restart data are read,  the CC=1 option  should not be used.  How-
ever, if it is, moisture  contents  from  the group 4 cards will be over-
ridden by the restart data  (see INITIAL AND  BOUNDARY CONDITIONS).  Run
information and options  (group 1),  water  applications  (group 2), hori-
zon data (group 3) as well  as root  zone data (group 6), consumptive
use values  (group 7), and unsaturated flow properties  (group 8) when
used must be included.  Starting and ending  dates as well as water
applications for the entire year must be  included, corresponding to
the year in which the restart data  were developed.

LIMITATIONS

The program has been developed with the following restrictions:

   a.  Only homogeneous soils are allowed.   The extension to layered
   conditions would be relatively  simple  (see UNSATURATED FLOW
   PROPERTIES).

   b.  The bottom boundary  is at a  fixed  location.  The fluctuating
   water table is not treated.

   c.  A single, constant root pattern  is used.

Problem size is restricted  by allocated storage to:

   a.  maximum number of  nodes = 60

   b.  maximum number of  water applications  = 50

   c.  maximum number of  horizons  = 9

There is no limit on the  number of  years  run.

Use of the CR0P = 1 or 2  option is  not  recommended since the Blaney-
Criddle coefficients are  for two crops  based on Arizona data (see
DATA DECK STRUCTURE).

OUTPUT

Program output consists of  printed  listings, punched cards, and both
computed results and restart data written to magnetic tape  (or disc
storage).

   a.  Printed data are listed by the program on the file called
   0UTPUT.  It includes both standard and optional output.
                                  93

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   (1)  Standard output includes:

      (a)  Input data:  unsaturated flow properties when Campbell's
      method is used, water application dates and amounts, evapo-
      transpiration values, and restart data read from tape or
      cards when the run is restarted.

      (b)  Computed results:  the amount of water applied on a given
      date; mass balance results, upper boundary information, def-
      icit moisture values and the number of time increments used
      for a given day for each day of the run; and restart data at
      the end of the 15th, the month, and the run.

   (2) Optional printed output includes:

      (a)  Input data:  control and run parameters, initial mois-
      ture contents, soil horizon data, and root distributions if
      AA = 1 on card 2, group 1.

      (b)  Computed results:  moisture contents on a daily basis if
      BB = 1 on card 2, group 1; mass balance results, upper bound-
      ary information, deficit moisture values, the number of time
      increments used thus far for the day, and moisture contents at
      0.1-day intervals if ITENTH = 1 on card 1, group 1.

   (3)  Special printed messages include:

      (a)  Depleted moisture message at the end of each year and at
      the end of the run when IDEF = 1 on card 1, group 1 (see
      DEPLETED MOISTURE OPTION).

      (b)  Deficit moisture message whenever a deficit is encoun-
      tered during a given day (see DEFICIT MOISTURE).

      (c)  Unstable solution message whenever this situation is
      encountered (see HINTS ON USE).

      (d)  Error messages regarding tape 5 when a saved tape is
      used (ISAVE = 1 on the group 1 card) and the error condition
      is detected (see discussion below on tape 5 output).

   The deficit moisture and unstable solution messages are given
   at the end of each 0.1 day when ITENTH = 1 and the given situ-
   ation occurs.

b.  Restart data are included in the printed output and may be
written to unit 10 or to the punch file (see RESTART OF PROBLEM).
                                 94

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   c.  Computed results are written by  the program on unit  5 as stand-
   ard output at the end of each  0.1  day.  Data are written without
   format in binary form by the single  write  statement:

      WRITE (5)  YEAR, II, XT, CI, CL,  HED, ETS, DEPAMC,  (J, TN(J),
                   Z(J), SF(J), U(J), J=l, Q)

      Where:  YEAR  = current year number
              II    = Julian day  number
              XT    = time within the day corresponding to  the
                        written data  (i.e., 0.1 day, 0.2 day, . .  .
                        1.0 day)
              CI, CL, HED, ETS -  See  MASS BALANCE
              J     = node number (see  NODE SPACING)
              TN(J) = volumetric  moisture content at time XT for
                        node J  (cm3/cm3 or -)
              Z(J)  = deficit moisture  at node J during the last
                        0.1-day interval (cm3 of water/cm2  of sur-
                        face area or  cm)
              SF(J) = total soil  moisture flux  (i.e., total quantity
                        of water  moving) between node J and (J+l)
                        during the last 0.1 day (cm3 of water/cm2 of
                        surface area  or cm)
              U(J)  = evapotranspiration rate for node J based on the
                        input data  (cm3 of water/cm2 of surface
                        area/day  or cm/day)

An end-of-file mark is written at the end of  each year's data.  Con-
sequently, each year's data can be considered a single logical file.
When a problem is restarted and a saved tape  5 is to be written to,
it is necessary to position it for the  initial write.

Use of a saved tape is indicated  by setting ISAVE=1 on the  group 1
card.  The initial file to which  additional computed results are to
be added is denoted as INFIL5 on  the  group 1  card.  The program skips
over the first (INFIL5-1) files,  positioning  tape 5 to the  first
record in INFIL5.  If the starting date LLSTRT equals LL  (the first
day in a full year), the tape is  assumed positioned and ready to go
(i.e., INFIL5 is empty).  If LLSTRT is  not equal to LL, 10  records
per day are read, the date read is checked against (LLSTRT-1), with
the process stopping when it is found.   The next write will then
generate data for the first 0.1-day interval  in day LLSTRT.

Two abnormal situations can occur during the  process, resulting in
error messages and program termination:

   a.  The end-of-file is reached before day  number  (LLSTRT-1) is
   reached.  Restarting at LLSTRT would leave a gap in the  records
                                  95

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   in INFIL5.  This situation includes the case of an empty file.
   The following message is printed:

      END FILE FOUND ON TAPE 5 BEFORE DAY NO. LLSTRT-1 FOUND,
      EXECUTION TERMINATED

   b.  The first day number read from the file may exceed LLSTRT.
   It is then impossible to position tape 5 correctly.  The follow-
   ing message is printed:

      DAY READ FROM TAPE 5 EQUALS OR IS GREATER THAN STARTING
      DAY, EXECUTION TERMINATED

Tape 5 is intended to be used as input to an interface program which
interfaces the unsaturated flow program with an unsaturated chemistry
and a drainout program.

HINTS ON USE

The following items are intended to guide the user in the intelli-
gent use of the program.  Some of the items are discussed elsewhere
in the user's manual but are noted here for ready reference.

Selection of Maximum Time Step

Mass balance errors generally increase as the average time step for
solving the finite difference equations increases.  This is due to
errors inherent in using finite differences as well as those result-
ing from the techniques that are used to handle the nonlinear soil
properties.

Minimum computer costs dictate as large a time step as practical.
The time step is automatically reduced when water is applied.  This
reduction is required because moisture conditions and, consequently,
the unsaturated flow properties are rapidly changing with time.  The
reduced step is 0.001 day corresponding to 1,000 steps per day.  These
steps are gradually increased as the maximum rate of moisture movement
in the profile decreases.  The user limits the maximum size to M steps
per day on card 2, group 1.

Since results are written to tape 5 on a 0.1-day basis, the largest
time step is logically 0.1 day (M=10).  However, the program checks
the size of the step it is about to use and reduces it, if necessary,
to obtain computed results at the 0.1-day interval.

Because of this, situations can occur in which successive time steps
exhibit large variations in size.  For example, steps of 0.045, 0.050,
and 0.005 might result from specifying M=20.  Experience has shown that
                                 96

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better results are obtained when  the  tenth-day period is divided into
more nearly equal steps,  e.g.,  0.035,  0.035,  and  0.030.  This is due
to the method of handling the upper boundary  and  of estimating the
anticipated moisture content used in  evaluating the diffusivity f5
equations  [10],  [11], p.  7).

For most soils, a value of M=30 is recommended.   The actual number
of time steps used is given as  NSTEPS  in the  printed output.  Both
mass balance results and  conditions at the upper  boundary should be
used in selecting the appropriate value of M.

Unstable Solution

Because of the methods used to  deal with the  nonlinear flow proper-
ties, the approximate treatment of the upper  boundary, and numerical
solution errors, the computed moisture contents may exceed the physi-
cal bounds.  When the computed  value  is less  than zero or greater than
saturation (i.e., TS) at  a node for one time  step, a counter is incre-
mented.  The total number of such occurrences is  noted in the printed
output for each 0.1 day when ITENTH=1  and for each day.  The printed
message is:

   UNSTABLE SOLUTION SITUATION  ENCOUNTERED nn TIMES THIS TENTH
   DAY or  (. .  . THIS DAY)

Normally, this situation  only occurs on application dates when the
soil profile is very dry  and the  amount of applied water large.   Mois-
ture contents then exceed TS.   Under rare conditions, moisture levels
may fall below zero, especially when the wilting  point, TD, is very
near zero.  In either case, if  the count is low and computed contents
exceed the limits only slightly (say 0.01 or  less), the situation is
not serious and can be ignored.   Generally, major difficulties result
only when very heavy soils (low conductivity) are encountered.  In
this case, improvement can be made by  increasing  the number of nodes
used to simulate the soil column.

Adequacy of Unsaturated Flow Properties

The unsaturated flow properties should be evaluated by performing sev-
eral simulations to duplicate soil properties commonly used by soil
scientists.  These include field  capacity, specific yield, wilting
point, and water holding  capacity.

Uniform Initial Conditions

Whenever uniform initial  conditions are desired,  the value of CC on
the type 2, group 1 card  should be left blank or  set to zero.  The
                                  97

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SM value on the same card is then used for initial conditions at all
internal nodes.

Deficit Moisture

Whenever the deficit moisture situation is encountered, the reason for
it should be determined.  Normal irrigation practices attempt to pre-
vent such conditions.  Items that should be considered include the
unsaturated flow properties, consumptive use rates, and the irrigation
schedules.

Boundary Conditions

The top and bottom boundary conditions need not be set at saturation.
The top boundary condition, used when water is at the surface, can be
reduced to account for surface resistance due to compaction, inwashing,
swelling of colloids, and the breakdown of soil structure.  The bottom
boundary may not represent a water table.  Consequently, any moisture
condition can be used to model it, corresponding to the desired tension.

EXAMPLE OF SUBROUTINE PR0P

Introduction

When the method of Campbell is not used to compute the unsaturated flow
properties, the user must supply his own property subroutine PR0P.   The
general form of the call is:

                   CALL PR0P (Z, ZK, TO, K, D)

   where:  Z  = volumetric moisture content at which the diffusivity
                  is computed
           ZK = volumetric moisture content at which the conductivity
                  is computed
           TO = volumetric moisture content below which the diffusivity
                  and conductivity are assumed negligible and set to
                  zero
           K  = hydraulic conductivity at content ZK in cm/day (a real
                  variable)
           D  = diffusivity at content Z in cm2/day

Subroutine PR0P may use any method to determine the conductivity and
diffusivity.  Tabular values with an interpolation function or mathe-
matical relationships may be used.  Particularly convenient mathemati-
cal relations are those based on exponential forms.
                                 98

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Exponential Forms:  Semilog

Consider the case where data plotted on semilog paper can be repre-
sented by a straight line as shown  in Figure 15.  Points 1 and 2 are
arbitrary points on the straight line while r is a reference point at
which the unsaturated flow property is Pr.  The equation of the
straight line is:

                log P = log Pr  + slope X  (6-6r)                    [18]

The slope is given by:

                    log P2 - log P! log  (P2/PX)
            slope = - - - - - — —                   [19]
                          (62-61)
Equation  [18]  becomes:

                   P  .  log  pr  .               (e-er)                 [20]
The  conversion from base 10 to  base e logarithms  is:

        Iog10  x =  0.43429 In x    or    Inx =  2.303  Iog10x


Consequently,  equation [20] becomes:


              ln /P \. 2.303  l!!JV!ll (e-8r)                  [21]
 The logarithmic function x=logby is defined as  the inverse of the
 exponential  function and is given by the relationship  y=b* where
 b is the base.   Thus for natural logarithms b=e,  x=lny, and y=ex.
 Consequently,  equation [21] becomes:

                   [2.303 log (P2/Pi)    (e-6r)]
                   -       -—
 The exponent of e can be written as:

                           E « C (8-er)
 where:                C = 2.303 	2—±-                         t24!
                                  99

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              >
              ^-
              
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C is a constant  (essentially the  slope) which is evaluated by select-
ing two points 1 and  2  so that  62>81 and obtaining the 6's and corre-
sponding P values.  In  addition,  a reference point is selected (which
could coincide with either point  1 or 2 if desired) and the values of
6r and Pr obtained.

Exponential Forms:  Log- log

Consider the case where data plotted on log-log paper can be repre-
sented by a straight  line.  The equation of the straight line is:

               fp i         !og (P,/?,)

             lnl    ' 2-303             log (e/v                 [25'
                    [2.303 log  (P2/Pi)            ]
             P=Pr e       - - 2   IJ log  (0/er)                   [26]
                          log  (62/ej)         r


The exponent of e can be written as:

                        E = c  log  (e/er)                           [27]


where:               C = 2.303 1<>g  ^f1^                         [28]
                               log  (Oj/ep                           J

C is evaluated in a similar fashion to that for the semilog form.

Example

The log-log form is often preferable to the semilog form as it usually
results in a better straight line fit.  Several straight line segments
may be required to approximate actual data, regardless of the form.
The following example illustrates use of the semilog form with several
straight line segments.

Measured data defining the moisture-release curve (h vs. 6) and the
conductivity (K vs. 0) are plotted as points on the semilog plot of
Figure 16.  Possible functional relations are shown by the solid
curves.  Diffusivity values were computed by selecting a given 6,
determining K(6), evaluating the slope of the moisture-release curve,
and applying the relationship:

                         D(6) = K(6)                               [29]
                                   101

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                                        ,000,000
                                       500,000
   .002
   .001
     0       O.I      0.2       0.3       0.3"
        0 VOLUMETRIC MOISTURE CONTENT (-)


FIGURE 16.  UNSATURATED  FLOW PROPERTIES
                        102

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Portions of the moisture-release curve  exhibit very steep slopes making
it difficult to evaluate  9h/36.  At best, the procedure is approximate?

The dashed curves represent poor, though possible, approximations of
the functions.  They are  used to illustrate the procedure.  A single
reference point is chosen for the conductivity functions:

              6r = 0.166    where K,. =  1.2 cm/day

Different reference points are chosen for each segment of the diffu-
sivity relationship:

            6r = 0.166    where Dr = 158.75 cm2/day

            6r = 0.255    where Dr = 550 cm2/day

In general, reference points are chosen at the intersection of two
straight line segments.   This assures that values picked from the
curve will produce the same value at the intersection by either rela-
tionship when the equations are used.   Although this is good practice,
it is not absolutely necessary.

In the Fortran coding for subrouting PR0P, it should be noted that the
property relations can be extended below the TD value.  In this case,
the TD value passed in the call list is simply not used.

CAMPBELL'S METHOD FOR DETERMINING UNSATURATED FLOW PROPERTIES

Introduction

Gaylon S. Campbell(23) has proposed a simple method for developing the
functional relationship between the moisture content and hydraulic con-
ductivity.  It is based on a relatively simple form of the moisture-
release curve.  Campbell  found that agreement between conductivities
calculated by this method with those experimentally determined for five
soils was as good as with the Millington-Quirk method.

The soils tested included soils classified as loams, sandy loams, and
sands.  Saturated conductivities ranged from 0.0012 cm/min to 1.12 cm/
min.  Saturated volumetric moisture contents ranged from 0.35 to 0.52.

Because this method is simpler to use than the better known and widely
accepted Millington-Quirk method, its use is appealing.  In addition,
it is easily extended to  include the diffusivity function.

Theory

If a soil sample is saturated with water, the corresponding soil-water
potential is atmospheric.  As water is  removed from the sample, the
                                   103

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potential falls below atmospheric.  Using atmospheric pressure as
the gage reference, the soil water potential is negative.  This is
commonly denoted by referring to them as tensions.

A plot of the soil-water potential as a function of the volumetric
moisture content is variously known as the moisture-release curve,
moisture retention curve, or the moisture characteristic.  If it
can be represented by the functional relationship:
                                 3r
                                \

the hydraulic conductivity is:
                                   2b+3
                        KQ = K-                                 [31]
where:   ty is the soil-water potential               (L)
        $Q denotes ij> at the arbitrary content 0      (L)
        i|»r denotes \J» at the reference level 6r       (L)
         6 is the volumetric moisture content        (L3/L3 or -)
        6r denotes 0 at the reference level r        (L3/L3 or -)
        KQ is the hydraulic conductivity at
             content 0                               (L/T)
        Kj, is the hydraulic conductivity at
             the reference content 0_                (L/T)
         b is an empirical constant determined
             from the data                           (-)

Equation [31] is based on the following assumptions:

   a.  Flow of water in the soil is controlled by the smallest of two
   pores in sequence.

   b.  Only pores that are connected together contribute to the total
   hydraulic conductivity (i.e., isolated and dead-end pores are not
   effective.

   c.  Pores fit together randomly.

Based on these assumptions, the pore radii and pore size distribu-
tion function are used to determine the conductivity.  The pore radii
are related to water contents by the moisture-release curve and the
capillary-rise equation.  A pore interaction term is used to modify
the final conductivity function.
                                  104

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In addition to the conductivity,  solution of the unsaturated flow

equation requires the diffusivity.   It is defined as the conductivity

at a given moisture content divided  by the corresponding slope of the
moisture-release curve:
                                                                [32]




where:  DQ  is  the diffusivity at content 6 (L2/T)



Based on equations  [30] - [32],  the diffusivity becomes:




                                                                [33]
                              6r
The diffusivity at the reference level r can be found from equa-

tion [33]  by setting 6 = 6r.  Then:
                          Dr " -T-^                           [34]
                                 r

Dimensionless  Forms

The preceding  equations are easily recast into dimensionless form
as follows:



                        £•  (tr



                        c-fS-)**'
                        ^    IV

                        n     /«  \ k*2
                        £L.  /1_\                              [37]
                        Dr    ^ry

They are useful in comparing properties of different samples.   Plots
of each dimensionless property on  log-log paper may be inspected for
similarities and differences.
                                105

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Evaluation of Empirical Constant b

It can be shown that a relationship of the form given by equation [30]
will plot as a straight line on log-log paper.  The slope is equal to
the value of the empirical constant b.  The following procedure can be
used to determine b from a set of moisture retention data.

   a.  Plot ^ versus 0 on log-log paper.

   b.  Fit a straight line through the data points.

   c.  Evaluate the fit.  If it is unacceptable, Campbell's method can-
   not be used.  An alternate method such as Millington-Quirk should be
   tried.

   d.  Select two points on the straight line.  (Point 1 corresponds to
   the highest 6.)
   e.  Calculate b by either of the following equations:

                             log OP o/if*,)
   or
b = -
                             log (e2/ei)
                             In

                             In
                                                                   [38]
[39]
   Note that the base of the logarithm is irrelevant and b should
   be a positive quantity.

The 6's in the previous equations are volumetric.   In general, labora-
tory data are reported on a gravimetric basis.

Thus:

       volumetric    -  6 = volume of soil water/total volume of sample

                                                     (L3/L3 or -)

       gravimetric   -  a = weight of soil water/dry weight of soil

                                                     (F/F or -)

It can be shown that:
                       9 = a BD/D
                                 w
[40]
                                 106

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where:  BD = bulk density  of soil  (i.e.,  dry weight  of  soil/unit
               volume  of total  sample)                (F/L3)

        Dw = density of water (i.e.,  weight  of water/unit volume
               of water)                              (F/L3)

Substitution of  equation [40] into equation  [38]  yields:

                              log
                       b  =
                              log
Consequently, determination  of b  can be  based  on  either volumetric or
gravimetric data.  Similarly,  any set of consistent units for the poten-
tials may be used  such  as  centimeters, inches,  feet, or bars* since con-
version from one set  of units  is  merely  ip multiplied by a constant in
which constants in numerator and  denominator cancel.

Significance of Reference  Level r

A specific state,  termed the reference level,  is  noted and used in many
of the previous equations.   Certain  variables  are referenced to this
level, as denoted  by  the subscript r. The  reference level is merely
the moisture level at which  the hydraulic conductivity is known.  Prac-
tically, the saturated  conductivity  K is most  easily measured in the
field or laboratory.  Then

                             Kr = Ks                              [42]

                             6r = 9S                              [43]
Since Dr is computed  from  the  above variables,  it can be excluded.  9S
is the moisture content  at saturation  and  tye  is the corresponding poten-
tial.  ipe is called the  air-entry potential.   Its physical significance
and determination are discussed  in the next section.

Air-entry Potential,  $Q
If a soil is saturated and at  equilibrium with free water at the same
elevation, the pressure  is atmospheric  and  the tension head is zero.
* 1 bar = 1 atmosphere    14.7  lb/in2 which is equivalent to a column of
water = 33.92 feet = 407.1  inches  =  1,033 cm.
                                  107

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Hillel (24) states:

      "If a slight suction, i.e. a water pressure slightly
      subatmospheric, is applied to water in a saturated soil,
      no outflow may occur until, as suction is increased, a
      certain critical value is exceeded at which the largest
      pore of entry begins to empty.  This critical suction
      is called the air-entry suction.  Its value is small in
      coarse -textured and in well -aggregated soils.  However,
      since in coarse- textured soils the pores are often more
      nearly uniform in size, these soils may exhibit critical
      air-entry phenomena more distinctly and sharply than do
      fine-textured soils."

Carefully run laboratory tests on undisturbed samples might provide
a value for i{)e.  This has never been done by the Bureau of Reclama-
tion.  However, a suitable value might be obtained by extending the
straight line of the log-log plot of potential versus moisture con-
tent to saturation.

A review of current literature reveals a lack of numeric values for
the air-entry potential.  However, values should range from 5 to
100 cm depending on the soil texture and pore size distribution.
Lacking field data, the following values are suggested:

                Texture               Range in i|>e
                 sand                    1- 5 cm
                 silt                   10-20 cm
                 clay                   40-60 cm

It is noted that if>e cannot assume a zero value since the relationship
of equation [30] would be meaningless.

The air-entry potential concept is related to capillary forces.  This
suggests the use of the capillary rise equation for cylindrical tubes
for soils on which a mechanical analysis is run.  Based on a water tem-
perature of 25° C (77° F) , an assumed contact angle of zero, and the
previously suggested air-entry values, the following equations are
obtained :

              reff = (10PS +3.3 PSI + Pc)/34,000                  [45]

                ipe - 0.147/reff                                    [46]
                                 108

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where:         reff  =  effective capillary radius of pores  (cm)

        PS> PSI>  PC  =  percent of sand,  silt,  and clay,  respectively,
                         based on the mechanical analysis

                  ij)e  =  air-entry potential (cm)


An effective  capillary tube radius is first computed using equa-
tion  [45].  Since the  larger pores drain first, this equation places
the most weight  on the sands and the least weight on the clays.   The
capillary rise equation [46] is then used to compute the air-entry
value.  If  the soils are of uniform texture,  the following values are
given by the  equations:

                  Texture       reff         ^e
                   (100%)       (cm)        (cm)

                   sand        0.0294         5
                   silt        0.00971       15
                   clay        0.00294       50

There is no provision in equations [45] and [46] to include soil  struc-
ture.   At best,  their use provides approximate air-entry values when
measured  data are lacking.
                                   109

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                           SECTION XI

                USER'S MANUAL - DRAINOUT PROGRAM

INTRODUCTION

This program was designed to predict the response of a subsurface
drainage system consisting of parallel, equally spaced tile drains
to deep percolation inputs.  Both the water table elevation midway
between drains and the drain discharge are computed.  In particular,
this program was developed as part of a water quality simulation
model with the computed monthly drain discharge acting as input to
other programs.

The program may be used in two distinct ways:

   a.  Analysis. - An existing or designed drainage system can be
   analyzed for its response to a given set of deep percolation inputs.

   b.  Design. - Given the porous media properties, depth to barrier,
   effective drain radius, depth to drains, and the deep percolation
   schedule, the drain spacing that will adequately provide the speci-
   fied drainage depth can be determined.

Techniques conform closely to those used routinely by the USER in deter-
mining drain spacings.  Details are given in the program description.

