&EPA
United States
Environmental Protection
Agency
Region 3
1860 Lincoln Street
Denver, Colorado 80295
EPA-908/3-78-002
August 1978
Water
Pollution Control Manual For
Irrigated Agriculture
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EPA-908/3-78-002
POLLUTION CONTROL MANUAL
FOR IRRIGATED AGRICULTURE
Prepared by
Keith Kepler, P.E., Project Manager
Don Carlson, Project Engineer
W. Tom Pitts, P.E., Program Manager
Toups Corporation
1966 West 15th Street
Loveland, Colorado 80537
Project Officer
Mr. George Collins
Contract No. 68-01-3562
August 1978
Prepared for
United States Environmental Protection Agency
Region VIII
Denver, Colorado
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This report has been reviewed by Region VIII, U.S. Environmental
Protection Agency and approved for publication. Approval does
not signify endorsement or recommendation for use by the U.S.
Environmental Protection Agency.
This document is available to the public through the National
Technical Information Service, Springfield, Virginia 22151.
Cover photo courtesy of Soil Conservation Service, U. S. Department
of Agriculture, Denver, Colorado.
11
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TABLE OF CONTENTS
1.0 INTRODUCTION 1
1.1 PURPOSE AND OBJECTIVES 1
1.1.1 The Federal Water Pollution Control
Act and Irrigated Agriculture .... 2
1.2 PROBLEM STATEMENT 3
1.3 HOW TO USE THIS MANUAL 4
1.4 IRRIGATED AGRICULTURE AND ASSOCIATED POLLU-
TION PROBLEMS IN THE UNITED STATES. 5
2.0 EVALUATION OF IRRIGATED AGRICULTURE AS A
POLLUTANT SOURCE WITHIN THE REGlOTTTiOTaTTSXT. . 26
2.1 THE PLANNING PROCESS 26
2.2 STUDY AREA INVENTORY 27
2.2.1 Water Sources and Delivery Systems. . 29
2.2.2 Water Quality and Quantity
Information 32
2.2.3 Irrigation Methods 33
2.2.4 Drainage Methods 35
2.2.5 Irrigated Areas 35
2.2.6 Climatic Conditions 36
2.2.7 Soils Data , . 36
2.2.8 Geologic Data 36
2.2.9 Chemical Use. . . 37
2.3 PROBLEM DEFINITION 37
3.0 DEFINITION OF BEST MANAGEMENT PRACTICES FOR
IRRIGATED AGRICULTURE .."".... 39
3.1 SUB-REGIONAL VS. ON-FARM EVALUATION 41
3.2 DEFINITION OF POLLUTANT PATHWAYS 42
3.3 CONTROL OPTION EFFECTIVENESS EVALUATION ... 48
3.3.1 Control Option Effectiveness
Determination 49
3.3.2 Effectiveness in Meeting Regional
Goals 52
ill
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TABLE OF CONTENTS (CONT.)
3.3.3 Determination of Sub-Regional Best
Management Practices 53
3.3.4 Estimation of Reduction in Pollutant
Loading 53
3.3.5 Determination of On-Farm Best Manage-
ment Practices 55
3.4 CASE STUDY - BEST MANAGEMENT PRACTICES FOR
IRRIGATED AGRICULTURE IN THE LARIMER-WELD
REGION OF COLORADO 56
3.4.1 Water Quality Impacts of Irrigated
Agriculture 56
3.4.2 Best Management Practices - Pollutant
Loading Mechanisms 58
3.4.3 Cost Effectiveness for BMP's in
Larimer-Weld Region 60
3'. 4.4 Conclusion 73
4 . 0 POLLUTANTS ASSOCIATED WITH JERRIGATION RETURN
FLOW AND THEIR EFFECTS UPONTgENETTcTAL USE.". 77
4.1 SOURCES AND LOADING MECHANISMS FOR POLLUTANTS
EMANATING FROM IRRIGATED AGRICULTURE 78
4.1.1 Salinity 78
4.1.2 Sediment 83
4.1.3 Nitrogen 84
4.1.4 Phosphorus 87
4.1.5 Pesticides 90
4.1.6 Other Pollutants 92
4.2 IDENTIFICATION OF WATER QUALITY PROBLEMS
ASSOCIATED WITH IRRIGATED AGRICULTURE .... 93
4.2.1 Locating Return Flows 93
4.2.2 Determination of Return Flow Quality
and Quantity 95
4.2.3 Analysis of the Water Quality Impacts
of Irrigation Returns 100
4.3 WATER QUALITY REQUIREMENTS FOR BENEFICIAL
USES 104
4.3.1 Irrigation Water 105
4.3.2 Livestock Water 109
4.3.3 Domestic Use Ill
iv
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TABLE OF CONTENTS (CONT.)
4.3.4 Fisheries 114
4.3.5 Recreation 115
5.0 IRRIGATED AGRICULTURAL PRACTICES AND POLLU-
TION CONTROL OPTIONS 116
5.1 DELIVERY SYSTEMS 116
5.1.1 Conveyance Systems 116
5.1.2 Flow Measurement 118
5.2 IRRIGATION APPLICATION SYSTEMS - DESCRIPTION.118
5.2.1 Furrow Irrigation 119
5.2.2 Border Strip Flooding 124
5.2.3 Level Basin Flooding 124
5.2.4 Wild Flooding 125
5.2.5 Sprinkler Irrigation 125
5.2.6 Drip Irrigation 126
5.2.7 Sub-Surface Irrigation 127
5.3 IRRIGATION APPLICATION SYSTEMS - COMPARISON
OF RETURN FLOW CHARACTERISTICS 127
5.3.1 Furrow Irrigation 127
5.3.2 Border Irrigation 135
5.3.3 Level Basin Irrigation 136
5.3.4 Wild Flooding 136
5.3.5 Sprinkler Irrigation 138
5.3.6 Drip Irrigation 138
5.4 IRRIGATION MANAGEMENT AND EFFICIENCY 138
5.4.1 Irrigation Management 138
5.4.2 Scientific Irrigation Scheduling. . .139
5.5 EXCESS WATER REMOVAL SYSTEMS 146
5.5.1 Tailwater Systems 146
5.5.2 Drainage 150
5.6 SOIL CONSERVATION PRACTICES ........ .150
5.7 FERTILIZER RESOURCE MANAGEMENT 152
5.8 EFFECTIVENESS AND COST OF POLLUTION CONTROL .153
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TABLE OF CONTENTS (CONT.)
5.8.1 Salinity 154
5.8.2 Nitrates 154
5.8.3 Sediment , 154
5.8.4 Other Pollutants Associated with
Surface Runoff :, 160
5.8.5 Costs of Irrigated Agricultural
Practices 160
6,'0 WATER LAW 162
6,1 WATER QUALITY LAW 162
6.2 WATER ALLOCATION LAW 163
6,2,1 Riparian Doctrine 165
6,2.2 Doctrine of Prior Appropriation . . .166
6.2.3 Ground Water Control Systems. . . , .168
6,2.4 Related Law 169
6.3 EFFECTS ON BEST MANAGEMENT PRACTICES 172
6.3.1 Water Quality Law: Issues. 172
6,3.2 Water Quantity Law Issues 173
APPENDIX A - REFERENCES 176
APPENDIX B - GLOSSARY 194
APPENDIX C - PESTICIDES 199
APPENDIX D - CONVERSIONS AND .CALCULATIONS 212
VI
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LIST OF FIGURES
Fig.