Deep percolation data can be inputed by either of two methods:

   a.  Magnetic tape input of daily values based on the results of
   an unsaturated flow model.  This tape is written by an interface
   program.

   b.  Card input of values based on any desired method. They may
   be developed by considering crop type, agricultural practices,
   climatic conditions, and field experience.

Output includes listed results, an optional magnetic tape for use
with a cathode ray tube plotting routine and optional punched out-
put for use with the drain effluent prediction portion of the water
quality model.  (CRT plotting routines are not included in this
report.)

UNIT NUMBERS

Five input-output devices are referenced by the program:
                                   110

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    Unit                            Unit description
designation                            or purpose

     1         The unit  on  which  the magnetic tape containing deep per-
               colation  data is mounted.  These data are written by the
               interface program  and computed by the Unsaturated Flow
               Program.

     3         The unit  to  which  computed results are written on a
               saved  magnetic tape.  An entirely new tape may be writ-
               ten or results for additional years added to a previously
               generated tape.   It is used in conjunction with the util-
               ity program  to obtain plots of the results.

     5         The common input  tape or unit (CIT).  It is the computer
               system's  standard  input device.

     6         The common output  tape or unit (C0T) 4  ];•£ ^s tfte com-
               puter  system's standard output device.

     7         The punched  card  output device of the computer system.

DATA DECK  STRUCTURE

There are  six  groups  of  input cards in the data deck, as shown in
Figure  17.

Cards in groups  1 through 5 apply to both analysis and design.  Most of
the variables  on these cards are  identical for either use.  However,
certain variables are used  in slightly different ways, others have
unique  restrictions,  and some are not used for design.  These are pref-
aced by an asterisk.   Their use  in design is discussed separately along
with the group 6 card in the section, Design Inputs.

CARD GROUP 1 - Title  Card

  Column       Var    Var                       Variable
    No.      type   name                     description

Card 1  of  1

 1_80          A   TITLE     An 80-character alphanumeric title used
                                 to identify all printed and plotted out-
                                 put.  If this title is desired to be
                                 centered on output, it must be centered
                                 on the card.
                                   Ill

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                                                  Repeat group 5 for each year
                                                   of deep  percolation  data.
                                                     Years deep percolation
                                          /I Years deep percolation
                  Run options  and
                    length
            Porous media properties
     Drain geometry and
       water table  data
 Title  card
FIGURE  17.   DATA  DECK STRUCTURE - DRAINOUT SUBMODEL
                                  112

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  Column
    No.
                                 Variable
                               description
CARD GROUP 2 - Drain  Geometry and Water Table Data

For further clarification,  see Figure 1.  The water table position
referred to by YSTRT, YEST, YLIM, and YTEST means the height of the
water table above  the horizontal centerline of the drains at a point
midway between adjacent drains.
Card 1 of 2

 1-10

11-20


21-30

31-40
41-50
51-60
61-70
71-80
R    SPACE      Drain spacing (feet).

R    D          Distance  from horizontal  centerline  of
                  drain to barrier (feet).

R    ER         Effective radius  of drain (feet).

R    CLSTRT     Amount of deep percolation  added to  the
                  aquifer on the  first  day  (January  1)
                  of the  initial  year of  the run (acre-
                  inches/acre or  inches).   (See RESTART
                  OF PROBLEM.)

R    YSTRT      The  water table position  at the start  of
                  the initial year of the run  (feet).
                  This value can  be negative,  zero,  or
                  positive.   (See NEGATIVE  STARTING  POSI-
                  TION, RESTART OF PROBLEM.)

R    YEST       The  estimated maximum water table posi-
                  tion (feet).   (See SELECTION OF DRAIN-
                  AGE CASE.)

R    YLIM       The  water table position below which the
                  drainout is considered  complete  (feet).
                  When the computed position is below  this
                  value,  it  is  set to zero  for output  as
                  is the  discharge until  another deep per-
                  colation occurs or the  run ends.

R    YTEST      A  test value used to determine when
                  dynamic equilibrium is reached (feet).
                  If the  water  table is within YTEST at
                  the end of successive years, dynamic
                  equilibrium is  assumed.   (See DYNAMIC
                  EQUILIBRIUM.)
                                  113

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  Column
    No.

Card 2 of 2

 1-10
11-20
21-25
 Var    Var                       Variable
type   name                     description
  R    DCSTRT    The value of the cumulative leachate or
                   deep percolation at the start of the
                   initial year when input is via magnetic
                   tape 1 (cm3/cm2 or cm).  (See DEEP
                   PERCOLATION DATA.)

  R    YBLIM     The absolute value of an instantaneous
                   buildup (deep percolation/specific
                   yield) which must be equaled or
                   exceeded before it is applied (feet).
                   (See APPLICATION OF METHOD.)

  I    MXTDR     The maximum length allowed for a drainout
                   period (days).  (See APPLICATION OF
                   METHOD.)
CARD GROUP 5 - Porous Media Properties
Card 1 of 1

 1-10

11-20
  R    PERM      Aquifer permeability (feet/day).

  R    SY        The storage coefficient expressed as a
                   decimal (ft3/ft3 or dimensionless).  It
                   is often taken as the specific yield.
                   It is the ratio of drainable or fill-
                   able voids volume to the total volume.
CARD GROUP 4 _-_ Run Opt ions and Length
Card 1 of 1

 1- 5
       NYRS      The number of years of
                   data to be processed
                   Each year is one file
                   input is by magnetic
                   of group 5 cards when
                   (See ICRDIN below.)
                   NYRS may be zero when
                   is used to calculate
                   table.
deep percolation
for this run.
 on unit 1 when
tape or one set
 input is by cards.
It is noted that
 the N0PT option
the falling water
                                 114

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  Column
    No.

 6-10
 Var    Var
type   name

  I    INFILE
11-15
  I    N0PT
16-20
  I    NREPT
21-25
  I    NSAVE
26-30
  I    NTYPE
                 Variable
               description

The number of the initial file to be
  read on unit 1 when deep percolation
  inputs are by magnetic tape.   (See
  RESTART OF PROBLEM.)

Option to allow calculating drainout
  after the last year of deep percola-
  tion input data.

If N0PT ^ 1, the program stops at the
               end of the last year
               having inputs.

If N0PT = 1, the program continues to
               compute results using
               zero inputs until drain-
               out is completed accord-
               ing to YLIM.

Option to allow repetition of the last
  year's deep percolation input data for
  successive years.  The option is avail-
  able for both card and tape input.
  Note that N0PT may be used in conjunc-
  tion with NREPT.
                               If NREPT *-
                                                       not used.
If NREPT > 0, drainout calculations
  are continued with the  last year of
  input repeated NREPT times, unless
  dynamic equilibrium is  reached.  (See
  DYNAMIC EQUILIBRIUM.)

Option to allow writing of daily and
  monthly results on unit 3.
If NSAVE = 1, data are written.  (See
                OUTPUT.)

Selects the drainage case to be used in
  the analysis.

If NTYPE = 1, analyze as  drains above
                barrier.
                                   115

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  Column      Var    Var                       Variable
    No.       type   name                     description
                              If NTYPE = 2, analyze as drains on
                                              barrier.
                              If NYTYPE = any other value, use the
                                            program criteria to
                                            select the case.
                                            (See SELECTION OF
                                            DRAINAGE CASE.)

31-35          I    IYEAR     The year number corresponding to the
                                initial year being processed in the
                                current run.  It may be 1, 7, 1972,
                                etc., and is used to identify output.

36-40          I    NPUN      Option to allow punching of the average
                                monthly discharge for each year of the
                                run.
                              If NPUN = 1, then punch cards.  (See
                                             OUTPUT.)

41-45          I    INFIL3    The number of the initial file to be
                                written on unit 3.  (See RESTART OF
                                PROBLEM.)

46-50          I    ICRDIN    Option to allow input of deep percolation
                                data by cards.
                              If ICRDIN = 1, then input is by cards,
                                               group 5.

51-55          I    IDESGN    Option to specify the design mode.
                              If IDESGN = 1, the program is to be used
                                               for design.
                              If IDESGN ± 1, the program is to be used
                                               for analysis.

CARD GROUP 5 - Deep Percolation Data (ICRDIN = 1 Only)

Card 1 of ?
11-12
IM0N      Number corresponding to month of appli-
            cation (i.e., January is 1, June is 6,
            etc.).
                                116

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  Column      Var    Var                        Variable
    No-      type   name                      description

13-14          *    IDAT      The  date of the month  of application
                                 (i.e., an application on February  12
                                 is IM0N = 2,  IDAT =  12).

15             A    ADENT     A single alphanumeric  character which can
                                 be used to designate the type or source
                                 of deep percolation  (i.e.,  I  for irriga-
                                 tion,  P or R  for precipitation, etc.)-
                                 It is  printed on output.

16-20          R    AMT       Amount of deep  percolation on the given
                                 date  (acre-inches/acre or inches).

Note:  The IM0N, IDAT, ADENT, AMT  is repeated for each application
with seven values per  card.  The applications need not be in  chrono-
logical order, except  they must be in  groups  by years, with the first
application being first and  the last application being last for each
year.  The end of a year's input is indicated by a blank IM0N, IDAT,
ADENT, AMT set.  If the number  of  applications in a  year is a multiple
of 7, then an additional blank  group 5 card is required.  (See DEEP
PERCOLATION DATA.)  A  perpetual calendar is used so  that no application
should be made on February 29.

The deep percolation inputs  for a  given day are assumed to  occur
throughout the day.  They are applied  as an instantaneous deep perco-
lation at 12 midnight  (i.e., at the start of  the next day).   Conse-
quently, an initial application on the first  day of  the initial year
must be specified by the value  of  CLSTRT (card group 2).

DESIGN INPUTS

The section entitled Design  Method should be  consulted for  clarifica-
tion of the design inputs.

CARD GROUP 2

Card 1 of 2

 1_10          R    SPACE      Initial  trial drain spacing (feet).   If
                                 the Donnan formula is used, SPACE  should
                                 be left blank.
                                  117

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  Column
    No.

51-60
CARD GROUP 4

Card 1 of 1

 1-5
R
VEST
     NYRS
11-15
16-20
     N0PT
     NREPT
21-25
31-35
36-40
     NSAVE
     IYEAR
     NPUN
                 Variable
               description

The design maximum water table position
  (feet).
          The number of years of deep percolation
            data to be processed for this run.  For
            design, only a single year of inputs is
            allowed.  Therefore, NYRS must equal 1.
            (See INPUT CHECKS AND ERROR MESSAGES.)

          This option has no significance when the
            design mode is being used and is ignored.

          The maximum number of years allowed to
            reach dynamic equilibrium for one trial
            spacing.  (See INPUT CHECKS AND ERROR
            MESSAGES.)

          For design, only the results for the cor-
            rect drain spacing (i.e., the designed
            spacing) at dynamic equilibrium are
            available for output.  If the spacing
            is not determined, there are no water
            table or drain discharge results.
            Therefore:

             NSAVE. - The daily and monthly
               results at dynamic equilibrium
               for the designed system are writ-
               ten on unit 3 when NSAVE = 1.

             IYEAR. - The year number associated
               with the results at dynamic
               equilibrium.

             NPUN. - The average monthly discharge
               values for the designed system at
               dynamic equilibrium are punched when
               NPUN = 1.
                                118

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  Column
    No.

41-45
 Var
type
 Var
name

INFIL3
                 Variable
               description

The number of the initial file to be
  written on unit 3.  It is noted that
  multiple files may be written on unit 3,
  even though each file represents a dif-
  ferent drainage system.
CARD GROUP 6 - Design Data (IDESGN = 1 only)

Card 1 of 1
 1- 5



 6-10


11-15


16-20


21-25

26-35
  I

  R
36-45
  R
IM0NST    Number of month corresponding to start
            of period from which SEEP is computed
            (i.e., January is  1, June is 6, etc.).

IDATST    The date corresponding to the start of
            period given by  IM0NST.

IM0NFI    Number of month corresponding to end of
            period from which  SEEP is computed.

IDATFI    The date corresponding to the end of
            period given by  IM0NFI.

NTRYMX    Maximum number of  trial spacings allowed.

YCHECK    The absolute value of the difference
            between the computed maximum rise at
            dynamic equilibrium and the design
            value YEST which cannot be exceeded
            when the drains  are properly spaced.

SEEP      Steady-state seepage rate to be used
            when the Donnan  formula is used for the
            initial spacing  (feet/day).
SELECTION OF DRAINAGE  CASE

The USBR drainage  design procedures make use of the two limiting cases:

   a.  Drains an infinitely long way above an impervious barrier.

   b.  Drains resting  on an impervious barrier.
                                  119

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Any real system must fall between these extremes.   Based  on  experi-
ence, the USER has found the following criteria useful  in selecting
the appropriate case:

   a.  D/YEST^ 0.1, analyze as drains on a barrier.

   b.  D/YEST - 0.8, analyze as drains above a barrier.

   c.  0.1<  D/YEST < 0.8, analyze both ways and use the
   results with discretion.   (The program analyzes  this case as
   drains above a barrier.)

Here, D is the distance from the horizontal centerline  of the drain
to the barrier, and YEST is the maximum water table rise  above  the
drains at the midpoint between drains.

Although the criterion of (c) is not particularly satisfying, it is
a practical recommendation since the drainage system may  mathematically
approach both limiting cases at different times.  Improved accuracy
dictates use of the nonlinear solutions of Moody.(11)

The value of YEST is an input.  Since the true value is unknown until
the analysis is completed, the input value is only an estimate  (or
the design value when in the design mode).  If an estimate is not
made and YEST is less than or equal to 0.01 foot (essentially zero),
the ratio D/YEST is presumed unknown.  The value of D is  then used to
select the case - if D is equal to or greater than  1.0  foot, analysis
is for drains above a barrier.

The program criteria can be overridden by means of the  input variable
NTYPE.  A value of 1 selects the case of drains above a barrier while
a value of 2 selects the case of drains on a barrier.   Use of this
variable permits analysis by both cases in the intermediate range,
though this must be done by separate runs.

The flow chart of Figure 18 summarizes the selection process.

Note that it is possible to specify an analysis by the  wrong method
according to either criteria  (a) or  (b).  This situation  is noted on
output, as is a recommendation that the intermediate range be analyzed
as both cases.  The method of analysis, how it was selected, and the
recommended method of analysis based on the computed results are
printed on output, both for design and analysis.
                                  120

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                                             Anyother
             DRAINS
               ON
               THE
             BARRIER
FIGURE 18. PROGRAM CRITERIA TO SELECT DRAINAGE CASE
                          121

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APPLICATION OF METHOD

Two problems arise in using the USBR drainage methods:(   )

   a.  Use of a linear solution for long drainout periods  over-
   estimates the water table decline.

   b-  Reinitializing the water table when an instantaneous
   buildup occurs introduces volumetric errors because of  the
   mathematics involved.

The latter problem is insignificant for semiarid areas where deep per-
colation occurs at intervals of 10 days or more.  It is serious  for
humid areas where deep percolation from precipitation occurs fre-
quently, or when unsaturated flow results are used on a daily basis
(as when magnetic tape input via unit 1 is used).  Errors  in the mass
balance of the saturated system are the best indicators of this  dif-
ficulty.  The solution is to increase the short drainout periods by
combining several days of deep percolation into a single application.

The program implements this approach by means of the input variable,
YBLIM.  If the deep percolation on a given day is not sufficient to
attain this value, it is accumulated and drainout proceeds.  The next
buildup is added to this accumulated value and the sum is again  com-
pared to YBLIM.  The process continues and is repeated as necessary.
By using a larger value of YBLIM, the short drainout periods are
lengthened and mass balance usually improves.  Rather than specifying
a minimum drainout period, the above approach was used because it is
more responsive to variations in the deep percolation inputs during a
run.

Since deep percolation inputs may produce either an instantaneous
buildup or decline, it is the absolute value of the accumulated  deep
percolation that is compared to YBLIM.  If YBLIM is left blank or
set to 0, the program uses an internally set value of 0.1 foot.

The first problem of long drainout periods is corrected by subdivid-
ing these periods into two portions.  A zero buildup is assumed, the
water table is reinitialized, and the drainout process begins again.
There are two means available in the program to accomplish this:

   a.  The maximum allowable length of a drainout period in days can
   be specified on input by MXTDR.  If a drainout period reaches this
   length, reinitialization occurs.  If MXTDR is left blank or set to
   0, the program uses a preset value of 60 days.
                                  122

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   b.   A fictitious, near zero, deep percolation  can  be  added  on
   the day when reinitialization  is desired.  This  approach  is use-
   ful when input is by cards, but cannot be used with tape  input.
   The magnitude of the application must be sufficient to  exceed
   the value of YBLIM which, as noted  above, cannot be set to  zero
   exactly.  In general, if SY is the  specific yield, the  required
   value is YBLIM x SY x 12 inches.  When the value of YBLIM is
   not important (the usual case  when  input is by cards),  the  val-
   ues of YBLIM and MXTDR can be  chosen to insure the desired  result.
   For example, if YBLIM = 0.0001 foot and SY = 0.1,  a fictitious
   application of (0.0001) (.1) (12) = 0.00012 inches is used  on the
   desired dates.  The value of MXTDR  is then set to  a large value
   (say 365) to assure it does not shorten the desired drainout
   period.

DYNAMIC EQUILIBRIUM

If the same annual set of deep percolation inputs is  used  for  succes-
sive years, the drainage cycle will approach a repeating annual pat-
tern.   When this repeating cycle  is attained, "dynamic equilibrium"
is said to have been achieved.  It is  this condition  for which the USER
designs drains.

A convenient test for dynamic  equilibrium is based  on the  comparison
of the water table position for successive years  at the  same time
within the annual cycle.  Year-end values are practical  for  this pur-
pose,  and the variable YTEST is read for the test.  Its  value  can be
picked to obtain as strict a tolerance as desired.  The  smaller the
value, the more cycles required to satisfy the test.

In the program, testing for dynamic equilibrium does  not occur until
all years of deep percolation  inputs have been read  (NYRS) and the
repetition mode is being used  (NREPT > 0).  Computations terminate
when the year-end water table positions are within YTEST.

DEEP PERCOLATION DATA

There is no restriction on the sign of the deep percolation  inputs.  A
positive value denotes water being added to the saturated  system while
a negative one denotes water being removed.  The  latter  case results
when unsaturated flow phenomena are explicitly used and  evapotranspira-
tion produces upward flow.

The program allows deep percolation inputs on a daily basis.   Deep per-
colation occurring on a given  day is assumed to be  applied at  the end
of the day (at the start of the next day).  For example, an  application
on June 6 is applied as an instantaneous buildup  or decline  at the
start of June 7.
                                  123

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Computations are performed day by day for an entire year.   Partial
years are not allowed.  Deep percolations read from cards  include the
date on which they occur.  All other days are assumed to have  zero
inputs.

Tape input using unit 1 is on a daily basis, starting with  some  initial
day and ending with some final day.  Days preceding the initial  or  fol-
lowing the final are assumed to have zero inputs.  Organization  of  the
tape is shown in Figure 19.  Because this tape is also used for  plot-
ting unsaturated flow results, it contains information not  needed by
the drainout program.  In particular, only the Julian day and  the cum-
ulative leachate are used.

The cumulative leachate refers to the accumulated amount of water that
was leached from the unsaturated into the saturated system.  The drain-
out program uses the cumulative amounts on successive days  to  compute
the deep percolation by taking the difference.  Since the drainout  pro-
gram can be restarted and may be run using data starting with  a  year
other than the first, the initial cumulative leachate for computing
the first day's input is required.  This is inputed by the  value of
DCSTRT.  Once the program is running, the cumulative values are  car-
ried automatically.

The correct starting year is selected by means of the input variable
INFILE, described in the next section.

NEGATIVE STARTING POSITION

The water table position at the start of the initial year of the run,
YSTRT, may be specified as negative.  A horizontal water table is
assumed as long as it is at or below the drain level.

Logically, use of a negative starting position is limited to the
analysis mode.  The gradual buildup of the water table to the  drain
level can then be followed.  For design, a negative YSTRT merely
wastes computer time since the dynamic equilibrium condition is
required for design.

The following minor modifications to the computations and output are
noted:

   a.  Although mass balance results are printed, the water in stor-
   age above the drains will be negative.  It does not represent a
   true quantity of water since the drain acts as the reference
   level.  However, the change in storage during the year is correct.
                                  124

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B0T (beginning of tape,
  load point)
                              -E0F (end  of
                                 file  mark)
            L
            h i ghday
1  record/day,  starting
 ow day,  ending at hi ghday
  1  f i le/year ,  1st year
                                    2nd year
                                                     3rd year    etc
Each dai Iy  record i s
  WRITE (2)  I  YEAR,
        SF(J),  U(J),
Z(J),
where
  1  YEAR
  I I
  XT

  CL
  DEFAMC
  Cl
  HED

  ETS

  N
  J
  TN(J)
  Z(J)
  SF(J)
  U(J)
                  s
                 i s
                 is

                 is
                 is
                                           statement:
                                           ETS,  N,  (TN(J),
    written  by  the  binary write
   II,  XT, CL,  DEFAMC, Cl, HED,
    J = 1,N)
   the  year  number
   the  JuI ian day
   the  decimal  part  of the day (will always be
   iO  for  end of  day)
   the  cumulative  leachate from unsaturated zone (cm)
   the  cumulative  evapotranspirat ion that could
  not  be supplied  to the  crop  because of low
  moisture contents  (cm)
is the  cumulative  infiltration at the surface (cm)
is the  amount of  water at the  surface, remaining
  to infiltrate (cm)
is the  net amount  of water which  has passed
  through  the surface  in  either direction(cm)
is the  number of  nodes  in the  column
is the  particular  node number
is the  volumetric  mositure content  (d imens i onless)
is the  evapotranspiration not  supplied since the
  last  output time  on  tape 5  (see unsaturated flow
  program) (cm)
is the  amount of  water that has moved between
  node  J and J  1  since the last output time on
  tape  5 (cm)
is the  evapotranspirat ion rate (cm/day)
FIGURE 19.  ORGANIZATION-DAILY MOISTURE  TAPE
                          125

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   b.  The adjustment factor for daily discharges does not  apply
   when there is no discharge during the year.  Therefore,  the
   message ADJUSTMENT FACTOR NOT REQUIRED appears.

   c.  Analysis of the drainage case is meaningless when  the water
   table is always below the drains.  Therefore, both analysis  and
   output are deleted.

RESTART OF PROBLEM

A design problem cannot be restarted by this method.  This  section  only
applies to analysis.

CLSTRT has been defined as the amount of deep percolation to be added
on the first day of the initial year of the run.  As noted  in the
previous section, deep percolation occurring on a given day is  applied
at the start of the next.  Therefore, an input on December  31 of the
previous year is carried over and applied on January 1.   To allow for
this carryover on the initial year of the run, its value  must be read.
The carryover for subsequent years is automatic.  On completion of  a
run, the value of CLSTRT for the next year is printed.  It  includes
the actual deep percolation of December 31 plus any accumulated deep
percolation not yet applied due to use of YBLIM.  (See APPLICATION OF
METHOD, p. 122.)

The water table position at the end of the run is also printed.  It
should be used as the value of YSTRT if the problem is restarted for
the next year.

When a problem is restarted, it is necessary to position  the input and
output tapes on units 1 and 3 for the first operation if  they are used.
This is accomplished by means of the inputs INFILE and INFIL3.   INFILE
is the initial file to be read on unit 1 while INFIL3 designates the
first file to be written on unit 3.  Since each file corresponds to a
single year's data, the word file is synonymous with year.

The program skips over (INFILE-1) or (INFIL3-1) files and positions
the tape at the start (first record) of the initial file.   For  the
first run of a problem, the file numbers may be set to 1  or left blank.
For subsequent runs, they must be set correctly.  As an example:

   a.  Input tape 1 contains 3 years of data, with the third year
   representing an average annual input to be used for subsequent
   years.

   b.  The initial run computed results for 5 years.
                                 126

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   c.  To restart the problem at  the  6th year,  INFILE =  3  and
   INFIL3 = 6.