# Figure Title Page
1-1 Irrigated Land, 1969 7
1-2 Hydrologic Divisions 9
1-3 Irrigated Areas, Great Basin 11
1-4 Irrigated Areas, Upper Colorado River Sub-
Basin , . . . 13
1-5 Irrigated Areas, Lower Colorado River Sub-
Basin 15
1-6 Irrigated Areas, Arkansas-Red River Basin , . 17
1-7 Irrigated Areas, Rio Grande and Western Gulf
Region, „....,..,.,.., 19
1-8 Irrigated Areas, Missouri River Basin . . . . 21
1-9 Irrigated Areas, South Pacific Region .... 23
1-10 Irrigated and Potentially Irrigable Areas,
Pacific Northwest Region , . , , 25
2-1 BMP Manual Methodology - Identification of
Water Quality Impacts of Irrigation Return
Flow .............. 28
3-1 BMP Manual Methodology - Definition of Best
Management Practices. .... 40
3-2 Major Pollutant Pathways 43
3-3 Examples of Interrelationships 46
4-1 Water and Salt Balance. 82
4-2 The Nitrogen Cycle. 85
4-3 Pathways of Fertilizer Phosphorus ...... 88
4-4 The Phosphorus Cycle in Agriculture 89
4-5 Pesticide Cycling in the Environment 91
4-6 Irrigated Agriculture Return Flows. ..... 96
vii
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LIST OF FIGURES (CONT.)
Fig.
# Figure Title Page
4-7 Correlation of Mapped Data 102
4-8 Water Quality Analysis 103
4-9 Diagram for the Classification of Irrigation
Waters 106
5-1 Irrigation Methods 120
5-2 Advance Recession Curves for Surface
Irrigation 131
5-3 Surface Irrigation Soil Profile 132
5-4 Data Showing Relationship Between Irrigation
Efficiency and Water Cost 140
5-5 Pond Length Required for Quartz Particles to
Settle One Foot at Various Forward Velocities,
Using Stokes Law 149
6-1 Surface Water Law Systems in the Western
States 164
6-2 Ground Water Law Systems in the Western
States 170
Vlll
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LIST OF TABLES
Table
# Table Title Page
1-1 20 Leading States by Number of Irrigated
Acres: 1974 6
1-2 Distribution of Irrigated Land by
Major Basin , 5
2-1 Sources of Information 30
2-2 Kinds of Information 31
3-1 Summary of Factors Contributing to
Pollutant Loading 44
3-2 Loading Mechanisms for Pollutants Associated
With Irrigation Return Flow 45
3-3 Control Option Effectiveness Comparison -
Example: Salinity 51
3-4 Ranking of Sub-Basin Alternatives and
Cost Estimation 54
3-5 Pollutants Affected by BMP' s 62
3-6 Loading-Reduction Effectiveness Factors 64
3-7 Capital Costs of BMP's 67
3-8 Annual Costs Per Acre 68
3-9 Annual Costs 70
3-10 Benefits Per Acre 71
3-11 Comparison of Effectiveness to Net Cost -
Salinity 74
3-12 Comparison of Effectiveness to Net Cost -
Nitrates 75
3-13 Comparison of Effectiveness to Net Cost -
Sediment 76
4-1 Suitability of Waters for Irrigation 107
4-2 Relative Salt Tolerance of Various Crop
Plants 108
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LIST OF TABLES (CONT.|
Table
# Table Title Page
4-3 Guide to the Use of Saline Waters for
Livestock and Poultry 110
4-4 EPA Water Quality Standards for Discharge
to Ground Waters Utilized as a Drinking
Water Supply 112
5-1 Suitability of Irrigation Methods 128
5-2 Typical Return Flow Characterisitcs of
Irrigation Methods 129
5-3 Concave Slope Results on Borders 137
5-4 Estimated Reduction in Pollutant Loading
for Various Control Options as Compared to
Furrow Irrigation .... .155
5-5 Average Water Losses to Deep Seepage for
Irrigation Systems ,157
5-6 Expected Sediment Loss Reduction for Selected
Control Practices on Typical Irrigated Farms
in the Magic Valley and Boise Valley 159
6-1 Characteristics of Water Rights in Western
States 171
x
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CHAPTER 1 INTRODUCTION
1.1 PURPOSE AND OBJECTIVES
Current interest in controlling the pollution load from
irrigated agriculture has been brought about by:
o The Federal Water Pollution Control Act;
o The international agreement between the
U.S. and Mexico concerning salinity
levels in the Colorado River;
o Several significant regional and local
problems where salts have reduced crop
yield, nutrients have contributed to eutrophi-
cation of lakes or bays, or sediment has
impaired water quality.
Understanding of the relationships between irrigated
agriculture and water quality has been concentrated in a
relatively small group at the research level. This manual
is intended to expand understanding of irrigated agriculture-
water quality relationships to a much broader group,
including:
o Water quality planners and agencies;
o Water resource planners and agencies;
o Agricultural field technicians.
In order to do this, the manual presents:
o A brief look at irrigated agriculture in the
Western United States, and the associated
pollution problems;
o A methodology for evaluating the water
quality impacts of irrigated agriculture
within a region;
o A methodology for evaluating potential
best management practices within the
context of regional problems and regional
goals;
o A discussion of the pollutants associated with
irrigation return flow, their loading
mechanisms, and effects upon beneficial use;
o A review of irrigated agricultural practices
and associated pollutant loading mechanisms;
o A brief discussion of water law.
The presentation of technical information on pollutants,
irrigation practices, and water law is not intended to
be inclusive of all current knowledge and data. Rather,
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it is intended as background material for those who
may not be directly engaged in irrigation return flow
pollution control technology. In this way, it is hoped
that the agriculturalist can develop an understanding of
pollution aspects of irrigation and that water quality
interests will develop an understanding of irrigated
agriculture and the limitations of a stream imposed by
irrigation water requirements.
1.1.1 The Federal Water Pollution Control Act and
Irrigated Agriculture
1977 Amendments to the Federal Water Pollution Control
Act (P.L. 92-500) have resulted in significant changes
in the way irrigated agriculture is to be addressed.
Provisions in Section 208 require that an areawide
waste treatment management plan prepared under
such process shall include:
"a process to identify, if appropriate,
agriculturally and silviculturally related
nonpoint sources of pollution, including return
flows from irrigated agriculture and their
cumulative effects, runoff from manure disposal
areas, and from land use for livestock and crop
production, and set forth procedures and
methods including land use requirements to
control to the extent feasible such sources;"
Section 208, (b) (2) (F)
These amendments also provide for a method of achieving
best management practices. Public Law 92-500, Section 208,
paragraph (j)(l) states:
"The Secretary of Agriculture, with the
concurrence of the Administrator, and acting
through the Soil Conservation Service and
other agencies...is authorized and directed to
establish and administer a program to enter
into contracts...for the purpose of installing
and maintaining measures incorporating best
management to control nonpoint source pollu-
tion for improved water quality in those
States or areas for which the Administrator
has approved a [208]plan..."
The Amendment goes on to explain administration of the
document and to allow for funding to become available
in Fiscal Year 1979.
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The basic requirements for funding of nonpoint source
best management practices as stated in Section 208
are then:
o A 208 Plan including a process to identify
nonpoint sources including irrigated
agriculture;
o A 208 Plan which sets forth procedures and
methods to control nonpoint sources
(Section 208, (b)(2)(F).
This manual focuses on development of information necessary
to fulfill these requirements including:
o Identification of water quality problems
associated with irrigated agriculture and
identification of problem areas;
o Definition of best management practices
within the local context.
The manual is intended to aid local areas in achieving
these requirements. Through development of sound pro-
grams, funds provided under the 1977 Amendments can become
available to 208 agencies and can be used effectively.
1.2 PROBLEM STATEMENT
Problems involved in the definition of water quality
problems associated with irrigation returns, definition
of best management practices, and implementation of best
management practices are many. These problems include:
o Lack of data on the quality of returns in
many areas;
o Lack of perspective on agricultural water
problems in many basin plans;
o Methodology for data collection and
evaluation of water quality problems
in irrigated areas has not been
adequately brought forth;
o In many instances, technology is
yet developing. Utilization of soils
data in water quality studies is one
such area;
o Designated 208 areas often have an urban
base; as a result, emphasis may have been
directed towards urban problems;
o Prediction of results obtained through
implementation of best management
practices cannot be conducted with a high
degree of accuracy under current technology;
monitoring results is equally difficult;
o The major water quality problem associated
with irrigation in the West is salinity -
for the mosi part this is the inevitable
result of consumptive use. As a result,
best management practices for irrigation
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can only hope to reduce that small portion
of salt concentrations due to non-beneficial
or excessive consumptive use. Natural
salt sources and saline soils contribute to
salt load in a few areas, both irrigated and
non-irrigated, but these are also quite
difficult to control.