DESIGN METHOD

The determination of the proper drain spacing  is  a  trial-and-error
process.  An initial spacing is selected and the  response  of the
drainage system to the deep percolation inputs  is analyzed.  The
maximum water table rise at dynamic equilibrium is  then  compared
with the design value.  If the computed rise is greater, the drains
must be spaced closer while a smaller computed  rise means  the drains
may be spaced farther apart.

Special considerations for design include:

   a.  Selection of the initial spacing.

   b.  Criteria for deciding when an  adequate  design has been found.

   c.  Method of adjusting the trial  spacings  to  arrive  at the
   design spacing.

Each of these items is now discussed.

Design Method - Selection of Initial  Spacing

There are two alternatives available  to the program user:

   a.  The initial spacing can be specified on  card 1 of group 2 as
   SPACE.  This may be based on experience, a rational analysis, or
   pure guess.

   b.  The steady state Donnan formula can be used.  This  formula
   makes use of a steady deep percolation rate  (seepage  across the
   water table).

In practice, the steady-state seepage rate, SEEP, is usually based
on the deep percolation from one  irrigation averaged over  the time
between irrigations during the peak of the irrigation season.  As
such, it represents a maximum rate at which water must be  drained
in order to provide a sufficient  drainage zone.  Experience has
shown that when drains are on the barrier, this rate may be halved.

The steady seepage rate can be specified by the input variable SEEP
on the group 6 card.  Alternately, the user may specify  the starting
(IM0NST, IDATST) and ending  (IM0NFI,  IDATFI) inclusive dates for a
period over which the average seepage rate is  computed.  The total
                                 127

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deep percolation for the period is used with the length of  the
period to compute SEEP.  If the starting date is not specified,
it is taken as January 1 while December 31 is used when the ending
date is not specified.

In summary:

   a.  If SPACE > 0, it is used as the initial spacing even though a
   value of SEEP or the period dates are specified.

   b.  If SPACE - 0, the Donnan formula is used.

When the Donnan formula is used:

   a.  If SEEP * °» i1: is used-

   b.  If SEEP is - 0, the seepage rate is based on deep percolations
   during the period IM0NST, IDATST through IM0NFI, IDATFI.  If the
   dates are not specified, the period is taken as January 1 through
   December 31.

Design Method - Criteria of AdequateDesign

The design maximum rise is given as YEST on card 1 of group 2.  If
the computed maximum rise at dynamic equilibrium is YMAX, the design
is deemed adequate when the absolute value of (YMAX - YEST) is less
than or equal to YCHECK.  Here YCHECK is the tolerance read from the
group 6 card.

If YCHECK - 0, the program uses a default tolerance of 0.5 percent
of YEST.  Thus, if YEST =4.0 feet, YCHECK =0.02 feet.  Should
YCHECK < YTEST (the value used to determine when dynamic equilibrium
is reached), it is probable that an adequate design will not be found.
This is particularly true if YCHECK is much smaller than YTEST.  To
avoid this possibility, the program resets YCHECK to YTEST if
YCHECK < YTEST.

The maximum number of trial spacings is specified as NTRYMX on the
group 6 card.  If a satisfactory design is not obtained after NTRYMX
trials, a message is printed and execution terminates.  When NTRYMX is
not specified, a program default value of 20 is used.  This is also
the maximum value.  Should the user specify NTRYMX > 20, the program
resets it to 20.

Design Method - Spacing Algorithm

When the first trial design is finished, the program uses the YCHECK
criteria to determine whether an adequate design has been found.  If
                                 128

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it has not, the spacing  is  either  doubled  or  halved  depending  on  the
results.  If the spacing is  doubled,  it  must  also  meet  the  requirement
that the new spacing be  at  least  100  feet.  This procedure  is  contin-
ued until spacings both  greater and smaller than the correct design
are found.  With the correct spacing  bracketed, the  computed maximum
rises are used in conjunction with the design value  and linear inter-
polation to obtain future trial spacings.

Normally, three trials result in  the  correct  spacing.   Thus, the
initial spacing is not critical.

INPUT CHECKS AND ERROR MESSAGES

A number of logical checks  are made on the input data.   Failure to
meet any of the tests results in  an error message.   These messages
are listed and explained in  the next  subsection.   They  are  prefaced
by the notation:

            ********  ERRORS IN INPUT DATA  ********

In addition, either of the  following  messages may  appear when  the
design mode is used:

         * MAXIMUM NO. TRIALS REACHED, SPACING NOT FOUND

         * DYNAMIC EQUILIBRIUM NOT REACHED, TERMINATE **

The first message results when the limit NTRYMX is reached  without the
spacing being determined according to the YCHECK criteria.  The second
message is obtained when dynamic  equilibrium  is not  reached using the
YTEST criteria by NREPT  years.

Should any of these errors be detected,  the termination message:

            ********  EXECUTION TERMINATED  ********

is written.  When a normal  termination is  obtained after all computa-
tions are finished, the  message:

     ********  COMPUTATIONS  FINISHED.  NORMAL EXIT.   ********

is written.

OUTPUT

Program output consists  of printed listings,  punched cards, and com-
puted results written on magnetic  tape.
                                  129

-------
Printed data listed by the program on unit 6  is  standard  output.
It includes:

   a.  Input data read from cards including deep percolation inputs
   when ICRDIN = 1.

   b.  A mass balance summary for each year of the run.

   c.  The volume of water removed by the drains for  each day along
   with monthly and annual values as well as  the percent  each month
   is of the annual total.

   d.  The water table position for each day, as well as  the mini-
   mum and maximum rises  and their dates.

   e.  The restart parameters YSTRT and CLSTRT for future years.

   f.  The method of analysis (case) used as  well as  the  recommended
   case.

Punched card output is written on unit 7 by the  program.   This  out-
put is optional, being selected by NPUN =1.  It consists of a title
card identical to the group 1 card on input followed  by pairs of
cards containing monthly  drain discharge volumes for  each year of
the run (or dynamic equilibrium year for design).  The volume cards
have the form

                IYEAR, ICRD, (QM0N(I), I = 1, 6)

punched using an I5,I2,6E12.5 format.  Here

   a.  IYEAR is the year  number.

   b.  ICRD is the card order within the year.   ICRD  = 1  contains
   data for the first 6 months and ICRD = 2 contains  data for the
   second 6 months.

   c.  QM0N(I) are the individual monthly volumes.

This card output is intended for use as input to the  drain effluent
prediction program (DE0200) of the irrigation return  flow quality
model.

Computed results are written by the program on unit 3 as  optional
output when NSAVE = 1.  Each year's output is one file on unit 3.
                                  130

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Four logical records are written  in  each  file  as  shown  in Figure  20
These include:

   a.  Title information,  the  date of  the computer run, and the
   year number of the computed results.

   b.  Daily water table position.

   c.  Daily discharge volumes.

   d.  Monthly discharge volumes  and the  annual value.

All data is written without format in  binary form.  The magnetic
tape is intended as input  to the  utility  program  UT06 which plots
computed drainout results  on a cathode ray tube.

Logical Error Messages

The following is a complete list  of  error messages:

   EMI - DRAIN SPACING = ? LE 0.0
   EM2 - DESIGN MAX RISE = ?   LE  0.0
   EMS - NO. YEARS OF DEEP PERC.  INPUTS = ?  MUST BE 1 FOR DESIGN
   EM4 - DEPTH TO BARRIER  = ?  NEGATIVE
   EMS - EFFECTIVE RADIUS  = ?  LE 0.0
   EM6 - PERMEABILITY = ?  LE  0.0
   EM7 - STORAGE COEFFICIENT = ?  LE 0.0  OR GE 1.0

EMI applies only to analysis,  EM2 and  3 only to design, while the
remainder apply to both design and analysis.   Each is discussed below:

   EMI - The drain spacing SPACE  must  be  specified as a nonzero
         positive quantity for analysis.

   EM2 - Drains cannot be  designed unless the  design rise YEST is
         specified as a nonzero positive  quantity.

   EMS - Only a single design  year of  deep percolation inputs, NYRS,
         is permitted.

   EM4 - The drains must rest  on  or  be above the  barrier material;
         hence, D must be  zero or positive.

   EMS - The drains must have  a finite effective  radius, ER.

   EM6 - The permeability, PERM,  must  be  a nonzero positive quantity.

   EM7 - The storage coefficient, SY,  must exceed zero if a transient
         solution is possible  and must not equal  unity by definition.
                                 131

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B0T  (BEGINNING OF TAPE)
                                                 E0F (END OF FILE MARK)
                                                         oc
  LOGICAL RECORD
LOGICAL RECORD 2   LOGICAL RECORD 3    LOGICAL RECORD 1
                                                                            h- O
                                                                            •< «t
                                                                            LU LU
                                                                            O_
                                                                            LU Q£
                                                                            ce o
                 J I
             J  I
J L
                AIDENK I )
                NDATE
                IYEAR
               QMQN( I )
               QYR
J
(AIDENT (I), 1=1,10),    (Y(l),  1=1,365)     (Q(I),1=1,365  (QMQN(I), 1=1,12),  QYR
   NDATE,  I YEAR
                                  NOTATION
                            80  character  alphanumeric title
                            date  of  the  computer run
                            year  number  of  computed results
                            water  table  position for Julian day  I
                            daily  drain  discharge for Julian day  I
                            monthly  drain  discharge for month  I
                            annual drain  discharge for year  I  year
   FIGURE 2O.  ORGANIZATION  OF  MAGNETIC TAPE OUTPUT
                      DRAINOUT SUBMODEL

-------
                           SECTION  XII
                         USER'S  MANUAL
                INTERFACE  FOR  CHEMISTRY  PROGRAM
INTRODUCTION
This program converts data  generated  by the  Unsaturated  Flow Sub-
model to forms suitable  for input  to  the Unsaturated Chemistry and
Drainout Submodels.

The conversion for Unsaturated  Chemistry involves  a transfer from
a nodal concept in Unsaturated  Flow to  a segment concept in Unsatu-
rated Chemistry.  Soil water flux  and content values at  each node
are transformed to  (1) mean or  representative flux values at the
upper and lower boundaries  of each soil segment and  (2) mean or
representative soil water contents for  each  segment  (segment vol-
umes) .  This procedure is repeated for  each  time step being used in
Unsaturated Chemistry.   A commonly used time increment in 0.1 day.

At the end of each day,  Interface  can write  binary information to
unit Tape 2.  This information  for Drainout  is similar to the data
read from input unit Tape 3 with the  exceptions that Q has been
added, and DEFAMC and K  have been  deleted.   Additional information
can be found in the DATA DECK STRUCTURE and  TAPE OUTPUT DETAILS
sections.

The current version of the  Interface  Program is designed to convert
data from 21 moisture nodes to  data suitable for 10 soil segments
plus one segment to account for water applications at the surface.
A more generalized program  could be developed at a future date.
However, it is possible  to  modify  the program for  other nodal and
segment combinations provided a few relationships  are considered.

In general, a workable procedure is to  determine the number of
soil segments needed based  on dispersive considerations and then
compute the number of nodes to  be  used  in Unsaturated Flow from
the equation:

                No. Nodes = No. segments * N +1                  [47]

Where:

                         N = 1,  or  2 or  3 .  . .

            No. segments =  the  number of soil segments not counting
                            the  segment  for surface applications
                                 133

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It is not recommended to use a value for N less than 1.   Increasing
the magnitude of N increases the number of nodes, thus increasing
the accuracy and computer execution time of the Unsaturated Flow Sub-
model.  Using 10 soil segments, values for N of 2 or 3 have proven
to be adequate.

The number of terms in the equation for segment volume given  in the
Interface Program listing (card label, INTG 250) is given by

                        No. Terms = N +1                            [48]

The first and last terms carry half the weight of the remaining ones.
The sum of the weighting fractions must equal the segment length in
cm.  Segment length is computed by

         Seg. Length (cm) = Length of Soil Column (cm)              [49]
                                  No. segments

The "DO Loop" parameters (Card label, INTG 230) must be set as follows:

   First Parameter  - equals 1
   Second Parameter - equals N*(No. segments - 1)  +1
   Third Parameter  - equals N

The "DO Loop" parameters (card label, INTG 280) must be set as follows:

   First Parameter  - equals N +1
   Second Parameter - equals N*(No. segments - 1)  +1
   Third Parameter  - equals N

Implied "DO Loop" termination in write (1) statement must be  changed
to correspond to number of soil segments +1.

The card labeled INTG 350 must be set as follows:

                       MOISIN(M) = SF(M1)

   where:  M equals the number of segments +2.
           Ml equals the number of nodes -1.

UNIT NUMBERS

Five file units are used by the Interface Program.  Tape  3 is under-
stood to contain the binary output data written by the Unsaturated
Flow Submodel.  Unsaturated Flow writes this data set out to  Tape 5,
and Interface accepts it as input on Tape 3.
                                   134

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Interface writes binary output  to  Tape  1  which is  read by Unsaturated
Chemistry on unit Tape 1.   Binary  output  data may  be written to Tape 2
in a form suitable for input  to the  Drainout Submodel via its Tape  1.

In addition, use is made  of the common  input and output file units.

DATA DECK STRUCTURE

Data from two basic card  groups are  read  from the  common input file.
These groups contain  title  and  control  information.
CARD GROUP 1 - Title  Information
   Column
     No.
 Var   Var
type  name
Card 1 of 1

1-80         A
      AID
               Variable
             description
Title or heading information used
  to identify problem.  Title is
  printed on output.
CARD GROUP 2  - Control  Information
1-5
6-10
      IPRINT
11-15
16-20
21-25
26-30
31-35
36-40
41-45
I
I
I
I
I
I
I
INFILE (1
INFILE (2
INFILE (3
IRECB (1)
IRECB (2)
IRECB (3)
LSFILE
The number of moisture nodes used
  in Unsaturated Flow Submodel.

Print interval for output listing
  of data being written to Tape 1.
  Value does not affect write inter-
  val to Tape 1.

Initial file to use on Tape 1

Initital file to use on Tape 2

Initial file on unit Tape 3

First record initial file on
  unit Tape 1

First record on initial file on
  unit Tape 2

First record on initial file on
  unit Tape 3.

Last file for unit Tape 3
                                  135

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   Column
     No.
 Var   Var
typ_e_  name
46-50

51-55


56-60
      IRECB

      NOREC


      NSAVE2
               Variable
             description

Last record for unit Tape 3

No. of records in full file on
  unit Tape 3.

If = 1, Tape 2 is written in form
          suitable for input to
          Drainout Submodel.
If = 1, Tape 2 is not written.
TAPE OUTPUT DETAILS
Tape 1 - Output to Unsaturated Chemistry Submodel
WRITE (1)  (IYEAR), II, INT, JDUM, SEGVOL (J) MOISIN (J), MOISONT
  (J), TEN, U(J), J=l, 11)
  Variable
    name

IYEAR

II

INT

JDUM


SEGVOL (J)
MOISIN(J)


MOISOUT(J)


TEN
                                 Variable
                               description

                   The year number.

                   The Julian day number.

                   The time step within each day.

                   A dummy variable reserved for
                     future use.

                   The volume of water (cm3/cm2) con-
                     tained in each soil segment, J.
                     Note:  Segment SEGVOL  (1) contains
                     water ponded on soil surface.

                   The flux of water (cm3/cm2) across
                     the upper boundary of  segment J.

                   The flux of water (cm3/cm2) across
                     the lower boundary of  segment J.

                   A dummy value for soil water tension
                     set equal to 300 cm water.  Values
                     for TEN must be computed for each
                     segment in some applications of
                     Unsaturated Chemistry.
                                136

-------
  Variable                                     Variable
    name                                     description

U(J)                             The consumptive use of water
                                   (cm3/cm2/day) for segment J.
                                 Note:   If uptake of NH4+ and
                                   N03~ is taken to be propor-
                                   tional to consumptive use,
                                   then U(J) must be expressed
                                   in terms of cm3/segment/time
                                   step.

Tape 2 - Output  to  Drainout Submodel
WRITE  (2) IYEAR,  II,  XT,  CL, CI, HED,  ETS, Q, (TN(J), Z(J), SF(J),
  U(J), J=1,Q)

IYEAR                            The year number.

II                               The Julian day number.

XT                               The fraction of a day when the  data
                                   were written (e.g., 0.1 day,  0.2  day,
                                   etc.)

CL                               Cumulative deep percolation (cm3/cm2)

CI                               Net infiltration from applied water and
                                   errors in handling the upper  boundary
                                   (cm3/cm2).

HED                              Water standing at surface (cm).

ETS                              Total quantity of water crossing
                                   surface boundary (cm3/cm2)

Q                                Number of moisture nodes.

TN(J)                            Volumetric moisture content (cm3/cm2)
                                   at time XT for Node J.

Z(j)                             Deficit moisture (cm3/cm2) at Node  J
                                   during the last time interval written
                                   to Tape 5 by Unsaturated Flow.
                                137

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  Variable                                    Variable
    name                                    description

SF(J)                           Total soil water flux (cm3/cm2)
                                  between Node J and (J+l) during
                                  the last time step written to
                                  Tape 5 by Unsaturated Flow.

U(J)                            Evapotranspiration rate at Node J
                                  (cm3/cm2/day).
                                  138

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                          SECTION XIII

                          USER'S MANUAL

                  UNSATURATED CHEMISTRY PROGRAM

INTRODUCTION

The purpose of this manual is to provide the user with detailed oper-
ating instructions for the Unsaturated Chemistry Program.  The manual
is written with the assumption that the user has read the sections of
this report and related references pertaining to the program's con-
cepts and theoretical basis.  The manual includes specific discus-
sions of the types of data needed to run the program.  Use or gener-
ation of all input and output media such as printed output, data cards,
magnetic tapes, and disks is discussed in detail.

The source program is written in FORTRAN IV computer language for a
Control Data Corporation CYBER 74-28 machine.  The program as compiled
under the Fortran Extended Compiler requires 105K octal to load and
75K to execute.

CARD GROUPS

The basic card groups needed to run the program are illustrated in
Figure 21.  Those groups marked with a dot must be omitted from the
deck when the nitrogen portion of the model is bypassed  (NBYPAS = 1).
Group 6.5 must be included in the deck when the salt portion of the
model is bypassed (SBYPAS =1).  At all other times, group 6.5 is
omitted.

In a similar manner, group 7 is included in the deck only when flow
data are to be read from cards (ITEST = 1).  When ITEST = 0, flow
data are read from tape 1.

Group 8 contains the initial soil analysis and must be present when
the program is started from time zero (IRERUN = 0) .  When IRERUN = 1,
group 8 is deleted from the deck.

Group 9, the restart data, is punched by the program at the conclu-
sion of a run provided IPUNCH = 1.  Group 9 is read into the program
and must be present when IRERUN = 1 and IREADP =1.  If IRERUN = 1,
but IREADP = 0, group 9 is not included, but tape 3 containing the
restart data must be present.  This tape is written whenever
IPUNCH * 0.
                                   139

-------
                                                           Group *I6 Crop
                                                            uptake of nitrogen
                                                     /Group* 15 Root
                                                         distribution
                                                     Group* 14 Organic
                                                      nitrogen applications
                               Group* 13 Fertilizer applications
                         ,/Group *I2  Irrigation water
                            application dates
                  Group*ll  Organic nitrogen
                   application dates	
            /Group* 10 Fertilizer
                 application dates
            Group *9 Restart data
         Group *8  Initial soil analysis
      Group*?  Flow  data
/Group*6.5 Salt by-pass data
            / Group *6 Irrigation  water  .
                analysis
                                Group *5  Temperature data
         //Group*4  Constituent  horizon
              depths
Group *3  Temperature horizon
 depths
         Group *2  Control cards
   /Group* I  Title  card
          FIGURE  21.  CARD GROUPS IN UNSATURATED
                       CHEMISTRY  SUBMODEL
                                     140

-------
CARD GROUP 1 - Title Card
  Column
    No.
 Var    Var
type   name
Card 1 of 1

 1-80        A      TITLE

CARD GROUP 2 - Control  Cards

Card 1 of 3

 1-5        R      DELX
 6-10
21-25
26-30
31-35
36-40

41-45
 R
 R
 R
 X

 R
DELT
11-15         X

16-20         R      CH
       CHI
AL
A2
PK
                           Variable
                          description
                  Any  title  desired  on printed output.
Soil segment size (cm).  See page 145 for
  details.

Time interval size (days) corresponding
  to intervals for moisture flow on tape 1,

Not used by program.

Convergence criterion for nitrogen trans-
  formation subroutine.  See page 145 for
  details.  Suggested values are in the
  range 0.1 - 10.0 p/m nitrogen.

Convergence criterion for ion exchange
  subroutine.  See page  145 for details.
  Suggested values are in the range
  1 x 10"2 - 1 x 10~6 moles/liter.

Shutoff criterion for nitrogen trans-
  formation subroutine.  See page 145 for
  details.  Suggested values are in the
  range 0.1 - 2.0 ug/soil segment/time
  step.

Shutoff criterion for ion exchange sub-
  routine.  See page 146 for details.
  Suggested values are in the range
  1.0 - 5.0 ug/soil segment/time step.

Not used by program.

Fraction of total plant uptake of nitro-
  •gen as N03-N.  A suggested value is
  0.95.  As NOi-N mass -*• 0.0 plant uptake
  of NOi-N -»• 0.0 regardless of plant
  uptake imposed on system.
                                    141

-------
  Column
    No.

46-50
 Var    Var
type   name
 R
PK1
51-55
 R     FACT
Card 2 of 3

 1-5        I     LL
 6-10
11-15
16-20
21-25
26-30
31-35
36-40
       MM
       0
       CR0P
       T0
       NT
       IPRINT
       JPRINT
                Variable
               description

Fraction of total plant uptake of nitro-
  gen as NH^-N.  A suggested value is
  0.05.  Fraction as N03-N plus fraction
  as NH^-H must equal unity.  The same
  relationship for N03-N holds for NHH-N
  uptake with respect to the zero mass
  boundary condition.

Plant-N uptake constant for use with
  consumptive use values (if used).
           Starting day of run relative to time
             reference date (e.g., if reference date
             is January 15 and starting day for run
             is January 21, the relative starting
             day would be day 7).

           Termination day of run relative to time
             reference date.

           Number of soil chemistry horizons (must
             be in range 1 to 9 inclusive).

           If 1, consumptive use used to determine
             N-uptake by plants.
           If 2, reserved for future use.
           If 3, read plant N-uptake data from
             cards (see card groups 15 and 16).

           Number of temperature horizons (must be
             in range 1 to 4 inclusive).

           Number of weekly temperature data cards
             (must = 0 for NBYPAS = 1) (see group 5),

           Print interval (days) for predicted soil
             chemistry data.

           Time interval within a day on which the
             IPRINT and IMASS print options are to
             be activated.
                                  142

-------
  Column
    No.

41-45
46-50
51-55
56-60
61-65
66-70
71-75
 Var    Var
type   name

 I     INK
 I     IRERUN
 I     IPUNCH
76-80         I


Card 3 of 3

 1-5         I



 6-10         I
       IREADP
       ITEST
       START
       SM0NTH
       YEAR
        ISTOP
        IMASS
                Variable
              description

Write interval (days) for output to
  tape 2 (see section 3).

If 0, program is to be run from initial
  input deck.
If 1, program is to be restarted from
  tape or restart deck.

If 0, no restart data deck will be
  punched (a restart tape (No. 3) is
  written).
If 1, a restart data deck will be
  punched.

If 0, program is to be restarted from
  tape 3 or started from initial data.
If 1, program is to be restarted from
  cards (see group 9).

If 0, moisture flow data are read from
  tape 1.
If 1, moisture flow data are read from
  cards (see group 7).

Reference date in reference month (e.g.,
  March 21 would be STARTING DAY =21).
  See below.

Reference month.  Month to which all
  starts of the program are referenced
  (e.g., if reference month is March,
  STARTING MONTH = 3).

Year for this run (e.g., if this is
  the third year being run, YEAR = 3).
Year when run terminates  (e.g., if run
  is to terminate after 3 years and starts
  with year 3, ISTOP =5).

Print interval (days) for summary of
  nitrogen balance for system.
                                  143

-------
  Column
    No.
11-15
16-20
21-25
26-30
31-35
36-40
41-45
46-50
51-55
56-60
61-65
 Var     Var
type    name

 I      IPRINTI
 I      IPRINTJ
 I      NBYPAS
 I     SBYPAS
 I      IDYSTR
 I     IDYSTP
 I     INFIL2
 I     INFIL1
 I     ICONT1
 I     ICONT2
 I     IOP
                Variable
               description

If 1, basic control card data are
  printed.
If 0, printing of above is suppressed.

If 1, input data are printed.
If 0, printing of above is suppressed.

If 0, nitrogen transformations are
  considered.
If 1, nitrogen transformations are
  bypassed, salt reactions remain in
  model if SBYPAS = 0.

If 0, salt  reactions are considered.
If 1, salt  reactions are bypassed, nitro-
  gen transformations remain in model if
  NBYPAS =  0.

Starting day for run.  If LL > IDYSTR,
  LL - IDYSTR Records are skipped on
  tapes.

Stopping day for run (uses MM value if
  year = ISTOP).

Starting file on output tape 2 (used
  when making a restart on tape 2 con-
  taining previous files).

Starting file on input tape 1 (used
  when more than one year's data are to
  be inputed to flow calculations).
If
If -
If =
                              If
1, a new set of water application
     dates is read in each year.
     Also, no records can be skipped
     on tape 1.

1, no record skipping can occur on
     tape 2.  Otherwise (LL - IDYSTR)
     records are skipped on tape 2
     following file positioning.

1, lime precipitation is checked
     in relation to available pore
     space.
0, option is bypassed.
                                 144

-------
  Column
    No.

65-70
IOPN
                                              Variable
                                             description

                               If  =  1,  transition-state nitrification
                                         subroutine used.
                               If  =  0,  statistical nitrification
                                         equation.
                               (If = 1, constants and one statement
                                          function must be inserted
                                          into subroutine NITR; details
                                          are listed in the subroutine
                                          as comments.)
71-75
IPC02
75-80
IREK
                               If

                               If


                               If =



                               If =


ADDITIONAL DETAILS FOR CARD GROUP 2
1, user supplies pC02 valves used
     (see group 8).
0, program relates  pC02 to soil
     moisture content.

1, cation exchange  coefficients
     for Ca-Na and  Ca-Mg ion
     exchange are read from soils
     analysis data  cards.
0, default values within program
     are used.
Soil Segment  Size

Soil segment  size  (or  DELX,  see figure 1)  must be in the  range  [depth
(cm) to water table/(25  -  1)]  <_ Soil  Segment  Size <^ the size  (cm) of
the largest chemistry  or temperature  horizon.   Here the 25  refers to
array size currently used  in the program.

Converge1

This constant determines the accuracy of the  nitrogen changes computed
in subroutine TRNSFM.  A smaller value will increase accuracy and pro-
gram execution time.

Converge2

This constant determines the accuracy of mass  changes in  the system
computed in subroutine XCHANGE.   A smaller value  will increase  accuracy
and program execution  time.

Check1

This constant is used  in subroutine CHK to determine if subroutine
TRNSFM should be called  for  that time step or  bypassed and  the
                                145

-------
previously computed nitrogen changes used.  If the rates of change
for nitrogen are less than CHECK1, TRNSFM is bypassed.  However,
TRNSFM is called at least once each day to avoid possible "drift"
in the calculations.

Check2

This constant is used in subroutine CHK to determine if subroutine
XCHANGE should be called for that time step or bypassed, in which
case previously computed changes due to ion exchange, etc., are set
equal to zero.  XCHANGE is called at least once each day.

CARD GROUP 3 - Temperature Horizon Depths (Omit if NBYPAS = 1)

  Column     Var    Var                      Variable
    No.     type   name                     description

Card 1 of 1

 1-5        R     TH0R(J)      Depth (cm) from surface to bottom of
                                  first temperature horizon.

 6-10*       R     TH0R(J)      Depth (cm) from surface to bottom of
                                  second temperature horizon  (if it
                                  exists).
                                (J = subscript for each horizon.)

CARD GROUP 4 - Chemistry Horizon Depths

Card 1 of 1

 1-5        R     H0R(J)       Depth (cm) from surface to bottom of
                                  first chemistry horizon.

 6-10**      R     H0R(J)       Depth (cm) from surface to bottom of
                      (J+l)       second chemistry horizon.***
                                (J = subscript for each horizon.)
* The program allows the inclusion of up to four temperature horizons.
If included, the depths for numbers 3 and 4 would be punched in col-
umns 11-15 and 16-20, respectively.
** The program allows inclusion of up to nine chemistry horizons.  If
included, the depths for numbers 3, 4, 5, 6, 7, 8, and 9 would be
punched in columns 11-15, 16-20, 21-25, 26-30, 31-35, 36-40, 41-45,
respectively.
*** If only one chemistry horizon is desired, only one need be included.
                                  146

-------
CARD GROUP 5 - Temperature  Data (Omit if NBYPAS = 11

  Column     Var      Var                       Variable
    No-     tyP6     name                      description

Card 1 of NT*

 *~ 2                            Card indentification  (not read by
                                   program).

 3-10        R     TT(K)         Weekly temperature (°C)  for uppermost
                                   (first)  temperature horizon.

10-20**      R     TT(K)         Weekly temperature (°C)  for second
                      (K+l)         temperature horizon.***
                                 (K = subscript for weekly temperatures.)

CARD GROUP 6 - Irrigation Water Analysis

Card 1 of 1

                                 (All units  in meq/L of the species
                                   shown.)
1- 5
6-10
11-15
16-20
21-25
26-30
R
R
R
R
R
R
ANH3(1)
AN03(1)
CA(1)
ANA(l)
AMG(l)
HC03(1)
MV
N03"
Ca++
Na+
Mg++
HC03
* NT is the number of temperature  data  cards.   Each  card  contains
weekly data for all temperature  horizons.
** The program allows inclusion  of up to  four  temperature horizons.
If included, temperature data  for  horizons  3 and  4 would  be punched
in columns 21-30 and 31-40, respectively.
*** If only one temperature horizon is  desired, only one  need be
included.

Note:  The first temperature data  should  correspond  to  the week begin-
ning" with the reference data  (see  Section 5 for exceptions).
                                  147

-------
  Column     Var     Var                      Variable
    No.      type    name                     description

31-35        R     CL(1)        Cl"

36-40        R     C03(l)       C0=3

41-45        R     S04(l)       50%

Note:  All irrigation water is assumed to have same analysis.

CARD GROUP 6.5 - (Needed if SBYPAS = 1, and NBYPAS = 0)

Card 1 of Q-l

 1-5        R     SERATI0(J)   Fraction of total NHi,* which is soluble
                                  NH,/.
6-10
11-15
CARD GROUP 7
Card 1 of NS
1-10
11-20
21-30
31-40
41-50
R
R
-
*
R
R
R
R
R
U(J)
ACTCA(J)
Moisture Flow
if ITEST = 0,

CMH201 (J)
M0ISIN(J)
M0IS0UT(J)
TEN(J)
u(J)
Ionic strength - needed only when
IOPN = 1.
Ca"1"* activity - needed only when
IOPN = 1.
Data (Needed only if ITEST = 1;
tape 1 is used)

Volume of water in segment (cc) .
Water movement across upper boundary
of segment (cc/time step).**
Water movement across lower boundary
of segment (cc/time step).**
Average moisture tension (cm) over
time step (tensions shown as negative)
Plant water uptake (cm/time step/soil
segment) .
* NS is the number of moisture flow data cards.  There must be a card
for each segment including No. 1.  For details in computing NS, see
page 	.
** Positive sign for downward flow, negative for upward flow.
                                  148

-------
CARD GROUP 8 - Initial Soil  Analysis  (Omit  if IRERUN =  1)
Column
No.
Card 1 of
Var
type
NC*
Var
name

Variable
description


(Units in meq/L of species shown unless
otherwise noted.)
1- 5
6-10
11-15
16-20
21-25
26-30
31-35
36-40
41-45
46-50
51-55
56-60
61-65
66-70
71-75
76-80
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
ANH3(1)
AN03(1)
UREA(l)
CA(1)
ANA(l)
AMG(l)
HC03(1)
CL(1)
C03(l)
S04(l)
EC(1)
XX5(1)
CAL(l)
BD(1)
SAMT(l)
CNl(l)
NHi4 (soluble form) .
NO 3".
UREA.
Ca+*
Na+.
Mg*+.
HC03".
Cl".
C03=.
SO,,'.
Exchange capacity (meq/100 gm
Gypsum (meq/100 gm) soil.










soil) .

If 0.0, no lime is present in soil.
If 1.0, lime is present in soil.
Bulk density (gm/cc of soil) .
Soil organic nitrogen (ug/gm
Carbon-nitrogen ratio of soil
matter (e.g., 40:1 would be
as a 40.0).

soil) .
organic
punched
   NC is the number of chemistry horizons.
                                   149

-------
  Column     Var     Var                      Variable
    No.     type    name                     description

Card 2 of Set

 1-5        R     XTRCT(l)     Gm water/gm soil in soil extract.

 6-15        R     PC02(1)      C02 partial pressure in atmospheres
                                  (needed only if IPC02 = 1)
16-20        R     AKCS(l)      Ca-Na exchange coefficient.


21-25        R     AKCM(l)      Ca-Mg exchange coefficient.

CARD GROUP 9 - Restart Data
needed only
if IREK = 1
This data group is punched by the program during a previous run.  See
page 	 for details.  The punch/read format is (4I5/, (6E13.5/6E13.5/
6E13.5/6E13.5/E13.5)).

CARD GROUP 10 - Fertilizer Application Dates

Card 1 of 1*

 1-5        I     IT0T         Number of fertilizer applications.

 6-10        I     IADD(K)      First application day relative to ref-
                                  erence starting date.

11-15**      I     IADD(K)      Second application day relative to ref-
                       (K+l)      erence starting date.

CARD GROUP 11 - Organic Nitrogen Application Dates (Omit if NBYPAS =1)

Card 1 of 1

 1-5        I     JT0T         Number of organic nitrogen applications.

 6-10        I     I0RNAP(K)    First organic nitrogen application day
                                  relative to reference date.
* A second card may be used if needed (i.e., if the number of appli-
cations exceeds 15, in which case the 15 format still applies).
** The program allows inclusion of up to 25 fertilizer application
dates.  The same format, 15, is used for any additional dates desired.
                                  150

-------
  Column     Var     Var                      Variable
    No.     type    name                      description

H-15*       I     I0RNAP(K)    Second  organic nitrogen application day
                          (K+l)    relative  to reference date.

CARD GROUP 12 - Irrigation Water Application  Dates

Card 1 of 1**

 1-5        I     IRT0T        Number  of irrigations.

 6-10        I     IRR(K)       First irrigation day relative to ref-
                                  erence  date.

11-15***     I     IRR(K)       Second  irrigation day relative to ref-
                       (K+l)       erence  date.

CARD GROUP 13 - Fertilizer Applications

Card 1 of NF****

                                All  units in  Ibs/acre of  species shown
                                  unless  otherwise  labeled.

 1-5        R     FERT(l)      Depth  (cm)  of a uniform fertilizer
                                  application.
                                 If  = 0.0, a surface application is
                                  indicated.
 6-10         R     FERT(2)

 11-15         R     FERT(3)       N03".

 16-20         R     FERT(4)       Urea (NH2-C-NH2).
 * The program allows inclusion of up to organic nitrogen application
 dates.   If  included, application dates for applications 3,  4,  and  5
 would be punched in columns 16-20, 21-25,  and 26-30,  respectively.
 ** A second data card may be needed if more than 15 irrigation dates
 are us ed.
 *** The  program allows inclusion of up to 25 irrigation dates.  If
 included, applications 3-25 would follow the same 15 format.
 **** NF  is  the number of fertilizer applications.  The maximum number
 allowed  in  the program is 25.
                                  151

-------
  Column     Var    Var                      Variable
    No .      type   name                     description

21-25        R     FERT(5)      Ca**.
26-30        R     PERT (6)

31-35        R     FERTC7)      C03=.

CARD GROUP 14 - Organic Nitrogen Applications (Omit if NBYPAS = 1)

Card 1 of NO*

 1-5        R     0FERT(1)     Depth (cm) of uniform organic nitrogen
                                  applications (surface applications are
                                  not allowed) .

 6-10        R     0FERT(2)     Carbon: nitrogen ratio of organic matter
                                  added (containing the organic N)  (e.g.,
                                  40:1 would be punched as a 40.0).

11-15        R     0FERT(3)     Organic nitrogen added (Ibs/acre) as
                                  oven dry weight.


CARD GROUP 15 - Plant Root Distribution
Card 1 of 1
1-10
11-20
21-30
31-40
41-50
51-60

R
R
R
R
R
R

KP2(1)
KP2(2)
KP2(3)
KP2(4)
KP2(5)
KP2(6)


Fraction (decimal) of
0-1 foot depth.
Fraction
Fraction
Fraction
Fraction
Fractions
from 1 foot
from 2 feet
from 3 feet
from 4 feet
> 5 feet.


plant roots from
to 2
to 3
to 4
to 5

feet.
feet.
feet.
feet.

* NO is the number of organic matter applications.  The maximum num-
ber allowed in the program is 5.

Note:   Plant root distribution is independent of time.  If roots do
not extend to 5 feet, use zero fractions for roots below their deepest
extension.
                                  152

-------
CARD GROUP 16 - Plant Uptake  of  Nitrogen
  Column
    No.
 Var
type
 Var
name
 Variable
description
Card 1 of NP*

 1-10        X

11-20        R
       UPTK(K)
            Space for card identification.

            Plant uptake of nitrogen (lbs-N/acre/
              semimonthly).
            (K = subscript for each semimonthly
                   period.)
TAPE INPUTS
Tape input to the  Biological-Chemical  program consists  of  two optional
tapes written in binary.   Tape  1  contains  moisture  flow data written
by program INTFACE.  An alternate procedure  is to input moisture data
on cards.  In this case a  single  set of constant moisture  data  is
read.  Tape 3 may  be read  to  restart the program after  a previous run.
This tape is always written  at  the conclusion of a  run.  Unless a mag-
netic tape is equipped to  tape  unit 3, the binary data  are written on
a disk or drum.  Disk or drum data may be  lost at the conclusion of
a run.  The alternative to a  restart from  tape 3 is a restart from
data cards.
TAPE 1
             Var
            type
                                  Variable
                                 description
Logical Record

1 of NR

  1           I
       II
            Reserved for future use.
* NP is the number of  semimonthly**  plant  uptake  data  cards.  The
program requires  that  24  cards  be  present, even if not all of them
are used.
** Semimonthly means the  period from the 1st  day  through  the 15th
day or from the  16th day  through the last  day of  the month.  The
1st data card begins with the semimonthly  period  containing the
reference starting date  (see page  143).  Remaining data cards con-
tain data for consecutive semimonthly periods taken chronologically
from the 1st.
                                  153

-------
Field
No.
2
3
4
5
Var
type
I
I
I
R
Var
name
12
13
13
CMH201(J)
Reserved
Reserved
Reserved
Current
for
for
for
Variable
description
future use.
future use.
future use.
column of water
  8          R


  9          R


TAPE 3

Logical Record

1 of 1

  1          I

  2          I
                   M0ISIN(J)
                   M0IS0UT(J)
TEN(J)
U(J)
IC0UNT

INFERTIN


N0RGRIN


NTEMPIN
  Jth* soil segment .

Moisture flow (cc/time step) into the
  Jth soil segment.

Moisture flow (cc/time step) from the
  Jth soil segment.

Average current moisture tension (cm
  for Jth segment  (sign - ±) .
Consumptive use (cc/time step) for the
  Jth segment .
Restart counter for plant uptake data.

Restart counter for fertilizer applica-
  tion data.

Restart counter for organic matter appli
  cations data.

Restart counter for temperature data.
* This sequence of nine fields is repeated Q times per logical
record.  Q is the total number of segments.  Its value may be
computed using the algorithm outlined on page 155.  NR is the
number time steps for which data are written on tape 1.
                                 154

-------
Field
No.
5*
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Var
type
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
Var
name
ANH3 (J)
AN03 (J)
UREA(J)
CA(J)
ANA(J)
AMG(J)
HC03 (J)
CL(J)
C03(J)
S04(J)
EC(J)
XX5(J)
CAL(J)
BD(J)
SAMT(J)
CN1 (J)
ORN(J)
Variable
description
pg of NHij-N contained in Jth** segment
pg of NOa-N contained in Jth segment.
pg of Urea-N contained in Jth segment.
pg of Ca contained in Jth segment.
pg of Na+ contained in Jth segment.
pg of Mg++ contained in Jth segment.
pg of HC03" contained in Jth segment.
pg of Cl~ contained in Jth segment.
pg of C03~ contained in Jth segment.
«•
pg of SOit contained in Jth segment.
Exchange capacity of Jth segment.
Gypsum concentration in Jth segment
(moles/L) .
If 1.0, lime is present in Jth segment
If 0.0, lime is not present in Jth
segment .
Soil bulk density of Jth segment.
pg of organic matter just applied to
Jth segment.
C:N ratio of organic matter in Jth
segment .
pg of organic-N in Jth segment.
* Fields No. 5-33 inclusive are repeated Q times in each logical
record.  Q is the number of segments and may be determined using the
following algorithm: Q = DEPTH to W.T./DELX + 1.1, where any frac-
tion is dropped in determining the final value for Q.
** The segments begin with J = 1 and end with J = Q.
                                 155

-------
 22

 23

 24


 25


 26


 27


 28


 29


 30


 31


 32
R

R

R
R
R
R
R
R
 33

CARD OUTPUTS
RN(J)

RC(J)

E5(J)


C5(J)


SA5(J)


CAS0(J)


AGS0(J)


BNH4(J)


XTRCT(J)


ANETLIM(J)


AZE(J)





IIK(J)
Residue nitrogen in Jth segment  (pg/g).

Residue carbon in Jth segment  (pg/g).
Exchangeable Ca
  (moles/g).

Exchangeable Mg
  (moles/g).
in Jth segment


in Jth segment
Exchangeable N  in Jth segment
  (moles/g) .

Undissociated CaSOit in Jth segment
  (moles/L) .

Undissociated MgSO^ in Jth segment
  (moles/L) .
Exchangeable NH
  (moles/g) .
                                     in Jth segment
Ratio of water/ soil in the extract for
  Jth segment .

Current amount of pore space occupied by
  lime in Jth segment.

A value proportional to K1 and asso-
  ciated with lime precipitation-
  dissolution and CC>2 partial pressures.
  Value is for Jth segment.

Current lime indicator for Jth segment.
Card output from the program consists of data needed to restart a
run after a previous execution.  This card deck is generated only
if the proper control card request has been made  (see Card Group 2).
No card deck is punched if a program run terminates abnormally  (e.g.,
a fatal error occurs).  A discussion of the punch format is presented
in Section 1, under card group 9.  See tape 3, page 154, for variable
descriptions.
                                 156

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TAPE OUTPUTS
Tape output from  the  Biological -Chemical program consists of one
binary  (tape  2) and one binary (tape 3) file.  Tape 2 contains the
soil leachate data.   This may serve as input to routines which con-
sider saturated flow  and saturated chemistry.  Tape 3 contains restart
data which may be read into the program to restart a previously ter-
minated run.
TAPE 2
Logical
Record
1 of NR
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Var
type
I
I
R
R
R
R
R
R
R
R
R
R
R
R
Var
name

YEAR
IDAY
SUM0UT
DELN
AMT(l)
DEL(l)
AMT(2)
DEL(2)
AMrr(3)
DEL(3)
AMT(4)
DEL (4)
AMT(5)
DEL(5)
                                              Variable
                                             description
                               Year number.

                               Day number.

                               Water leached since start of run (cc/cm2).

                               Water leached since previous record was
                                 written  (cc/cm2).

                               N03 N leached since start of run (yg/cm2).

                               N03 N leached since previous record was
                                 written  (yg/cm2).

                               NHi/N leached since start of run (yg/cm2).

                               NH^~N leached since previous record was
                                 written  (yg/cm2).

                               Urea-N leached since start of run (yg/cm2)

                               Urea-N leached since previous record was
                                 written  (yg/cm2).

                               Ca** leached since start of run (yg/cm2).

                               Ca*"1" leached since previous record was
                                 written  (yg/cm2).

                               Na* leached since start of run (yg/cm2).

                               Na* leached since previous record was
                                 written  (yg/cm2).
                                   157

-------
Logical
Record
15
16
17
18
19
20
21
22
23
24
Var
type
R
R
R
R
R
R
R
R
R
R
Var
name
AMI (6)
DEL(6)
AMI (7)
DEL (7)
AMT(8)
DEL(8)
AMI (9)
DEL (9)
AMT(IO)
DEL(IO)
Variable
description
Mg leached since start of run (yg/cm2) .
Mg leached since previous record was
written (yg/cm2) .
HCO~3 leached since start of run (yg/cm2)
HCO 3 leached since previous record was
written (pg/cm2) .
Cl~ leached since start of run (yg/cm2).
Cl~ leached since previous record was
written (pg/cm2) .
C0~3 leached since start of run (pg/cm2).
C0~3 leached since previous record was
written (yg/cm2).
SO", leached since start of run (yg/cm2) .
S0~. leached since previous record was
                                written (yg/cm2).

NR is the number of records written on tape 2.  The write interval
(i.e., time between write operations is specified by the user (see
card group 2)).

HINTS ON PROGRAM USE

   a.  Be sure core is set to zero before program is loaded.

   b.  The program can be operated very easily from a time-share ter-
   minal.  This should be done when possible.

   c.  Subroutines will not load in a random order due to varying sizes
   of common blocks.  See suggested load sequence on page 160.

   d.  An end-of-file is written on tape 2 at the conclusion of a run
   and at the end of each year.  This means that output from several
   runs and/or years may be stored as separate files on the same or
   individual tapes.
                                  158

-------
e.  A run which exits due to  a  time  limit  or  other error will not
produce a restart deck or tape.

f.  The number of temperature cards  may  be reduced when making a
restart run by altering the value  of the number contained in
Field No. 4 of the restart deck or tape.   The number placed there
by the program is the number  of cards or records  to skip in order
to locate the correct temperature  data card.

g.  If no plant uptake of N is  required, set  CROP equal to 1 and
leave columns 51-55  of the first control card blank.   In this
case, CARD GROUP 16  may be omitted from  the deck.

h.  When using the IOPN = 1 option,  values for certain parameters,
plus a statement function must  be  inserted into NITR.

i.  The program can  be operated with either the salt portion or the
nitrogen portion bypassed.

j .  The program can  be operated so that  certain months of the year
are bypassed.

k.  Be sure to check the input  data  carefully.  The program may run
and terminate normally with bad data.

1.  The mass balance check on nitrogen is  an  important item.  Any
large errors here indicate something has gone wrong.

m.  If a run should  "blow up" first  check  your card input data and
then any data being  read from tapes.

n.  An average execution time on a CDC CYBER  74-28 is  about 0.4
second/day using  11  segments  and 0.1 day time steps.
                                 159

-------
SUGGESTED LOAD SEQUENCE




                     Load order
Routine
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
MAIN
COMBINE
TRNSFM
XCHANGE
EQEXCH
NITR
NEGN
SALTBP
EXECUTE
MCHECK
OUTPT
DAY
I DAY
THEDATE
UNITS 1
FL
PRNT
WGT
UPTAKE
CHK
TEMP
QROTP
QTRAN
COMP
PHCALC
SKIP
                                 160

-------
                          SECTION  XIV

                         USER'S MANUAL

                     SATURATED FLOW PROGRAM

INTRODUCTION

This program was designed to predict the  average or steady-state
response of a subsurface drainage  system  to  deep percolation inputs.
The drainage system consists of parallel,  equally spaced, tile drains.
Either the average annual deep percolation rate for uniform seepage
(boundary condition 1,  BC1) or the average annual water table position
for the ponded water case  (boundary condition  2, BC2) provide the
flow inputs.  In particular, this  program was  developed as part
of an irrigation return flow water quality model.

For computation purposes, the saturated aquifer is divided into a
number of individual stream tubes.   Discharge  rates through each
tube are identical.  In addition,  a node  concept is employed to
permit the determination of each tube's location.  Theoretical
techniques and details  are contained in the  program description.

Output includes the position of the water table (BC2) or the seepage
distribution between drains (BC1),  location  of the stream tubes, time
of travel down each tube, pore volume of  each  tube, and the steady-
state discharge from the drains.   Pore volumes are intended for input
to the saturated chemistry portion of the water quality model while
the drain discharge and travel times are  input to the drain effluent
prediction portion.

UNIT NUMBERS

Two input-output devices are referenced by the program:

      Unit                       Unit description
  designation                        or purpose

       5        The common input tape or  unit  (CIT).  It is the  ,
                computer system's  standard input device.

       6        The common output  tape or unit (C0T).  It is the
                computer system's  standard output device.

In addition, the program uses an internal  scratch or peripheral
storage unit (unit 8) which is assigned to disk.  Data defining the
streamline locations are written without  format (binary) if a cathode
                                  161

-------
ray tube (CRT) plot of the streamlines using a distorted vertical
scale is requested.

DATA DECK STRUCTURE

Seven input cards are required for BC1 and eight for BC2 as shown
in Figure 22.  Certain cards are common to both boundary conditions.
Referring to the card numbers of Figure 22, the input deck for BC1
consists of cards 1, 2, 3, 4A, 5A, 7, and 8 while for BC2 cards 1,
2, 3, 4, 5, 6, 7, and 8 are used.
CARD GROUP 1 - Title Information
Column
No.
Card 1 of 1
1-80
Var
type

A
Var
name

TITLE j
                                               Variable
                                             description
                                An 80-character alphanumeric title
                                  used to identify all printed and
                                  plotted output.  If this title is
                                  desired to be centered on output,
                                  it must be centered on the card.
CARD GROUP 2 - Problem Selection
Card 1 of 1

 1-40          I
(4011 Format)
IPR0B(I)     A control array which calls the proper
              overlay for execution.  Individual
              programs in the water quality model
              were originally designed for inclusion
              in an overlay system.  Presently
              (March, 1973), only the saturated flow
              and drain effluent portions are
              included.  When IPR0B(I) is set to 1,
              the Ith overlay is called.  Thus

               IPR0B(1) = 1, call the saturated
                               flow routine.
               IPR0B(2) = 1, call the drain efflu-
                               ent routine.

            On output, values of IRP0B(I) are
              listed as I0C values under the
              heading - PROBLEM CONTROL INFORMATION
              FOR MAIN PROGRAM.
                                  162

-------
                                                      No. of stream
                                                       tubes
/Grid division
- 1
/Geometry
t
\
. 	 	 - 	 .- , -A— 	 	 	

^~~
	 (4 A
^ 	 -•
                  \
           Boundary input/output
            options
       Problem selection
/TitU
                                                 Porous media
                                                  properties
   FIGURE  22.  DATA DECK  STRUCTURE-SATURATED FLOW SUBMODEL
                                   163

-------
  Column
    No.
 Var
type
 Var
name
               Variable
             description
CARD GROUP 5 - Boundary Condition and Input/Output Options

Card 1 of 1
 1-10
       IBC
11-50
(4011 Format)
            Boundary condition selector.

               IBC = 1, selects the ponded water
                          case.
               IBC = 2, selects the uniform seepage
                          case.
               IBC = any other value will produce
                       questionable results.
                       (There is no check for a
                       legitimate boundary con-
                       dition number.)
               The boundary condition number is
                 incorporated into a subtitle on
                 output.

            I0C(I) = An input/output option array
                       used to select printed and
                       plotted output.   (See
                       Input/Output Options.)
CARD GROUP4 - Geometryfor BC2 (see Figure 25)

Card 1 of 2
 1-10
  R
DG
11-20
21-30
Card 2 of 2
1-10
R
R

R
A
ER

DG
11-20
       AG
Distance from horizontal centerline
  of drain to the impermeable barrier
  (feet).

Drain spacing (feet).

Effective drain radius  (feet).

Geometry for BC1 (see Figure  23).

Distance from horizontal centerline
  of drain to the impermeable barrier
  (feet).

Drain spacing (feet).
                                 164

-------
             -Water table
              • Perm • / .'
              .  pore
o
                            o •  .
             -  • .  •  •  "-.-•..'• 17 .
      -Impermeable barrier .' '. •   • •   • y

          wr^//&ff^//j^^^^^ff^f^//^
                AG
      (a)  BOUNDARY CONDITION  1
        Uniform  seepage
       • ^ Impermeable barrier • .o
               cO "  ' . " '  ' 4 •  . ' ,
                                       Seep
     (b) BOUNDARY  CONDITION 2

FIGURE 23.  BOUNDARY  CONDITIONS-
     SATURATED  FLOW SUBMODEL
                   165

-------
  Column      Var    Var                       Variable
    No.       type   name                     description

21-30          R    H           Vertical distance from the water table
                                  to the horizontal centerline of the
                                  drain (feet).

31-40          R    ER          Effective drain radius (feet).

CARD GROUP 5 - Grid Division Data for BC2

Card 1 of 2

 1-5          I    Ml          The number of primary grids to be
                                  subdivided in the horizontal
                                  direction.

 6-10          I    Nl          The number of primary grids to be
                                  subdivided in the vertical
                                  direction.

11-15          I    L           The number of subdivisions of the
                                  primary grid.

16-25          R    HG          The nominal size of the primary grid
                                  (feet).

Card 2 of 2                     Grid division data for BC1.

See above           Ml          Same description as in card 5.
                    Nl
                    L

CARD GROUP 6 - Seepage Rate for BC2

Card 1 of 1

 1-10          R    SEEP        Average annual seepage or deep per-
                                  colation rate between the drains
                                  (feet3/feet2/year or feet/year).

CARD GROUP 7 - Porous Media Properties

Card 1 of 1

 1-10          R    PERM        Coefficient of permeability (feet/year)
                                 166

-------
  Column
    No.
11-20
 Var
type


  R
 Var
name^


P0RE
  Variable
description
                                 Total  porosity  expressed  as a decimal
                                   (feet3/feet3  or dimensionless).
CARD GROUP  8 - Number  of  Stream  Tubes
Card 1 of  1
 1-10
STANDARD OUTPUT
       NST
            The number of stream tubes or stream-
              lines used to define flow from one
              side of the drain.
Output includes results  printed  on  unit  6  and plotted on a cathode
ray tube  (CRT) plotter*.  Certain portions  of the printed output
are standard while others are  optional.  All CRT plots are optional.
The next  section describes  the optional  output.

Standard  printed output  common to both boundary conditions includes:

   a.  input/output options (I0C(I));

   b.  boundary condition number;

   c.  given and modified aquifer geometry;

   d.  porous media properties;

   e.  grid division data;

   f.  number of stream  tubes;

   g.  flow into the drain  per foot of length;

   h.  travel time down  each tube;

   i.  pore volume contained in  each tube;

   j.  error messages, if any.

In addition, standard output for BC1 includes the average seepage
rates between adjacent streamlines as well as the average rate
between drains.  For BC2, additional output includes the ratio of
the seepage rate to the permeability and the maximum and minimum
water table position at 50, equally spaced points between the drain
and the midpoint between drains.
* Plotter subroutines are not included in the model version included
in this Volume.
                                 167

-------
INPUT/OUTPUT OPTIONS

Individual output options are selected by setting the appropriate
I0C(I) value to 1.  Options are bypassed if the value is left blank
or set to 0.  Available options are identical for both boundary condi-
tions with the exception of I0C(28) which only applies to BC1.  The
descriptions below may be more meaningful if reference is made to
the computational approach described in the program description.  It
should be noted that most of the print options are intended for
debugging use.

I_       Option

1       Select all print options.  All individual print options
        (1=3 through 25) are set to 1 by this option.

2       Select all CRT plot options.*  All individual plot options
        (1=26 through 40) are set to 1 by this option.

3-25    Reserved for individual print options.

3       Print required values of streamlines used to define the
        flow system.

4       Print coordinates of all nodes.

5       Print coordinates and the stream function at all nodes
        that are required to define the system.

6       Print coordinates and corresponding potentials for all
        points locating the required streamlines after horizontal
        interpolation.

7       Print coordinates and corresponding stream function for
        all nodes in each vertical column of nodes.

8       Print coordinates and corresponding potentials for all
        points locating the required streamlines after horizontal
        and vertical interpolation.

9       Print coordinates and corresponding potentials for all
        points defining a streamline before sorting  (raw data).

10      Print coordinates and corresponding potentials for all
        points defining a streamline after sorting (sorted data).
* Not available in this version of the model.
                                  168

-------
I       Option

11      Print coordinates  and corresponding potentials  for all
        points defining  a  streamline after the sorted data have
        been modified  to exclude points within the drain and  a
        point added  on the drain perimeter (modified data).

12-25   Options  are  not  presently used (March, 1973).

26-40   Reserved for individual  plot options (not available).

GRID DIVISION AND GEOMETRY MODIFICATION

Application of the node  concept  based on input of grid  division data
has been  explained in  the  program description.  Given (input) dimen-
sions of  the aquifer are automatically adjusted by the  program so
that the  aquifer geometry  is  a multiple of the primary  or coarse grid
size.

For BC1,  the depth from  the water table to the horizontal centerline
of the drain, H, is  used for  the coarse grid size.   Both the  depth
to barrier, DG,  and  drain  spacing,  AG, are modified.  Since the user
has no control over  the  coarse grid size,  the effect  of geometry
adjustments is of interest.  The computed  drain discharge is  a prime
indicator of this effect.   Figure 24 presents the effect on the
dimensionless flow parameter  of  various dimensionless geometry
parameters:

   a.  Ratio of  drain  depth to barrier depth.

   b.  Ratio of  drain  spacing to drain depth.

   c.  Ratio of  effective  drain  radius to  drain depth.

For normal drainage  situations,  the solution is seen  to be relatively
insensitive to changes in  the aquifer geometry.

For BC2,  the nominal size  of  the primary grid, HG,  is input.  Because
drain discharge  is directly proportional to the drain spacing, A,
HG is adjusted so A  is a multiple of the adjusted size.   The barrier
depth, DG, is then modified.   If HG is judiciously chosen, or if it
is made small relative to  DG, adjustments  can be minimized.

LIMITATIONS AND  ERROR  MESSAGES

The program description  lists limitations  on the size of the problem
that can  be analyzed.  They are  repeated here:
                                 169

-------
o
4.U
3.8
3.6
3.4
3.2
3.0
2.8
2.6
2.4
2.2
2.0
IB
1.6
1.4
1.2
i.O
^80, It

No




^40
V-20 :
Mo


x40-8
^-20

/4Q,e
^20



>0






,80,160
f===a.



3O,I60
- —
V|Q


^v.
^
_r
c



=====
r
d

=====
r
d

X
- - 0.40



W
"*-N
- = 0.20

=^— H
-=0.10
0,l60-[4- parameter
KIQ



T— -
_r
c


: = 0.05




\




\


"~^
- — ~^






V



X


^

'^-^,


water tabie-^

o '

Q=fl
.p
Denote
is 90
.deep
\


\


\
^


- . '• ' • -o
,,o • . •
Q
ow intc
er unit
s locat
% of th
aquifer
\
^/Cutc
t/ the
the

[£a_

) one drain
drain length
on (-§•) at whic
at for an infir


^ Kd
n'teiy
)ff limits based on
drain just touching
impermeable barrier
¥ °r |=%
*wwsnwMw*''W* A i
or f = (
\
\
x
^



\
ro
ro
- oo
\
\





en
o
V
\ [^
(Ti
D O.I 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
d/D
i \
l*r/d '
.0
         FIGURE  24. DIMENSiONLESS  FLOW
CIRCULAR TILE DRAINS BELOW HORIZONTAL WATER TABLE
                        170

-------
   a.   Maximum total number of nodes is 3,000 and the maximum number
   in  any vertical grid line is 400.  Since these numbers depend on
   the aquifer geometry and grid subdivision data, the user has
   direct control.  Equations to check these numbers prior to a
   run are given in the next section.

   b.   Maximum number of interpolated points defining the streamlines
   is  3,000.  The user has indirect control on this number since it
   depends on the number of nodes and streamlines, as well as the
   aquifer geometry and boundary conditions.  If this situation is
   encountered, a coarser grid can be used or the number of stream-
   lines reduced.

   c.   Maximum number of stream tubes is 20.  If more are specified,
   the program notes the condition, reduces the number to 20, and
   continues.  It should be noted that other programs in the water
   quality model can only accept information for 10 tubes (i.e.,
   SATCHEM and DEO200) .

   d.   Maximum seepage rate for BC2 must be less than the permeability.
   This restriction is imposed by the physical nature of the problem
   since the ultimate steady state would be the ponded water case.

Error messages are generated if the above limitations are violated.
In addition, failure of the infinite series for the solution constants,
stream functions, and potential functions produce error messages.  A
list of all error messages is contained in the Appendix.  Suggested
courses of action when errors do occur are included.

EQUATIONS FOR NUMBER OF NODES

If the user has specified subdivision information which causes more
than 3,000 nodes to be computed, an error message is generated and
execution is terminated.  Should there be any suspicion that this
situation might prevail, the equations given below may be used to
avoid possibly unproductive runs.

For BC1, the equation is

               NT  =  MP+(MP)(NP)+NP+(MH-N1)(L-1)                  [50]
                      + (M1)(N1)(L2-1)+3L(2L+1)

   where NT is the total number of nodes  (excludes origin);
         MP is the number of primary grid elements in the
           horizontal direction;
         NP is the number of primary grid elements in the
           vertical direction; and
         Ml, Nl, L are as described in the Data Deck section.
                                 171

-------
For BC2, the equation is

               NT  =  MP+(MP)(NP)+NP+(M1+N1)(L-1)                  [51]
                      + (Ml)(Nl)(L2-l)+L.(3L+2)

   where all terms are defined as before.

The determination of MP and NP requires use of the methods employed
by the program in modifying the aquifer geometry.  For BC1, the
following procedure is followed:

   a.  Compute DG/H and AG/(2H).

   b.  Then NP is the integer part of DG/H if the decimal part is <0.5.
   MP is the integer part of DG/H increased by 1 if the decimal part is
   >0.5.

   c.  Similarly MP is the integer part of AG/(2H) is the decimal part
   is <0.5.
   MP is the integer part of AG/(2H) increased by 1 if the decimal
   part is >0.5.

As an example, if DG = 28., AG = 150., and H = 10., then DG/H = 2.8,
AG/(2H) =7.5 from which NP = 3 and MP = 7.

For BC2, the following procedure is used:

   a.  Compute A/(2HG).

   b.  Then MP is the integer part of A/(2HG) if the decimal part is
   <0.5.
   MP is the integer part of A/(2HG) increased by 1 if the decimal
   part is >0.5.

   c.  The modified primary grid size is H = A/(2MP).

   d.  Compute DG/H.

   e.  Then NP is the integer part of DG/H if the decimal part is
   <0.5.
   NP is the integer part of DG/H increased by 1 if the decimal
   part is >0.5.

As an example, if DG = 28., A = 150., and HG = 10., then A/(2HG) = 7.5,
MP = 7, and H - 150/14 - 10.71.  Computing DG/H = 2.6, NP = 3.
                                 172

-------
An additional restraint on program use is the limitation that the
maximum number  of nodes on a vertical grid line must not exceed 400.
The following equations may be used to compute this number:

                 BC1   NC = CNP+1) + Nl(L-l) + 2L                  f52l
                 BC2   NC = (NP+1) + Nl(L-l) + L                   [53]

LOGICAL ERROR MESSAGES

The following error messages may be generated during execution.   The
boundary condition to which a particular error message applies  is
indicated by the BC column.  If the same message applies to both
boundary conditions, both numbers are shown.

No.   BC_      Message

 1     1      Computation of the stream function by subroutine  SF0113
              was attempted for a point outside the aquifer boundaries.

 1     2      Computation of the stream function by subroutine  SF0101
              was attempted for a point outside the aquifer boundaries.

 2     1      Computation of the stream function by subroutine  SF0113
              was attempted for the origin.

 2     2      Computation of the stream function by subroutine  SF0101
              was attempted for the origin.

 3     1      The series for the stream function did not converge
              according to the tests applied  in subroutine  SF0113.
              The maximum limit of 30 terms was reached.

 3     2      The series for the stream function did not converge
              according to the tests applied  in subroutine  SF0101.
              The maximum limit of 999 terms  was reached.

 4    1,2     The number of nodes computed by subroutine SF0111  exceeds
              the dimensioned storage of 3,000.

 5     1      The series for the constant lower case Q did  not  con-
              verge according to the tests applied in subroutine
              SF0114.   The maximum limit of 30 terms was reached.

 5     2      The series for the constant C did not converge according
              to the tests applied in subroutine SF0102. The maximum
              limit of 999 terms was reached.
                                  173

-------
No.   BC      Message

 6     1      The series for the potential function did not converge
              according to the tests applied in subroutine SF0115.
              The maximum limit of 30 terms was reached.

 6     2      The series for the potential function did not converge
              according to the tests applied in subroutine SF0103.
              The maximum limit of 999 terms was reached.

 7    1,2     The number of points in a vertical column exceeds the
              dimensioned storage of 400.

 8    1,2     The number of interpolated points exceeds the dimen-
              sioned storage of 3,000.

 9     2      The number of points locating the streamlines exceeds
              the dimensioned storage of 3,000 after adding points at
              the water table.

10    1,2     The number of points defining a streamline exceeds the
              dimensioned storage of 3,000.

11     1      The series for the potential function did not converge
              according to the tests applied in subroutine SF0115.
              The maximum limit of 30 terms was reached.  The sub-
              routine to compute the potential function was called
              by SF0120.

11     2      The series for the potential function did not converge
              according to the tests applied in subroutine SF0103.
              The maximum limit of 999 terms was reached.  The sub-
              routine to compute the potential function was called
              by SF0120.

12    1,2     The number of points defining a streamline exceeds the
              dimensioned storage of 3,000 after subroutine SF0120.

13     2      The series for the potential function did not converge
              according to the tests applied in subroutine SF0103.
              The maximum limit of 999 terms was reached.  Subroutine
              SF0103 was called by SF0122.

14     2      The ratio of the seepage rate to the permeability is
              equal to or greater than 1.00.  There is no steady-
              state solution under these conditions.  The case of
              uniform seepage must eventually yield the ponded
              water case.
                                  174

-------
No.   BC      Message

15    !»2     The number of required streamlines exceeds the dimen-
              sioned storage of 20.   This number is being reduced to
              20 by the  program.

Messages 1, 2,  and 15  are not fatal.  The remaining messages are
considered fatal and execution is terminated.   If any of these error
messages are encountered, the following tabulation suggests means to
correct the deficiencies.

No.           Course of  Action

1>2           These are  nonfatal  and are primarily debugging messages.
              Unless program changes are made,  the user should never
              encounter  them.

3,5,6,11,13   These fatal errors  all involve failure of the various
              infinite series to  converge.  Details of the tests are
              contained  in the program description.  Two alternatives
              exist:

                 a.  Increase the maximum number of terms in the
                 given subroutine.  It is set  at the start of the
                 subroutine by the arithmetic  statement MMAX = 30
                 or MMAX = 999.   Run times will increase.

                 b.  Increase the test value for the ratio test
                 in the  given subroutine.  It  is set at the start
                 of the  subroutine by the arithmetic statement
                 RATI0 = .000001.  Both run times and solution
                 accuracy will decrease.

              The appropriate subroutines are  included in the messages
              and are  summarized  as:

                 BC      Stream    Solution  Potential   No.  of
                 No.   function   constant  function^    terms

                                                             30
                                                            999

              Messages 3, 5,  6 are generated in computing values for
              nodes or interpolated  points. Subroutine SF0120 in
              message  11 modifies points within the drain and adds
              one on the perimeter.   Subroutine SF0122 in message 13
              computes water table locations for BC2.
1
2
SF0113
SF0101
SF0114
SF0102
SF0115
SF0103
                                 175

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No.           Course of Action

4,7           These fatal errors involve the aquifer geometry and grid
              information.  A redefinition of the grid using a coarser
              net is required.  The equations in the main part of this
              manual can be used as guides.  (See Equations for
              Number of Nodes.)

8,9,10,12     These fatal errors involve both the grid data and the
              number of streamlines.  Either the grid should be made
              coarser or the number of streamlines reduced.  Mes-
              sage 8 is generated during interpolation for all stream-
              lines before adjustments at the drain or water table are
              made.  Messages 9, 10, and 12 apply to a single stream-
              line.  Message 8 will normally be encountered before any
              of the others unless only 1 stream tube is used.  Mes-
              sage 9 is generated for BC2 when points are added to the
              water table.  Message 12 results when points are deleted
              and added at the drain.

14            This fatal error involves use of the wrong boundary
              condition based on the ultimate steady state.  For
              normal drainage applications, this situation indicates
              severe waterlogging problems.

15            If more than 20 streamlines are desired, program
              dimensions for V0L(I), XST(I), and TRAVEL(I) must be
              increased.  In addition, the error message generator
              in subroutine SF0112 must be changed.
                                 176

-------
                            SECTION XV

                          USER'S MANUAL

                   SATURATED CHEMISTRY PROGRAM

INTRODUCTION

The Saturated Chemistry Program was originally designed as  part  of
the irrigation return flow quality model.   Dutt and Shaffer(4) have
presented the basic theory and concepts used.  The program  has been
expanded to allow  its use in return flow studies not utilizing the
Unsaturated Flow and Chemistry Programs.  Also, provision has been
included for salt  movement across the barrier (lower boundary),  and
user inputed values for ion exchange coefficients and CO partial
pressures.                                               2

The two-dimensional saturated system drained by parallel rows of
circular drains is divided into a number of stream tubes.   Discharge
through each tube  is identical although the soil mass is not.  Indi-
vidual tubes may also be subdivided into a number of elements, each
having the same soil mass.   As shown in Figure 25,  these elements are
in series with respect to the path of flow.

The system is defined by specifying the number of tubes  and for  each
tube the total pore or water volume, average volumetric  moisture con-
tent, stream tube  width at the water table,  and the number  of sub-
divisions.  Each tube can be initially treated as chemically homo-
geneous or each element can have a unique  soils analysis.   Once  the
system is operating, an initially homogeneous system will soon become
heterogeneous due  to different soil volumes in each tube, chemical
reactions, and piston displacement effects of the deep percolation
water.  When a restart deck is punched at  the end of a run, current
soils data for every element in every tube reflect  the heterogeneous
condition.

Inputs to the saturated system include the amounts  and quality of
deep percolation water.   This may be taped output from the  unsaturated
chemistry portion  of the return flow model or may be input  by cards.
When cards are used, inputs may represent  output from the unsaturated
zone (either observed,  predicted,  or guessed data)  or surface inputs.
Surface inputs, in turn,  would logically be used when the unsaturated
zone is nonexistent (for example,  the ponded water case), when the
zone is bypassed because changes within it are minor in  comparison to
those in the saturated system, or when the program is being used to
simulate the unsaturated zone.   In this case, input data could be the
estimated deep percolation  and the corresponding quality of the  applied
                                   177

-------
                                         Water  table
                                                          Mid- point flow  line
                                                                    /Tube  I
Tile drain
                                                                      Segment or
                                                                      element no.
                             In general, max.(I).
         FIGURE  25.  SEGMENTED FLOW TUBE IN SATURATED REGION.
                 EXAMPLE OF  10 SUBDIVISIONS. (MAX (I) = 10)

-------
water or water of surface quality can be entered along with the onfarm
irrigation efficiency.   In the later case, the program removes the
consumptive use  from the input water and concentrates it accordingly.

Output from the  program includes printed results showing the quality
of water discharging from each tube, punched restart chemistry decks,
and taped quality output.  The taped output is intended for input to
the drain effluent prediction portion (program DE0200) of the water
quality model.

UNIT NUMBERS

Card input is accomplished by READ statements without a unit number
and listed output by means of PRINT statements.  The common input
(CIT) and output (C0T)  devices are understood to be used.  Punched
output  (restart  deck) is accomplished by PUNCH commands.  In addition,
the program references  additional units:

   Unit                             Unit description
designation                            or purpose

    15         The unit on which the file containing deep percolation
               quantities and qualities is mounted.  This file is
               written  by the unsaturated chemistry portion of the
               water quality model.  When these data are input by
               cards, they are transferred to unit 15 and the program
               functions as if a saved tape existed.  (See Tape Input.)

    16         The unit on which the file containing the quality of
               water discharging from each tube of the saturated system
               is mounted.  This file is intended for input to the
               drain effluent prediction portion of the quality model.
                (See Tape Output.)

    17         An internal scratch unit on which the last year's data
               are written.  This allows repeated reading of these data
               as a single file.

    18         Output data written to this file in format suitable for
               a read in a subsequent run as unit 15 (IWR must = 1).

    20         This file contains 7 coded output giving the total num-
               ber of slugs generated for each stream tube during the
               run.  Information is used as partial input to the drain
               effluent prediction submodel.
                                  179

-------
DATA DECK STRUCTURE

There are six groups of input cards from which the data deck  for a
given run is composed, as shown in Figure 26.  The format  for each
group, except group 6 (restart deck), is illustrated in Figure 26.
Variables are defined below.  Note that the card numbers refer to
card types and not the actual number of a given type.
CARD GROUP 1 - Title Card
Column
No.
Var
type
Var
name
Card 1 of 1
 1-80
     TITLE
CARD GROUP 2 - Control Card
Card 1 of 2
 1- 5
I    ICARD
 6-10
11-15
I    INFIL15
I    LSFIL15
16-20
I    NREPT
21-25
I    INFIL16
                                               Variable
                                             description
An 80-character alphanumeric title used
  to identify the printed output.
Flag to indicate the input medium for
  the deep percolation inputs.
If ICARD = 1, then read input from
                cards (group 5) .
If ICARD $ 1, then read input from
                magnetic tape (unit  15).

The initial file number to be read on
  unit 15.  (See Tape Input.)

The last file number to be read on
  unit 15.  When deep percolation data
  are read from cards (ICARD =  1),
  LSFIL15 is the number of years of  data.
  (See Tape Input.)

The number of times the last file on
  unit 15 (LSFIL15) is to be repeated as
  input.  This option is available for
  both tape and card input.   (See Tape
  Input.)

The number of the initial file  to be
  written on unit 16.   (See Tape Output.)
                                 180

-------
            NANAL=0
                 r
                                      ONE YEARS DATA, REPEAT
                                        FOR SUCCESSIVE YEARS
                        y Restart deck
                                              Soils analysis
GROUP 5 DETAILS
      \
                             IRERUN = I
                                  /lubedata
Salt from
barrier data
    /Deep perc.
        data
           \
           \
                                                    MRERUN^I
             FIGURE  26.  DATA DECK STRUCTURE
             SATURATED  CHEMISTRY  SUBMODEL
                               181

-------
  Column
    No.

26-30
31-35
36-40
41-45

46-50
I

R
                           Variable
                         description

ISAME       A flag to denote whether  each  tube  is
              assumed homogeneous with respect  to
              soil chemistry or if each segment in
              the tubes has a different analysis.
            If ISAME = 1, then each tube is homo-
                            geneous and there will
                            be one group 4 card
                            for each  tube  (MAXTU
                            cards).
            If ISAME j* 1, then there  will  be a
                            group 4 card for each
                            element in a tube (MAX(I)
                            cards for tube I).   (See
                            group 3 cards  below.)

IRERUN      Flag to denote a restart  run.
            If IRERUN = 1, then this  is a  restart
                             run.  A  restart deck
                             (group 6) is  used  and
                             initial  soils analyses
                             are deleted (group 4).
            If IRERUN t 1, then this  is an initial
                             run and  soils data are
                             inputed  (group 4).

IPUNCH      Flag to signal punching of a restart
              deck.
            If IPUNCH = 1, punch a deck at the  end
                             of the run.
            If IPUNCH •£ 1, then do not punch.

MAXTU       Number of stream tubes used.

CHI         Convergence criterion for the  ion
              exchange routine.  It is the number
              of moles/liter which is considered
              as insignificant.  Suggested values
              range from 10~2 to 10~6 with a recom-
              mended value of 10"1*. .
                                 182

-------
  Column
    No.

51-55
56-60
61-65
66-70
71-75
76-80
 Var    Var
type   name

  I    IDUMP
       IINJE
       SBYPAS
       IREK
       IDN
       IPC02
               Variable
             description

If = 1, the chemical composition of the
          water contained in each tube
          element is printed at the end
          of the run and represents the
          chemical status at this point
          in time.
If = 0, this output is suppressed.

If = 1, the salt injection option is
          activated.  (Group 3 must be
          present.)  See Figure 27 for
          details.
If = 0, option is bypassed (group 3
          must be absent).

If = 1, the chemical reactions (salt)
          within the program are
          bypassed.
If = 0, the chemical reactions are
          included.

If = 1, cation exchange coefficients
          for Ca-Na and Ca-Mg ion
          exchange are read from the
          soils analyses data cards.
If = 0, default values within the model
          are used.

If = 1, the denitrification subroutine
          is utilized.
If = 0, denitrification subroutine is
          bypassed.

If = 1, user supplied pC02 values used1
          (see group 6).
If = 0, program relate:   pC02 to soil
          moisture content.
Card 2 of 2

 1- 5
       IWR
If = 1, output written to file Tape 18
          in binary format suitable for
          a subsequent read as file
          Tape 15.
If = 0, no write to file Tape 18.
                                  183,

-------
Mass f lux,
                 *  *
                  *  *
  «  «   X  X   * X
X           "
 x  x  x  x „   x  *
       X   XX    X
                       * * x  x"  „* « x
                                         * *
                          Water of aqu i fer
                            qual i ty (Iower
                            tube)

                          Transition zone(AX)
                            Barr i er
                                              yater  of  Barrier
                                                qual ity  (constant
                                                with  t ime)
Mass Fluxj


Mass Flux;
                    D
                    D.
-££1
 rf-X
                 Bas i c equat i on


                 Approximate equation
                   (steady state)
                   (for any t ime step)
Where:   Ci  is the concentration of constituent i.

        D is  a mean  diffusion coefficient.
     FIGURE  27.   SALT INJECTION FROM  THE  BARRIER

-------
CARD GROUP  3  -  Deep Percolation Data
This group  is  only used when ICARD = 1.  It includes the three types
of cards described below.  Cards must be placed in chronological order
with each year's  data preceded by a type 1 card.  This card is fol-
lowed by the appropriate combination of card types 2 and 3 as indicated
in Figure 26.  •(See NANAL below.)  Checks are not made on the chrono-
logical order  and it is possible to include more than one application
on a single day by using separate type 2 cards.  The total number of
years of data  is  LSFIL15.  (See Tape Input.)
  Column
     No.

Card 1  of 3

  1-  5
 Card 2 of 3

  1- 5
  6-10
 11-15
 Var
type
 Var
name
       NIRR
       IM0N,
          IDAY,
          IYEAR
 16-25
  R
APP
 26-30
       NANAL
               Variable
             description
Number of water applications or deep
  percolation inputs for the current
  year.

Deep percolation volumes.

The month, date, and year on which the
  deep percolation occurred.  For exam-
  ple, July 17, 1973, would be IM0N = 7,
  IDAY = 17, IYEAR = 1973.  The month
  and day are converted to the Julian
  day, which along with the year, is
  written on unit 15 for information
  purposes.

Amount of deep percolation for this
  application  (inches3/inch2 or inches).
  A + value is an input to the saturated
  system, while a - value denotes flow
  from the saturated to unsaturated
  system.

Flag used to denote the need for a new
  water quality analysis.
If NANAL = 0,  the previously read
                analysis is to be used
                with this application.
If NANAL t 0,  a new analysis is  to be
                read and a  type  3 card
                will immediately fol-
                low this  type  2  card.
                                   185

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Column
No.
31-46


47-56

Card 3 of 3

1- 5
6-10
11-15
16-20
21-25
26-30

31-35
36-40
41-45
CARD GROUP 4
Card 1 of 2
1-10
Var
A


R



R
R
R
R
R
R

R
R
R
- Data

R
Var
name
S0URCE


E



ANH4
AN03
CA
AMG
ANA
HC03

C03
CL
S04
for Salt

DIFK
Variable
description
A 16-character alphanumeric name which
can be used to identify the source of
the deep percolation water. For exam
pie, PR0JECT WATER or PRECIPITATI0N
or SN0WMELT. It is printed on output
for information purposes only.
Onfarm irrigation efficiency (percent
basis) .
Quality analysis of deep percolation
water.
Ammonium (NH^*) concentration (meq/1).
Nitrate (N03~) Concentration (meq/1) .
Calcium (Ca++) concentration (meq/1) .
Magnesium (Mg*+) concentration (meq/1) .
Sodium (Na+) concentration (meq/1) .
Bicarbonate (HCOs") concentration
(meq/1).
Carbonate (C03=) concentration (meq/1) .
Chloride (Cl~) concentration (meq/1).
Sulfate (50^=) concentration (meq/1) .
Movement (Injection) From Barrier

Diffusion coefficient (cm2/day) values
11-15
DIFDIS
  range from about  1 to  20.



Diffusion distance  (cm).
                                 186

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Column
No.
16-20
21-25
26-30
31-35
36-40
41-45
46-50
51-55
56-60
61-65
Var
type
I
I
R
R
R
R
R
R
R
R
Var
name
MIN
M0UT
SHCA
SHMG
SHNA
SHC03
SHHC03
SHCL
SHS04
SHN03
66-70
R    TRTME
Card 2 of 2

 1-10          R    CLGT(L)
11-20
R    CLGT(L+1)
               Variable
             description

First element of outside tube con-
  tacting barrier (as measured from
  surface of water table).

Last element of outside tube con-
  tacting barrier.

Concentration of Ca** in barrier water
  (mg/1)•

Concentration of Mg*4" in barrier water
  (mg/1).

Concentration of Ha* in barrier water
  (mg/1).

Concentration of C03= in barrier water
  (mg/1).

Concentration of HC03~ in barrier water
  (mg/1).

Concentration of Cl~ in barrier water
  (mg/1).

Concentration of S0^= in barrier water
  (mg/1).

Concentration of N03~ in barrier water
  (mg/1).

Travel time to displace one slug in tube
  contacting barrier (days).
Length of contact of element L with
  barrier (cm).

Length of contact of element L with
  barrier (cm).
                                  187

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  Column
    No.
 Var
type
                           Variable
                         description
CARD GROUP 5 - Stream Tube Data

Card 1 of MAXTU

 1-10          R    TUVEN(I)
11-20
21-30
                   Pore volume of tube  (feet3/foot of
                     drain).  Where 1=1 corresponds to
                     the tube closest the drain and
                     I = MAXTU to the tube farthest
                     from the drain.
  R    TUWEN(I)    Width of tube at the water table  (feet).
31-40
  R    THETA(I)
       MAX(I)
            Volumetric moisture content of the tube
              at saturation.  It is the ratio of the
              volume of water to the volume of soil
              (dimensionless).

            Number of elements or segments that the
              tube is to be divided into.  (Program
              limits this value to 25 or less.)
Note:  One card is needed for each tube.

CARD GROUP 6 - Soils Analysis Data

This group is only included for an initial run  (IRERUN ?  1) •  There
will be one card per tube if each tube is homogeneous  (ISAME =  1)  or
one card per element in all tubes (MAX(I) card  for tube I)  if each
tube is nonhomogeneous (ISAME $ 1).  Cards should be in order,  start-
ing with tube 1 nearest the drain and ending with tube MAXTU farthest
from the drain.  Where there is one card per element, cards for a
given tube should start with element 1 nearest  the water  table  and
end at element MAX(I) nearest the drain.  (See  Figure 25.)  Note that
element boundaries are not necessarily horizontal.  This  means  that
care must be taken when assigning soil chemistry data to  each element.
Most of the chemistry data comes from a soil extract analysis.
Card 1 of 2

 1-5
  R
CA(J)
(J denotes the element number.)

Calcium (Ca++) concentration  (meq/1).*
  Meq/1 denotes miHiequivalents per  liter.
                                188

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  Column
    No.

 6-10
11-15

16-20

21-25

26-30

31-35


36-40

41-45

46-50


51-55
 Var    Var
type   name

  R    AMG (J)
56-60



61-65



66-70


71-75


76-80
  R

  R

  R

  R

  R


  R

  R

  R
  R
  R
  R
ANA(J)

ANH4(J)

CL(J)

S04(J)

HC03(J)


C03(J)

AN03(J)

EC(J)
  R    CAL(J)
  R    XX5(J)
  R    XTRCT(J)
BD(J)


AKCS(J)


AKCM'(J)
               Variable
             description

Magnesium  (Nig**) concentration
   (meq/1).

Sodium  (Na4"1") concentration  (meq/1).

Ammonium  (NHi/) concentration (meq/1).

Chloride  (Cl~) concentration  (meq/1).

Sulfate (SO^3) concentration  (meq/1).

Bicarbonate  (HC03~) concentration
   (meq/1).

Carbonate  (C03=) concentration  (meq/1)

Nitrate (NOa") concentration  (meq/1).
Cation exchange capacity  (meq/100 gm
  of soil) .

Indicator as to whether soil is cal-
  careous (lime present).
If Cal(J) = 1.0, soil is calcareous.
If CAL(J) = 0.0, soil is noncalcareous.

Gypsum (CaS04 • 2H20) content (meq/100 gm
  of soil) .  Residual gypsum content at
  moisture percentage of extract.

Ratio of water to soil at which the
  soil extract was made, expressed
  as a decimal (gm water/gm soil) .

Bulk density of the soil  (gm of soil/ cm3
  of soil) .

Ca-Na exchange coefficient (if the
  default values are not wanted) .

Ca-Mg exchange coefficient (if the
  default values are not wanted) .
                                  189

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  Column      Var    Var                       Variable
    No.      type   name                     description

Card 2 of 2

 1-10          R    PC02(J)     C02 partial pressure  in  atmospheres.

Restart Deck

These cards are punched at the end of a run if IPUNCH =  1.  They are
reread on a restart run (IRERUN = 1) in which case  initial  soils data
(group 4) are deleted.  The cards are punched by  the  statement:

   PUNCH (IFMT) JYEAR, KC0UNT, (ANH4(J), AN03(J), UREA(J),  CA(J),
   ANA(J), AMG(J), HC03(J), CL(J), C03(J), S04(J),  EC(J), XX5(J),
   CAL(J), E5(J), C5(J), SA5(J), CAS0(J), AGS0(J),  BNH4(J),
   CMH201(J), BD(J), HK(J), AZE(J), J=l ,N) .

where IFMT = 2I5/(6E13.5/6E13.5/6E13.5/3E13.5, I5.E13.5)
followed by PUNCH(JFMT)    (H0LD (L),L=1,10)
where JFMT = 6E13.5/4E13.5.

The above cards are repeated for each tube.  It is  seen  that  there  are
3+4xMAX(I) cards per tube for a total of MAXTU (3+4xMAX(I)) cards for
all tubes.  The variable definitions follow:

   JYEAR - Current year number.

   KC0UNT - Number of slugs out this tube so far.

   J - Element or segment number within the tube.   It goes  from
        1 to N where N is MAX(I).

   ANH4(J) - Mass of ammonium nitrogen (NH^-N) in element  (ug)*.

   AN03(J) - Mass of nitrate nitrogen (N03-N) in  element (ug).

   UREA(J) - Mass of urea nitrogen (Urea-N) in element (ug).

   CA(J) - Mass of calcium (Ca"1"*) in element (ug).

   ANA(J) - Mass of sodium (Na+) in element (ug).

   AMG(J) - Mass of magnesium (Mg**) in element (ug).
* ug denotes 10~6 gms or micrograms.
                                 190

-------
HC03(J) - Mass  of bicarbonate (HC03-) in element (ug).

CL(J) - Mass of chloride (Cl~)  in element (ug).

C03(J) - Mass of carbonate (C03=) in element (ug).

S04(J) - Mass of sulfate (SOU=)  in element (ug).

EC(J) - Exchange capacity of element (eq/gm).

XX5(J) - Gypsum (CaSCV2H20) concentration in element (moles/gm).

CAL(J) - Lime indicator for element as  used on input for initial
           soils analysis.
         If CAL(J)  =  1.0, lime  is present.
         If CAL(J)  =  0.0, lime  is not present.

E5(J) - Exchangeable  calcium (Ca"1"*) in  element (moles/gm).

C5(J) - Exchangeable  magnesium  (Mg++) in element (moles/gm).

SA5(J) - Exchangeable sodium (Ma*) in element  (raoles/gm).

CAS0(J) - Undissociated gypsum  (CaSO^)  in element (moles/1).

AGS0(J) - Undissociated magnesium sulfate (MgSO^) in element
             (moles/1).

BNH4(J) - Exchangeable  ammonium  (NH^*)  in element (moles/gm).

CMH201(J) - Water content in element (cm3).

BD(J) - Soil bulk density of element (gm/cm3).

IIK(J) - Lime indicator for element as  used  internally.
         If IIK(J)  =  1,  lime is  present.
                          }•'•
AZE(J) - Value  proportional to  intercept of  the  equation  relating
           pC02 and soil moisture content.(5)  A constant for  each
           soil computed from the extract analysis.

H0LD(L) - Accumulated masses of  various inputs to the saturated
            system that were left over  after the last slug  output
            was  computed.   For future runs,  these partial sums are
            used to initialize the mass counters until  a  volume of
            water sufficient to  displace the water  in one element
            has  been  accumulated.
                               191

-------
   H0LD(1) - Volume of water (cm3/cm of drain).

   H0LD(2) - Mass of calcium (Ca"1"1") (ug/cm of drain).

   H0LD(3) - Mass of magnesium (Mg++)   (ug/cm of drain).

   H0LD(4) - Mass of sodium (Na*)  (ug/cm of drain).

   H0LD(5) - Mass of ammonium nitrogen (NH^-N) (ug/cm of drain).

   H0LD(6) - Mass of chloride (Cl~) (ug/cm of drain).

   H0LD(7) - Mass of sulfate (S01+=) (ug/cm of drain).

   H0LD(8) - Mass of bicarbonate (HC03~) (ug/cm of drain).

   H0LD(9) - Mass of carbonate (C03=)   (ug/cm of drain).

   H0LD(10) Mass of nitrate-nitrogen (N03-N) (ug/cm of drain).

TAPE INPUT

Magnetic tape output from the unsaturated chemistry program  (unit  2)
can be used to input deep percolation data to the saturated  chemistry
program (unit 15).  This tape contains the volume of water leached from
the unsaturated zone and the corresponding mass of salts leached by
constituents.  Values are expressed on a per-unit area basis.  The
tape is written without format (binary) and is structured as shown in
Figure 28.

Each file represents a year of data.  In executing the saturated
chemistry program, only full years are used.  To allow for restarts,
the user specifies the initial file (INFIL15) to be used as  input  for
the first year computed by this run as well as the last file  (LSFIL15).
The program skips the first (INFIL15-1) files and positions  for the
initial read of the first logical record in INFIL15.  The program  then
reads and executes through subsequent files until LSFIL15 has been
read.

This last file may be repeatedly reread for future years' input by
using the NREPT option.  If NREPT  - 1, the program rereads and uses
data in LSFIL15 a total of NREPT times.  Logically, the user may wish
to use this option if the data in  LSFIL15 represent either an average
year or the results when a "dynamic" equilibrium condition is attained.

When deep percolation data are input by cards  (ICARD = 1), the inputs
are written on unit 15 using the same file structure as for  magnetic
                                 192

-------
      B0T (beginning of tape
        ,Ioad po i nt
                                   E0F (end of  file
                                          mar k


^




first


i

second
1 og i ca

last


records
^

»

'/.

i\
L.

^ 	 '
^ !

1  f iIe/year,  1st  year
                                2nd  year
3rd year    etc.
  Each  Iog i caI
    yRITE(2)
    where  1 YEAR
           1 DAY
           SUM0UT
           DELN

           AMT(I)
          DEL(I)
         record is  written  by  the binary write statement:
        1  YEAR, I  DAY,  SUM0UT, DELN, (AMT(I),  DEL(I)  I=I,IO)
             is the year  number
             i s the Ju I i an  day                      ,   ->
             is the accumulative  leachate volume  (cnr/crrr)
             is the deIta-leachate volume since previous
               record was written (cm /cm )
             is the cumulative mass of constituent  1  leached
               since the  start of the run per  unit  area (10 *
               err/ or ug/gm )
             is the mass  of constituent  I  leached since the
               last logical  record was written per  unit area
               (10 °gm/cm  or  ug/crrr)
                                                                  gm/
  Const i tuents:   I
                  1
                  2
                  3
                  4
                  5
                           Item            I
               nitrate-nitrogen  (NOj-N)    fe
               ammonia-nitrogen  (NH^-N)    7
               urea-nitrogen  (Urea-N)      8
               calcium (Ca++)              9
               sod i urn (No )               10
         I tern
  magnesium
  bicarbonate  (HCO-p
  chloride  (Cl~)
  carbonate  (C0-i=)
  sulfate  (SO/, = )
FIGURE 28  ORGANIZATION OF TAPE 2 OUTPUT FROM UNSATURATED
                       CHEMISTRY  SUBMODEL
                                  193

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tape.  In this case, inputs do not  include urea.   Individual  card val-
ues correspond to the delta amounts written on  the tape.   Since these
are the only values used by the saturated chemistry program,  the accu-
mulative values are not computed.  The month  and date  are  first con-
verted to the Julian day which is then written  along with  the year and
delta amounts on unit 15.  Cumulative values  plus  the  delta amount for
urea are written as dummy variables.

When card input is used, LSFIL15 is also the  total number  of  files or
years of input data.  The first year is written as file  1,  the second
as file 2, etc.  Once data are transferred to unit 15, INFIL15 and
NREPT are used as they were with tape input.  It is  also noted that
the user can equip a magnetic tape on unit 15 and  save the  created
files for future use.

Finally, it is noted that there are no restrictions  on the  number of
logical records in a file on unit 15.  Although the  unsaturated chem-
istry program outputs results on a daily basis, this is not required.
The program reads all records in a file, using  an  end-of-file mark
check to determine when a file has been exhausted.   The number of
records in each file may also vary.

TAPE OUTPUT

Magnetic tape output is written on unit 16 and  is  intended  for input
to the drain effluent portion of the water quality model.   Individual
runs of SATCHEM produce one file on unit 16.  This file contains
results starting with the first slug reaching the  drain in  tube 1 for
the present run, followed by the second slug  in tube 1, continuing
until the last slug for tube 1 has been computed.  Results  for succes-
sive tubes up to MAXTU follow.  When all tubes  and slugs are  finished,
an end of file mark (E0F) is written.  Thus,  individual files can
represent results for any number of years and the  number of logical
records per file may vary between files.

Figure 29 illustrates organization of the files and  logical records on
unit 16.  Each logical record contains the tube number, slug  number,
and the concentration of the constituents in  mgm/1.  The slug numbers
begin with slug 1 for the very first slug computed by the initial run
and run consecutively, even for restart runs.

To allow restarts, the user must specify the  initial file  to  be writ-
ten on unit 16, INFIL16.  The program then skips (INFIL16-1)  files
and positions the tape for the first write on INFIL16.  For the ini-
tial run, INFIL16 should be left blank or set to 1.
                                194

-------
 301 (beginning of tape,
    Ioad po i nt)
                E0F (end  of  file mark)
\


'//


1 -\ \ 	 1 ? ?
1 — 1 1 	 1 i$
slug 1 slug 2
tube 1 tube 2
"It
^~"~-^ og

ast
slug
tube

slug
tube 2
	 
-------
LIMITATIONS

Dimensioned storage in the program limits the problem  size  to:   a max-
imum of 10 stream tubes; a maximum of 25 elements or subdivisions per
tube.

There are no internal program checks to assure that these  limits are
not exceeded.  In addition, only full years or complete  files  on
unit 15 are processed.  It is noted that there is no limit  on  the
number of deep percolation inputs by cards or tape.

OUTPUT

Program output consists of printed listings, punched cards,  and  com-
puted results written on magnetic tape.

Printed data listed by the program on the common print file  is stand-
ard output.  It includes:

   a.  Deep percolation volumes and qualities if input is by cards
   CICARD = i)

   b.  Control card data

   c.  Salt input from barrier data (IINJE = 1)

   d.  Constituent concentrations for each tube element  at  end of
   run (IDUMP = 1)

   e.  Stream tube inputs

   f.  Initial soil analyses (if IRERUN ^ 1)

   g.  Outflow concentrations by constituents for each slug  of every
   tube

Punched card output is optional, being selected by IPUNCH =1.   It
consists of the restart deck which may be reus'ed without modifica-
tion for reruns.

Taped output on unit 16 is standard.  If a saved magnetic tape is not
desired, a physical tape should not be equipped on this  unit.
                                 196

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SIMULATION OF UNSATURATED  ZONE

The Saturated Chemistry  Submodel  can be utilized to  simulate both
chemistry and waterflow  in the  unsaturated zone.   In cases  where this
technique can be  applied,  the savings in data collection/preparation
and computer time can be substantial.

Coarse-textured and many medium-textured soils  lend  themselves to
simulation by this method.  A comparison of results  obtained using
the Unsaturated Flow and Unsaturated Chemistry  Submodels with those
obtained using the Saturated Chemistry Submodel provides a  means of
testing the efficacy of  this technique for a particular soil.

In applying the submodel to the unsaturated zone,  a  single  stream
tube can be used  to represent a one-dimensional flow path from the
soil surface to the water  table.   The tube may  be  subdivided into
some fixed number of elements or segments with  equal volumes and
spacing, or a single homogeneous  segment can be selected.

Consumptive use of water within the  root zone is  assumed to occur in
the upper most segment and water movement is assumed to occur at some
characteristic "leaching"  moisture content.   The  soil water content
at field capacity is often used for  this purpose.

The use of multiple segments in the  soil profile  adds desirable numer-
ical dispersion to the simulation.  About 10 segments per profile have
been found to add sufficient dispersion.

Output is written on tape  18 in a format suitable  for a direct read
by the Saturated  Chemistry Submodel  as tape 15.   In  the latter case,
the submodel would be used to simulate the saturated zone.

The following discussion summarizes  details  necessary to run the Sat-
urated Chemistry  Submodel  in the  unsaturated mode.

   a.  Input data can be read from tape 15 or from cards.   If tape 15
   is used, the consumptive use must already have  been removed from the
   applied water.  The program  can remove the consumptive use if cards
   are utilized.

   b.  It is possible to assign a different initial  chemistry to each
   segment by setting ISAME t 1.

   c.  Set MAXTU  = 1, unless more than one soil profile is  being sim-
   ulated per run.
                                  197

-------
d.  If IDUMP = 1, a "picture" of the unsaturated profile chemistry
will be printed at the end of the run.

e.  Set IWR = 1 so that output file tape 18 will be written.

f.  TUVEN(l) must be set equal to the occupied pore volume of the
flow tube taken vertically from the soil surface down to a fixed
water table.

For convenience, assume a 1-ft2 column of soil and compute the pore
volume occupied by water at field capacity or some other "leaching"
water content as follows:

               TUVEN(l) = DEPTH * THETA(1V
                                          fc
   Where:  DEPTH is the vertical depth to the water table (ft),
           and THETA(1)_  is the volumetric soil water content at
                       fc
           the "leaching" water content level.

g.  Set TUWEN(l) equal to 1 ft.

h.  Set THETA(l) equal to the value discussed under f. above.

i.  Set MAX(l) equal to the number of segments desired in the
in the tube (e.g. - 10).

j.  Data for the soil chemical and physical parameters should
be inserted into the input data deck with values for parameters
closest to the soil surface associated with the first element or
segment, etc.  Values for PC02 and other parameters should be
inserted to reflect the unsaturated soil profile.
                             198

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                           SECTION XVI

                          USER'S MANUAL

                DRAIN EFFLUENT PREDICTION PROGRAM

INTRODUCTION

This program  is designed to combine or mix the water qualities  and  flow
discharges  from individual stream tubes extending from the water  table
to subsurface or surface drains.

Outputs  from  the drainout, saturated flow, and saturated  chemistry  pro-
grams are used as direct inputs to compute the quality and quantity of
the drain effluent.   When the saturated chemistry portion is bypassed,
inputs from the unsaturated chemistry program are used.

In essence, the drain effluent program performs the  routing process,
modifies steady-state results when monthly discharge data are used,
performs certain computations to obtain salt  loads (masses), and  gen-
erates the  required  output.  This output includes listings  and  punched
cards.

PROGRAM APPLICATION

There are two computational methods included  in the  drain effluent
program.  The method used depends on the manner in which  the quality
input data  are developed.   Briefly, in one case the  inputs  represent
the quality of leachate water and in the other the quality  of the dis-
charges  from  the individual flow tubes.

Output from either method includes printed results.   An optional  card
output is also available when monthly drain discharges are  used.  Con-
centrations of each  parameter and salt load results  can be  selected.

There are many similarities in the inputs required by either computa-
tional method.   However,  understanding the basic differences between
the two types of quality inputs will be helpful in applying the drain
effluent program.  The two cases  are discussed below.

QUALITY OF  LEACHATE  WATER IS INPUT

When this approach is  used, chemical transformations in the saturated
zone are not  simulated and the saturated chemistry program is bypassed.
The drain effluent program merely routes the  leachate water and its
salts down  each stream tube to the drain.
                                  199

-------
Steady-state flow is assumed and piston displacement theory  is applied
to each tube.  When the quality of the leachate water is changed  at  a
given time, a "front" dividing this water from that previously enter-
ing the saturated system is assumed to form.  The front is assumed to
travel down each stream tube in accordance with the travel times  com-
puted by the saturated flow program.  The relative arrival times  of
the front at the drain for each tube are then used to combine results
from each tube yielding the drain effluent quality.

Leachate water quality inputs can be entered by card input or by  an
edited form of the taped output from the unsaturated chemistry pro-
gram.  Although card input is usually limited to testing and "debug-
ing," they can be used to input observed field data for verification
purposes.

Because the final results are based on a steady-state (average) dis-
charge, outputs from the unsaturated chemistry program must be edited
so that each change in quality corresponds to the proper volume of
leachate water.  Since the unsaturated chemistry program produces
both variable leachate volumes and qualities on a daily basis, it is
necessary to edit the data so that inputs are based on equal volumes
of water.  The corresponding average concentrations of each parameter
are then computed.  This is accomplished by a utility program called
EDITC0 (see Suggested Improvements).

When cards are used, unequal time steps may be used, with inputs only
being required each time the leachate water quality changes.  However,
the volume of water is assumed equal to that which would exist under
steady-state drain discharge.

DATA FROM SATURATED CHEMISTRY PROGRAM IS INPUT

When the saturated chemistry program is used, each stream tube is sub-
divided into a number of equal volumed segments.  Leachate water  is
accumulated until the volume corresponds to the pore volume of the seg-
ment.  The mass of each parameter is also accumulated, resulting  in a
water having the average concentration during the given time period.
This volume of water with its associated quality is referred to as a
slug.

The saturated chemistry program then passes the slug down the tube
through successive segments, simulating the various chemical trans-
formations.  The final result is the quality of water in each slug
which discharges into the drain from a given tube.  It is this dis-
charging water quality that is placed on tape by the saturated chem-
istry program and used as input to the drain effluent program.
                                 200

-------
Because  chemistry changes in the saturated system are not simulated
when  leachate water is input to the drain effluent program  the dis-
at:rwa^rWat?hifality V*1"11* "«tlcal to tS.S'S'thJ lach-
ate water.   This  is true for every stream tube.   However, when the
saturated  chemistry inputs are used, each tube will have different

                              at least until a "dynamic"
The relative  timing of each slug arrival is based on an average
drain discharge  and the corresponding travel times.   When  this is
done, results represent average qualities for equal  increments of
discharge.  However,  monthly drainage volumes determined by  the
drainout program can  be used to modify the steady-state results.
The variable  discharge pattern is then used to compute  the average
monthly concentrations.

UNIT NUMBERS

Six logical unit numbers are referenced when the  quality of  leachate
water is input:   S, 6,  7,  8,  16 and  29.   When the saturated  chemistry
results are used as input  there are  7+NST units referenced:  S, 6, 8,
9, 16, 29, 62, and MUNIT = 16+1 to 16+NST where NST  is  the number of'
stream tubes.  Since  the maximum number of stream tubes  is 10, the
maximum number of units  is 17.
Unit numbers are:

    Unit
designation
Unit description
   or purpose
               The common input tape or unit (CIT).
               puter systems standard input device.

               The common output tape or unit (C0T).
               puter systems standard output device.
                   It is  the corn-
                    It is  the  com-
               The unit on which the "formula" or equation giving the
               composition of the drain effluent is written (see
               Suggested Improvements).  It is only used when the
               leachate water quality is input.  This is normally a
               scratch unit and is written with unformated (binary)
               writes.  However, it may be equipped and saved.  Sub-
               sequent runs must specify a saved tape by setting
               I0C(7) = 1, 2, or 3.

               The unit on which all data necessary for plotting con-
               centrations or for computing the salt load results is
               written.  It is written in binary form and is usually
                                201

-------
    Unit
designation
    16
   MUNIT
             Unit description
               or purpose

considered a scratch unit although it may be  equipped
and saved for future use.  It is used when  input  is
the leachate water quality or the drain  effluent  qual-
ity, although the structure and data are slightly dif-
ferent .  For:

  input of leachate water quality (I0C(4) = 1 or  2),
  unit 8 is written when salt load results  are
  requested (I0C(5) = 1 or 2) or when a  saved tape
  is requested (I0C(6) = 1),  When I0C(7) = 2 or  3,
  then a previously generated saved tape on unit  8
  is indicated and must be included in the  run.

  input of the drain effluent quality (I0C(4) = 3),
  unit 8 is written when monthly concentrations are
  to be computed (I0C(10) = 1) provided  a request  is
  specifically made to create a saved tape  (I0C(6) =
  1).  It is used for subsequent runs by setting
  I0C(8) = 1.

The scratch unit on which the computed drain effluent
quality (composite of all tubes) for all parameters
is written each time a slug reaches the  drain.  It is
only used when the saturated chemistry results are
used as input (I0C(4) - 3).

The unit on which the tape containing the quality
inputs is mounted.   Either leachate water is input
(I0C(4) = 2) or the saturated chemistry  tape is
used (I0C(4) = 3).

Data on the magnetic tape mounted on unit 16 is not
formated and is in binary form.  The tape structure
is shown in Figure 29 for the case where the quality
of leachate water is input and in Figure 30 when  the
drain effluent quality is input.

The logical unit on which the water quality inputs
from the saturated chemistry program (as read from
unit 16 when I0C(4) = 3) are transferred.   It is  an
internal scratch unit on which the data  is written in
binary form.
                                  202

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                                                                                         NEXT PAGE
                          'PARAMETER UNITS
                            CODE
                     PARAMETER NAMES
                    (2nd. card if more than
                      6 parameters)
               'PARAMETER NAMES
          'NO. QUALITY
             CHANGES B
             PARAMETERS
Q                                          ORIGINAL GW
                                          UALITY (Znd.cardii
                                          more than 8 param.
/ TRAVEL TIMES
/NO. STREAM
f TUBES


	 1
YES

                          -CARD TYPE
START OF  INPUT DECK


 FIGURE 30. DATA  DECK STRUCTURE -DRAIN  EFFLUENT  PREDICTION  SUBMODEL
                                           203

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          END OF DATA DECK
                                  MONTHLY DISCHARGE
                                    DATA {2 cords per
FIGURE so. (CONTINUED;
              204

-------
    Unit
designation
                  Unit description
                     or purpose

     The data for each stream tube are placed on different
     units with MUNIT starting one higher than 16, being
     incremented by one for each additional tube.  Thus:

                 MUNIT =16+1 for stream tube 1
                 MUNIT =16+2 for stream tube 2
                            MUNIT a 16 +  NST  for  stream  tube NST

               Since  NST has  a maximum value of  10, MUNIT will range
               from 17  through 26.

    29         The unit to which plotter commands  are written when
               the plot subroutines are  included in the model.  This
               corresponds to the default unit number when the CRT
               unit is  not specified by  the  user.

    62         The card punch unit of the computer system.

DATA DECK STRUCTURE

There are 23  types of input cards in the input deck, as shown in Fig-
ure 30.  The  variables  are defined below.  It should be noted that not
all card groups are included  in a given  run.
CARD GROUP  1  - Title  Information
Column
  No.
 Var
type
Card 1 of  1

 1-80      A
         TITLE
              Variable
             description
An 80-character alphanumeric title used
  to identify all printed and plotted
  output.  If this title is desired to
  be centered on output, it must be cen-
  tered on the card.
                                  205

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Column
  No.
           Var
          type
               Variable
              description
CARD GROUP 2 - Problem Selection
Card 1 of 1

 1         I
 2         I
40
                   IPR0B(1)     A control array which calls the proper
                   IPR0B(2)       overlay for execution.  Individual
                                  programs in the water quality model
                                  were originally designed for inclu-
                                  sion in an overlay system.  Presently
                   IPR0B(40)      only the saturated flow and drain
                                  effluent portions are included.  When
                                  IPR0B(I) is set to 1, the Ith overlay
                                  is called.  The program will accept
                                  up to 40 entrys.   Thus:

                                  IPR0B(1) = 1, call the saturated flow
                                                 routine
                                  IOR0B(2) = 1, call the drain effluent
                                                 routine

                                On output, values of IPR0B(I) are listed
                                  as I0C values under the heading PROB-
                                  LEM CONTROL INFORMATION FOR MAIN
                                  PROGRAM.
CARD GROUP 5 - Input/Output Options
Card 1 of 1

 1         I
 2         I
                   I0CC2)
                   I0C(40)
An input/output option array used to
  specify the type of inputs, the
  required computations and the
  printed and plotted output.  (See
  Input/Output Options for details.)
40         I

CARD GROUP 4 - Number of Stream Tubes
Card 1 of 1

 1-10      I
                   NST
The number of stream tubes to be used.
  When the saturated chemistry output
  is used, NST must correspond to the
  number used in the saturated chemis-
  try program.
                                  2O6

-------
Column
  No.
 Var
type
 Var
name
 Variable
description
CARD GROUP  5  - Travel  Times
Card 1 of  1

 1-8       R
 9-16      R
73-80       R
         TRAVEL(1)
         TRAVEL(2)
         TRAVEL(10)
              Time of  travel assuming piston displace-
                ment down tube  I  (years).   1=1
                corresponds to  the tube nearest the
                drain,  I = 2 to the next closest tube,
                etc.   These values are computed by the
                saturated flow  program and  are part of
                its output.  Up to 10 travel times can
                be included.
CARD GROUP  6 -  Number of Quality Changesand Parameters

Card 1  of 1
  1-5
  6-10
 R
 NUQUCH       The number of changes  in the quality of
                 the  leachate water when either cards
                 are  used to input quality  (I0C(4) = 1)
                 or when input  is from the unsaturated
                 chemistry program (I0C(4) = 2).

              When input is the saturated chemistry
                 program results (I0C(4) « 3), NUQUCH
                 is the maximum number of slugs leav-
                 ing  any tube.  It will always corre-
                 spond to tube  1.  The value is obtained
                 from the saturated chemistry programs
                 printed output.

 NUQUPA       The number of quality  parameters being
                 considered.  It includes the number
                 of anions plus the number of cations,
                 but  does not include the total load.
                 NUQUPA must correspond to the number
                 of parameters  used in the unsaturated
                 or saturated chemistry programs  when
                 their output is used.  NUQUPA must be
                 in the range 1 <_ NUQUPA £ 15.
                                 207

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Column
  No.
 Var
type
CARD GROUP 7 - Parameter Names

Card 1 of N

 1-10      A       APANAM(l)
71-80      A       APANAMC8)
(All fields may not be used)
Card N of N

 1-10      A
               Variable
              description
                      A 10-character alphanumeric name used
                        to identify the quality parameter,
                        where I « 1 to NUQUPA.  (N = 1.)  If
                        NUQUPA exceeds 8, two cards are
                        required (N * 2):  the first giving
                        APANAM(l) - APANAM(8) and the-second
                        giving APANAM(9) - APANAM(NUQUPA).
                        These labels are used to identify all
                        printed and plotted output, and should
                        be in the same order as the quality
                        inputs coming from cards (I0C(4) = 1)
                        or from the chemistry programs
                        (I0C(4) = 2 or 3).
         APANAM(9)
61-70      A       APANAM(IS)
(All fields may not be used)

CARD GROUP 8 - Parameter Units Code
Card 1 of 1

 1         I
 2         I
         lUNIT(l)
         IUNIT(2)
15         I       IUNIT(15)
(All fields may not be used)
A numeric units code for parameter I
  where the order is identical to that
  for APANAM(I) and the quality inputs,
                                If IUNIT(I) -
                                IUNIT(I)
                                    1, the units are in
                                         milligrams/liter.
                                         (On output they
                                         are labeled MG/L)
                                    the units are in
                                      milliequivalents/liter.
                                      (On output they are
                                      labeled MEQ/L.)
                               208

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Column
  No.
 Var
type
                            Variable
                           description
CARD GROUP 9  - Original  Ground Water Quality

Card 1 of N
11-18
19-26
 R
 R
QUAL(l)
QUAL(2)
67-74      R        QUAL(8)
(All fields may  not be used)
Card N of N

11-18      R
19-26      R
         QUAL(9)
         QUAL(IO)
59-66      R        QUAL(15)
(All fields may not be used)
CARD GROUP  10  -  Reference Time
Card  1 of  1

 1-10      R
         TIMREF
The initial or original quality of the
  ground water at the start of the run
  for parameter I where the order is
  identical to that for APANAM(I) and
  the other quality inputs.  Units for
  the initial quality must correspond
  to those specified by IUNIT(I).
If NUAUPA <_ 8, N = 1
If NUAUPA > 8, N => 2
             If there are more than 8 parameters,
               2 cards must be used with the first
               giving QUALI(l) - QUALI(8) and the
               second QUALI(9) - QUALI(NUQUPA).

             It is noted that the original ground
               water quality is only used when the
               saturated chemistry results are not
               used.  Since chemical transformations
               are not simulated and piston displace-
               ment is assumed, the leachate water
               is merely routed to the drains.  The
               aquifer is assumed to be homogeneous
               with respect to water quality and the
               quality of the drain discharge will
               be identical to the initial quality
               until the first front reaches the
               drain.
             The reference time to be used as the
               initial time at the start of the run
               (years).  It must be consistent with
               times on the type 11 and type 12
               cards.  TIMREF could be 0.0, 1974,
               etc.
                                 209

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Column
  No.
 Var
type
                            Variable
                           description
CARD GROUP 11
Leachate water quality changes Group N cards must be arranged in chron-
ological order, starting with the first change and ending with the last
change (NUQUCH).
Card 1 of N
 1-10
         TIQUCH(I)
11-18
19-26
 R
 R
PPM (1,1)
PPM(I,2)
67-74      R       PPM(I,8)
(All fields may not be used)
Card N of N
The time of water quality change I
  (years).  It must use the same time
  base as TIMREF.  Thus, if TIMREF =
  1974 and the first change is half-way
  through the first year, TIQUCH(l) =
  1974.5 years.

The quality of parameter J for the Ith
  change.  Units correspond to those
  specified on the group 8 card.  Param-
  eters are arranged in the same order
  as APANAM(J) and the other inputs.
  It is noted that PPM(I,J) is the
  actual quality at this time, rather
  than an incremental or delta value.

If there is no change for a given param-
  eter at this time, the corresponding
  PPM(I,J) may be left blank.  The pro-
  gram will then use the previous value.
  Thus, only parameters actually experi-
  encing changes need be punched on
  cards.

If there are more than 8 parameters,
  two Group 11 cards are required.  The
  first card will contain quality for
  parameters 1 through 8 while the sec-
  ond contains quality for parameters
  9 through NUQUPA.
                                210

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Var
Column
  No.
CARD GROUP  12  -  Finishing Time

Card 1 of 1
                                     Variable
                                    description
 1-10
R
TIMFIN
The time at which the run is terminated
  (years).  It must use the same time
  base as TIMREF.  For example, if a
  16-year run is desired and TIMREF =
  1974, TIMFIN = 1974 + 16. = 1990.
CARD GROUP  13  -  Unsaturated Chemistry Tape Information
Card  1  of 1
 1-5
         NINTYR       The number of equal  time  intervals
                        per year on the special unsatur-
                        ated chemistry tape produced  by
                        the utility program EDIT0.   (See
                        Figure 30 for tape for  mat.)
CARD  GROUP 14 - Saturated Chemistry Tape Information
Card  1  of 1

  1- 5      I
         NINTYR
  6-10
         NFILE
             The number of elements or segments that
               each  stream tube was divided into in
               running the saturated chemistry pro-
               gram.   (For example, if 0.1 pore vol-
               umes  were used, NINTYR would be 10.)
               It is noted that although the satu-
               rated chemistry program allows for a
               different number for each tube, the
               drain effluent program requires the
               same  number.

             The number of files of data on the sat-
               urated  chemistry output tape that are
               to be read  [3, Tape Output].  Individ-
               ual runs of program SATCHEM produce
               one file.  The organization of each
               file  is shown in Figure 29.
                                  211

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Column
  No.
 Var
type
                            Variable
                           description
CARD GROUP 15 - Number of Slugs for Each Tube on Tape

Card 1 of 1
 1- 5
 6-10
         N0SLUG(1)
         N0SLUG(2)
46-50      I       N0SLUG(10)
(All fields may not be used)
             The total number of slugs of water
               reaching the drain that are contained
               on the saturated chemistry input tape
               where 1=1 corresponds to the tube
               adjacent to the drain, I = 2 to the
               next closest, etc.  The values of
               N0SLUG(I)  are obtained from the
               printed output of the saturated chem-
               istry program, or from tape unit
               written by saturated chemistry.
CARD GROUP 16 - Combining Weights

Card 1 of N
 1-10
11-20
 R
 R
C0MWT(1)
C0MWT(2)
71-80      R       C0MWT(8)
(All fields may not be used)
Card N of N

 1-10      R
11-20      R
         C0MWT(9)
         C0MWT(10)
61-70      R       C0MWT(15)
(All fields may not be used)
The combining weight of parameter I
  where the order is identical to that
  for APANAM(I) and the other quality
  inputs.  The combining weights are
  equal to the atomic weight divided
  by the valence and are used to con-
  vert qualities in milliequivalents/
  liter to milligrams/liter.

When quality inputs are by cards and
  the units specified by IUNIT(I) are
  in milliequalvalents/liter for one
  or more parameters, then the combin-
  ing weight card is required.  Only
  the combining weights for those
  parameters expressed in MEQ/L need
  be included with the others left
  blank.
             When there are more than 8 parameters,
               two cards must be included.  The
               first will contain combining weights
               for parameters 1-8 and the second
               for parameters 9 - NUQUPA.
                                 212

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Column
  No.
 Var
type
               Variable
              description
CARD GROUP  17  -  Steady-state Drainage Data

Card 1 of 1
 1-10
11-20

21-30
 R       Q            The steady-state drain discharge
                         (cubic feet/year/foot of drain).  It
                         is the total discharge from the aqui-
                         fer on both sides of the drain.  The
                         numerical value can be obtained from
                         the saturated flow program's printed
                         output.

 R       SPACE        The horizontal drain spacing (feet).

 R       V0LUME       The volume of water stored in the aqui-
                         fer from the water table to the bar-
                         rier between drains (cubic feet/foot
                         of drain).  When all salt load com-
                         putations are requested (I0C(5) = 2),
                         the V0LUME must be included.   Other-
                         wise the program will not use it.
CARD GROUP  18  -  Total Load Array
Card 1 of  1

 1         I
 2         I
         ISARRY(l)
         ISARRY(2)
15         I        ISARRY(15)
(All fields may not be used)
A flag used to indicate which parameters
  are to be included in the T0TAL L0AD,
  where I is the parameter in the same
  order as APANAM(I) and the other qual-
  ity inputs.  If:
ISARRY(I) = 1, then include this param-
                 eter in the T0TAL L0AD.
ISARRY (I) ? 1, then exclude this param-
                 eter from the T0TAL
                 L0AD.
CARD GROUP 19 - Number of Years  of Monthly  Discharge  Data
Card 1 of 1

 1- 5      I
         NYEARS       The number of years of monthly discharge
                        data that are to be read.  These data
                        are contained on the type 21 cards
                        which are output from the drainout
                        program.
                                213

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Column     Var     Var                         Variable
  No.     type    name                        description

CARD GROUP 20 - Steady-state Discharge

Card 1 of 1

 1-10      R       Q            The average yearly drain discharge used
                                  to calculate arrival times in the sat-
                                  urated flow program (acre-feet/acre/
                                  year).

CARD GROUP 21 - Monthly Discharge Data

These cards are output from the drainout program, except for the title
card which is eliminated.

Card 1 of M

 1-5      I       IYEAR        The year number of the data.

 6-7      I       ICRD         The card order within the year. ICRD = 1
                                  contains data for the first 6 months
                                  and ICRD = 2 contains data for the
                                  second 6 months.

 8-19      R       QM0N(1)      The monthly drain discharge for month I
20-31      R       QM0N(2)        where I = 1 is January, I = 2 is Feb-
                                  ruary, etc. (acre-feet/acre/month).
 •         *          *
 *         *          *
           R

CARD GROUP 22 - Microfilm Identification

The model version included in Volume V does not include plot sub-
routines.  However, a blank card must be added here.

CARD GROUP 23 - Fiche Header Card Information

Fiche capability not included in this version of the model.  No card(s)
needed.

Input/Output Options

Individual input, computation, and output options are specified by
setting the appropriate I0C(I) variable to the desired value on the
                                 214

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group 3 card.  For many options,  the variables act as switches with
a value of 1 turning  the option on and any other value leaving it off.

Except for I0C(21) which controls card output individual printed output
options are selected  by the I0C(11) - I0C(25) variables.  An individual
option is selected by setting the I0C(I) value to 1.  All of these
options, except  for I0C(21) can be selected by setting 100(1)  = 1.
This eliminates  the need of turning the individual options on.

Plotted* output  options are selected by the I0C(26) - I0C(40)  variables.

The two basic methods of inputing water quality changes are selected by
the I0C(4) option.  When I0C(4) = 1 or 2 the quality of leachate water
is used (i.e. water leaving the unsaturated zone) and if I0C(4) = 3 the
drain effluent quality is used (i.e., results computed by the  saturated
chemistry program).   Some options are used for both cases while others
apply to only one.  Tables 16 and 17 summarize this information and
include a list of options that are presently unused.  Restrictions in
the use of each  option are also noted in the following list.

                                        Option

                       Select all print options, I0C(11) - I0C(25).
                       (I0C£21) is not included since it is a punch
                       option)

 2       1             Select all plot options, I0C(26)  - I0C(40).

 3       1             Read all required saturated flow data from cards.
                       This includes the number of stream tubes (card
                       type 4), the travel times (card type 5)  as well
                       as the steady-state discharge, drain spacing and
                       volume of water in storage (card type 17) when
                       the leachate water quality is input (I0C(4)  =
                       1 or 2) and salt load computations are requested
                       (I0C(5) = 1 or 2).

 3      ^i             The above data are expected to be in C0MM0N stor-
                       age as a result of running the saturated flow pro-
                       gram first.

 4       _             This option controls the manner in which quality
                       inputs are made to the program.

 4       i             The quality of the leachate water is input via
                       cards (card type 11).
* Plot routines  are available,  but were not included in the model,
                                    215

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TABLE 16.   DRAIN EFFLUENT PREDICTION PROGRAM

           Input/Output Option Summary


                  Available options
IOC(I)
option
1 =
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
Leach ate
input
IOC (4) = 1 or 2
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Drain effluent
input
IOC (4) = 3
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Unused
options
X
X
X
X
                                                   Graphical
                                                   output  options
                                                   not included in
                                                   this version of
                                                   the model.
                            216

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  TABLE  17.  DRAIN EFFLUENT PREDICTION PROGRAM

          Salt  Load Considerations When
         Drain  Effluent Quality is Input
                   (I0C(4)  = 3)
Accumulative
Item
Compute


Print
Plot
Monthly
I0C(5) = 1
or
I0C(5) = 2
I0C(17) = 1
**
Annual
I0C(5) = 1
or
I0C(5) = 2
I0C(18) = 1
**
Rates*
Monthly
I0C(5) = 2


I0C(17) = 1*
**
Annual
I0C(5) = 2


I0C(18) = 1*
**
* Rates cannot be  output  unless  computed.   Thus,  if
I0C(5) ? 2, the program ignores  the I0C(17),  I0C(18),  and
I0C(32) commands to  output  nonexistent  results.
**  Plot capability  not included in this  version  of  the model,
but can be added  (see  Graphical  Output).

                                          Option

                       The quality of the  leachate water is  input via
                       magnetic tape from  the  special ability program
                       EDITC0 - mounted  on unit 16, with the format
                       given on Figure 30.

                       The quality of the  drain effluent is  input via
                       magnetic tape from  the  saturated chemistry pro-
                       gram  SATCHEM.  This tape is mounted on unit  16
                       with  the format as  indicated in Figure 29.

                       Quality inputs are  not  inputed and results will
                       be  meaningless.

                       In  general, this  option is  used to select the
                       computation of salt load information. The spe-
                       cifics depend on  whether quality inputs  are  for
                       the leachate water  or for the drain  effluent.
                       The I0C(5) options  are now discussed  separately
                       for each method of input.
any other
  value
                         217

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                                   Options

               Leachate water quality is input (I0C(4) = 1 or 2).
               Compute the accumulated salt load (tons/acre) in
               the drain effluent plus the average discharge rate
               of salt (tons/acre/year) on an annual basis.  The
               average annual rates for the entire run are also
               computed.  This is done for the individual param-
               eters and the T0TAL L0AD.

               Compute the accumulative salt load (tons/acre)
               and the average discharge rates of salt (tons/
               acre/year) for both the leachate water and the
               drain effluent.  The mean annual rate for the
               entire run is also included.  Results are for the
               individual parameters and the T0TAL L0AD.

               In addition, if printed results are selected
               (I0C(17) =1), mass balance results are included
               for the aquifer.  The initial load in storage
               (tons/acre) plus the change in storage and the
               salt remaining in storage (tons/acre) are com-
               puted for each year of the study on an accumu-
               lative basis.  This is done for each parameter
               and the T0TAL L0AD.
any other      This option is bypassed.
  value
               Drain effluent quality is input (I0C(4) = 3).
               If a saved tape 8 from a previous run is not
               being used (I0C(8) $ 1), the I0C(10) = 1 option
               must be included for the run.   Logically, both
               the I0C(8) = 1 and I0C(10)  = 1 options should
               not be used in the same run.  If they are, data
               from tape 8 supercedes that computed by the
               I0C(10) = 1 option for this run.

               Compute the accumulative salt load in the drain
               effluent (tons/acre) using monthly data on both
               a monthly and on an annual basis.  Results for
               the individual parameters as well as the T0TAL
               L0AD are included.  Monthly results are listed
               if I0C(17) = 1 while annual results are listed
                           218

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                                         Options

                       if I0C(18) = 1.  Both monthly and annual results
                       are plotted if I0C(30) =1.*

                       Compute the same results as for I0C(5) = 1 and
                       in addition compute the rate of salt load removal
                       in the drain effluent (tons/acre/year) using
                       monthly data on both a monthly and on an annual
                       basis.  Results for the individual parameters,
                       as well as the T0TAL L0AD, are included.  Monthly
                       results are listed if I0C(17)  = 1 while annual
                       results are listed if I0C(18)  = 1.  Both monthly
                       and annual results are plotted if I0C(32) =1.*
       any  other      This option is bypassed.
         value
                       Write a saved tape 8 containing the date of the
                       run,  title card, parameter name, parameter units
                       code, parameter units label,  and the computed
                       concentration for each time and parameter.   The
                       data are written in unformated form, with a sep-
                       arate file structure depending on the manner of
                       quality inputs.  When the drain effluent quality
                       is input (I0C(4) = 3), the I0C(6) = 1 option is
                       only available when monthly drain discharge data
                       are used (I0C(10) = 1).   There are no restrictions
                       when the leachate water quality is input (I0C(4) =
                       1 or 2).

                       The saved tape 8 may be read  in subsequent  runs by
                       proper use of the I0C(7)  and  I0C(8)  options when
                       the quality of leachate water is input.   When the
                       drain effluent quality is input, tape 8  usage is
                       controlled by the I0C(8)  option.

                       This  option is only available when the leachate
                       water quality is input (I0C(4)  = 1 or 2).   When
                       the drain effluent quality is input (I0C(4)  = 3),
                       this  option is bypassed regardless of the value
                       of I0C(7).
* When plots are  requested,  the accumulative results  and rates  appear
on the same graph.   Because  of the  scaling and plotting  process,  the
salt load discharge  rates  cannot be plotted unless  the accumulative
salt load is.  Consequently,  when I0C(5)  = 2 and I0C(32)  =  1, the
accumulative salt load  is  also plotted even though  I0C(30)  /  1.
                                   219

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       Value                              Options

                      An "equation"  or "formula"  for the quality of the
                      drain effluent in terms  of  each change in quality
                      of the leachate water  is first developed.*
                      These compositions or  results  are  written on
                      unit  7.   Normally unit 7 is  a  scratch  unit.
                      However,  when  there are  many changes,  data may
                      overflow  the disks requiring that  a tape  be used.
                      This  slows program execution because the  unit is
                      rewound for each parameter.

         1            Use a previously prepared tape 7.   However,  all
                      data  must be read as though  this tape  were not
                      available, including quality changes.   Computa-
                      tions start with the first parameter,  the concen-
                      tration of each being  computed with time.   The
                      I0C(8)  value should be set  to  zero or  left blank
                      in this case.

         2            Follow the procedure indicated by  the  I0C(7)  = 1
                      option, except computations  do not resume with
                      the first parameter.  Instead, computations  begin
                      with  the  parameter following the last  one com-
                      puted and already written on a saved tape 8.   The
                      number of the  last parameter is given  by  the
                      value of  I0C(8).

         3            Skip  the  generation of information on  tapes 7 and
                      8 and go  directly to the computation of the salt
                      load  results selected  by the I0C(5) option.   A
                      saved tape 8  (but not  tape  7)  is required.  All
                      inputs, including quality changes, are still
                      required.

       any other      Follow the normal computation  process  starting
         value        at the beginning of the  problem.   Data will be
                      generated and  written  on unit  7.

         ?            The use of the I0C(8)  variable depends on the
                      manner of quality inputs.  Where the leachate
                      water quality  is input,  the I0C(8) value  should
                      be set to the  number of quality parameters for
                      which results  have been written on a saved tape 8,
                      The program reads over the  required number of
* The present program method is computationally inefficient when the
number of leachate water quality changes is large.  (See suggested
improvements.)


                                 220

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         Value
        any other
          value
 records  on  tape  8  in preparation  to adding  new
 data.*   (See  I0C(7) option.)

 If I0C(7) * 0 or 1, I0C(8) should be  zero or
 blank    If  100(7)  . 2, then I0C(8)  must be  set
 properly.   If I0C(7) = any other  value, the
 value of I0C(8)  has no effect.

 When the drain effluent quality is  input
 UPH.4) = 3), a saved tape 8 is to be read.
 Computations commence with salt load calcula-
 tions.  Thus,, the I0C(8)  option is  logically
 used only when I0C(5)  = 1 or 2.  The input
 deck is then truncated.  Tape 8 mush have been
 created in a previous  run by setting I0C(10) = 1
 and I0C(6)  = 1 when I0C(4) =  3.

 This  option is not  used.
        any other
          value
 10
 This  option is  only available  when  the  leachate
 water quality is  input  (I0C(4)  =  1  or 2)  and
 salt  load  computations  are  requested  (I0C(5) = 1
 or  2).

 Compute the average yearly  concentrations of the
 drain effluent when I0C(5)  = 1  or 2 and/or the
 leachate water when I0C(5)  = 2.  Results can
 then  be printed using I0C(19) and plotted using
 the I0C(33)  and I0C(34) options.

This  option  is not  used.
This option is only available when the drain
effluent quality is input (I0C(4) = 3).
* Note that  the 11 format allows only a single-digit number.   There-
fore, if more  than 9 parameters are on tape 8, the program must be
modified.  (See Limitations and Suggested Improvements.)
                                 221

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 L     Value                            Options

                      Read monthly drain discharge data (card type 21)
                      (i.e., output from drainout program) and com-
                      pute monthly concentrations.  This option is only
                      used when the quality of the drain effluent is
                      input.  Additional inputs include card types 18,
                      19, 20, and 21.  Results are computed for each
                      parameter and the T0TAL L0AD.  They are listed
                      when I0C(20) = 1, plotted when I0C(26) = 1
                      and/or I0C(27) = 1, and punched when I0C(21) = 1.
                      Results are placed on a saved tape 8 when
                      I0C(6) = 1.

10     any other      This option is not used.
         value

11       1            Print travel times as read from card type 5.

12       1            Print the leachate water quality for all changes
                      inputed (I0C(4) = 1 or 2).  If I0C(4) = 3, this
                      option is ignored.

13       1            Print the arrival time of each piston displace-
                      ment front as it reaches the drain for each tube.
                      This is primarily a "debug" print.  Only the
                      first 16 fronts are printed.

                      When the drain effluent quality is input
                      (I0C(4) = 3), the word front on output corre-
                      sponds to slug or the boundary between succes-
                      sive slugs.  If there are less than 16 slugs/
                      fronts in the first tube, only NUQUCH are out-
                      puted.  If there are less than 16 slugs/fronts
                      (or NUQUCH if it is less than 16) for any of the
                      other tubes, printed results may not be meaningful.

14       1            Print the composition of the drain effluent in
                      terms of the various leachate water quality
                      inputs (I0C(4) = 1 or 2) at the time of arrival
                      of each front.  This is the information written
                      on unit 7.  This is primarily a "debug" print.
                      Only the first 16 terms in the equation are
                      written.  This option is not available when
                      I0C(4) = 3.
                                222

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                                         Options

                       Print  the values in the sorting arrays giving
                       the  arrival times, corresponding front, and the
                       corresponding stream tube numbers.   This is a
                       "debug" print and has no special headings.   This
                       option is available when I0C(4) = 1 or 2,  but
                       not  for I0C(4)  = 3.

16       1             Print  the concentration of the drain effluent
                       for  each parameter whenever a displacement  front
                       reaches the drain.  This option is  only available
                       when I0C(4) » 1 or 2, but not for I0C(4) =  3.

!7       1             Print  the load  results that are computed by the
                       I0C(5) option when I0C(4) = 1 or 2.   When
                       I0C(4) = 3, print the monthly load  results  that
                       are  computed by the I0C(5)  option.

18       1             This option is  only available when  I0C(4) = 3.
                       Print  the annual load results that  are computed
                       by the I0C(5) option.

19       1             Print  the average yearly concentrations selected
                       by the I0C(9) option (i.e., drain effluent  if
                       I0C(5) = 1 and  drain effluent plus  leachate water
                       if I0C(5) = 2).  This option is only used when
                       I0C(4) = 1 or 2, but not I0C(4) = 3.

20       1             Print  the monthly concentrations for each param-
                       eter plus the T0TAL L0AD when I0C(4)  = 3 and
                       I0C(10) = 1.  This option is not used when
                       I0C(4) - 1 or 2.

21       1             Punch  the monthly concentrations for each param-
                       eter and the total load as  well as  the volume of
                       drain  discharge.  (See Card Output.)   This  option
                       is only available when I0C(4) = 3 and I0C(10) = 1.

22-25    -             Not  presently used.

26-34    _             Graphical output options; necessary subroutines
                       have not been included in this model (see Graphi-
                       cal  Output).

35-40    -             Not  presently used.
                                 223

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Graphical Output

A graphical output package is available for use with the model but has
not been included as part of Volume V.  The package can be obtained
from the U.S. Bureau of Reclamation, Engineering and Research Center
in Denver, Colorado, Code 750.
                                224

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                           REFERENCES

(1)    Dumm, L. D-, New Formula for Determining Depth and Spacing of
      Subsurface Drains in Irrigated Lands.  Presented at Annual
      Meeting of ASAE, Chicago, Illinois, December 7-9, 1953.

(2)    Dumm, L. D., Validity and Use of the Transient-Flow Concept
      in Subsurface Drainage.  Presented at 1960 Winter Meeting
      of ASAS, Memphis, Tennessee, December 4-7, 1960.  28 p.

(3)    Dumm, L. D., The Transient-Flow Theory and Its Use in Sub-
      surface Drainage of Irrigated Land.  Water Resources Confer-
      ence, Irrigation and Drainage Division, ASCE, New York,
      October 16-20, 1967.

(4)    Dutt, G. R. and Shaffer, M. J., A Computer Model for Predicting
      Nitrate and Other Solutes of Agricultural Drain Water.   Final
      Report to U.S. Bureau of Reclamation.  The University of
      Arizona, 1972.

(5)    Dutt, G. R., Shaffer, M. J., and Moore, W. J., Computer
      Simulation Model of Dynamic Bio-Physicochemical Processes in
      Soils.  Technical Bulletin 196.  Agricultural Experiment
      Station.  The University of Arizona, 1972.  128 p.

(6)    Glover, R. E., Ground-Water Movement.  Engineering Monograph
      No. 31.  USDI.  Bureau of Reclamation,  1964.   67 p.

(7)    Jensen, M. E., Empirical Methods of Estimating or Predicting
      Evapotranspiration Using Radiation.  Evapotranspiration and
      Its Role in Water Resources Management.  ASCE Conference
      Proceedings.  December 5-6, 1966, p 49-53 and 64.

(8)    Jensen, M. E., Wright, J. L., and Pratt,  B. J.,  Estimating
      Soil Moisture Depletion from Climate, Crop,  and Soil Data.
      Transactions, American Society of Agricultural Engineers.
      September-October, 1971.  p 954-959.

(9)    Kunze, R.  J., Uehara, G., and Graham, K.,  Factors  Important
      in the Calculation of Hydraulic Conductivity.  SSSAP.
      32:760-765, 1968.

(10)   Land Drainage Techniques and Standards.  Tentative.   Office of
      Chief Engineer,  Bureau of Reclamation,  Denver, Colorado,
      February 1964.
                                  225

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(11)   Moody,  W.  T.,  Memorandum to Chief,  Division of Drainage and
      Ground-water Engineering,  Subject:   Table for Computation of
      Hooghoudt's Equivalent Depth.   July 17,  1964.  5 p.

(12)   Ribbens,  R. W.,  Report on  Water Quality  Model Developed in Con-
      nection with Interagency Wastewater Studies,  San Luis  Drains,
      California.  USDI,  Bureau  of Reclamation, Engineering  and
      Research  Center,  Denver, Colorado,  September  1970.

(13)   Shaffer,  M. J.  and  Dutt, G. R., Nitrification in Soil-Water
      Systems:   A Computerized Activated  Complex Model.   Proceedings
      of the  First World  Congress on Water Resources.   Chicago,
      Illinois,  4:284-294,  September 24-28,  1973.

(14)   Shaffer,  M. J.,  Dutt,  G. R.,  and Moore,  W.  J.,  Predicting Changes
      in Nitrogenous  Compounds in Soil-Water Systems,   Collected Papers
      Regarding Nitrates  in Agricultural  Waste Water.   U.S.  Government
      Printing  Office,  Washington,  D.C.,  1969.   p.  15-28.

(15)   Stockton,  J. C.  and Warrick,  A. W.,  Spatial Variability of
      Unsaturated Hydraulic Conductivity.   SSSAP, 35:847-848,  1971.

(16)   Dutt, G.  R., Effect of Small  Amounts of  Gypsum in Soils  on the
      Solutes of Effluents.   SSSAP.   28:754-757.   1964.

(17)   Dutt, G.  R., Prediction of the Concentration  of Solutes  in Soil
      Solutions  for Soil  Systems Containing Gypsum  and Exchangeable Ca
      and Mg.  SSSAP.   26:341-343.   1962.

(18)   Dutt, G.  R., and  Anderson, W.  D., Effect  of Ca-Saturated Soils
      on the  Conductance  and Activity of  Cl  ,  50. = ,  and Ca'1"''.   Soil
      Science.   98:   377-382.  1964.

(19)   Dutt, G.  R. and  Donneen, L. D., Predicting the Solute  Composition
      of the  Saturation Extract  from Soil  Undergoing Salinization.
      SSSAP.  27: 627-630.   1963.

(20)   Dutt, G.  R. and  Tanji, K.  K.,  Predicting Concentrations  of Solutes
      in Water  Percolated Through a Column of  Soil.   Jr. Geophys.  Res.
      69:3437-3493.   1962.

(21)   Dutt, G.  R., Terkeltoub, R. W., and  Ranschkolb,  R. S.,  Prediction
      of Gypsum and  Leaching Requirements  for  Sodium Affected Soils.
      Soil Science.   114:93-103.  1972.
                                226

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(22)  Hanks, R. J. and Bowers, S. A., Numerical Solution of the Moisture
      Flow Equation for Infiltration Into Layered Soils   SSSAP
      26:530-534.  1962.

(23)  Campbell, G. S.  "A Simple Method for Determining Unsatarated
      Conductivity from Moisture Retention Data," Soil Science
      Vol.  117, No. 6, pp.  311-314.  1974.

(24)  Hillel,  D.  "Soil and  Water, Physical Principles and Processes  "
      Academic Press,  New York, 1971, pp. 288.                     '
                                 227

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                             APPENDIX
The source code and sample output for the detailed model described
in this volume is available on microfische at cost from the authors,

Your request should be directed to:

             Dr. Marvin J. Shaffer
             Soil Scientist
             United States Department of Interior
             Bureau of Reclamation
             Engineering and Research Center
             P. 0. Box 25007
             Denver Federal Center, Building 67
             Denver, Colorado  80225
                                228

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                                    TECHNICAL REPORT DATA
                             (Please read Instructions on the reverse before completing)
  REPORT NO.
  EPA-600/2-77-179e
   2.
                                 3. RECIPIENT'S ACCESSIOf*NO,
4. TITLE AND SUBTITLE
                                                            5. REPORT DATE
 PREDICTION OF MINERAL QUALITY OF IRRIGATION RETURN
 FLOW, VOLUME V, Detailed Return Flow  Salinity and
 and) Nutrient Simulation  Model
                                  August  1977 issuing date
                                 6. PERFORMING ORGANIZATION CODE
7."AUTHOR(S)
 Marvin J.  Shaffer,  Richard W. Ribbens
 Charles W. Huntley
                                 8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
 Bureau  of Reclamation
 Engineering and Research Center
 Denver,  Colorado  80225
                                 10. PROGRAM ELEMENT NO.

                                     1HB617
                                 11. CONTRACT/GRANT NO.

                                     EPA-IAG-D4-0371
 12. SPONSORING AGENCY NAME AND ADDRESS
 Robert  S.  Kerr Environmental Research  Lab.
 Office  of Research  and Development
 U.S.  Environmental  Protection Agency
 Ada,  Oklahoma  74820
                     Ada,  OK
13. TYPE OF REPORT AND PERIOD COVERED
    Final
                                 14. SPONSORING AGENCY CODE
                                     EPA/600/15
 15. SUPPLEMENTARY NOTES
 VOLUMES I, II, III,  IV
(EPA-600/2-77-179a  thru 179d)
 16. ABSTRACT

  The  development  and evaluation of modeling capability to simulate  and predict the
  effects of irrigation on the quality  of return flows are documented in the five
  volumes of this  report.   The report contains two different modeling packages which
  represent different levels of detail  and sophistication.  Volumes  I, II,  and IV
  pertain to the model package given in Volume III.  Volume V contains the  more
  sophisticated model.   User's manuals  are included in Volumes  III and V.
17.
                                 KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                               b.lDENTIFIERS/OPEN ENDED TERMS
                                                                            COS AT I Field/Group
 Mathematical Model,  digital simulation,
 scheduling, Irrigated land, Evapotrans-
 piration, Agriculture,  Agronomy, Water
 pollution, Water  loss.
                     Irrigation Return Flow
                                                                               02 C/D
 3. DISTRIBUTION STATEMENT
 RELEASE TO PUBLIC
                     Unclassified
                                                      243
                                               20. SECURITY CLASS (This page)
                                                Unclassified
                                                                          22. PRICE
EPA Form 2220-1 (9-73)
                                              229
                                    A U.S. GOVERNMENT PRINTING OFFICE: 1977- 757-056/6550

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