1.3 HOW TO USE THE MANUAL
This manual is intended to give an overview of the tech-
nology involved in evaluating and reducing pollutants
associated with irrigation return flow and to provide a
methodology which can tie the technical steps into a
planning process.
In order to do this, the manual has been divided into
six chapters!:
Chapter 1
Chapter 2
Chapter 3
Chapter 4
Chapter 5
Chapter 6
Introduction
Evaluation of Irrigated
Agriculture as a Pollutant
Source Within the Regional Context
Definition of Best Management
Practices for Irrigated Agri-
culture
Pollutants Associated with Irrigated
Agriculture and Their Effects Upon
Beneficial Uses
Irrigated Agriculture Practices
and Pollution- Control Options
Water Law
Chapters 2 and 3 present a methodology for evaluation of
water quality impacts resulting from returns and evalua-
tion of best management practices. These chapters form
the center of this report. While each area will require
a methodology adapted to its own needs, the basic steps
are not expected to vary significantly from those
shown in Figures 2-1 and 3-1.
Chapters 4 and 5 provide background technical infor-
mation. Chapter 6 provides a brief introduction to water
law aspects of irrigated agricultural pollution control.
This information has been presented in a manner which
should make it widely available. More detailed informa-
tion can be gained from the references.
Efficient use of nonpoint source control dollars requires
educated agricultural field personnel, and it is hoped
that this manual will serve the Soil Conservation Service
and other agencies in this capacity.
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The methodology has been developed primarily through
the consultant's experience in northern Colorado. In
this area, 208 work has included not only a technical
definition of problems and best management practices,
but also a social-institutional study. Institutional
assignments have been made concerning planning, manage-
ment, operations, and enforcement. Current work is being
focused on the assignment of specific tasks to the
agencies which will soon have implementation respon-
sibilities.
1.4 IRRIGATED AGRICULTURE AND ASSOCIATED POLLUTION
PROBLEMS IN THE UNITED STATES
A combination of social, economic, and physical
factors determine the feasibility of crop irrigation.
Social and economic factors demand intensified and
stable crop production. Physical factors determine both
the need for and feasibility of crop irrigation in an
area. More than 90 percent of the total acreage irri-
gated on all farms in the nation are located in the
17 western states and Louisiana. Table 1-1 displays
a breakdown of irrigated acreages in the twenty
leading irrigation states. Figure 1-1 shows irrigated
areas in the United States.
Irrigated land in the western states is distributed in
eight major river basins (Figure 1-2). Table 1-2
shows the distribution of irrigated land within these
basins.
TABLE 1-2. DISTRIBUTION OF IRRIGATED LAND BY
MAJOR BASIN
APPROXIMATE
IRRIGATED
LAND
REGION (million acres)
Great Basin 1.6
Colorado
Upper Colorado
Lower Colorado
Arkansas Red River
Rio Grande - Western Gulf
Missouri
South Pacific
Pacific Northwest
TOTAL 37.3
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TABLE 1-1 20 LEADING STATES BY NUMBER OF
IRRIGATED ACRES: 1974 (a) (b)
Rank
Irrigated
Acres (c)
Percent
of all
Irrigated
Acres
Change
Since
1969
+ or - %
(d)
United States
20 Leading
41,243,023
100
+ 3.1
States
1 California
2 Texas
3 Nebraska
4 Colorado
5 Idaho
6 Kansas
7 Montana
8 Oregon
9 Wyoming
10 Florida
11 Washington
12 Arizona
13 Utah
14 Arkansas
15 New Mexico
16 Nevada
17 Louisiana
18 Oklahoma
19 Mississippi
20 South Dakota
39,948,099
7,748,709
6,593,832
3,966,930
2,873,692
2,859,047
2,010,385
1,759,040
1,561,438
1,459,900
1,558,735
1,309,018
1,153,478
969,645
948,910
867,325
777,510
701,587
515,104
161,611
152,203
9.9
18.8
16
9.6
9.6
6.9
4.8
4.2
3.8
3.5
3.8
3.2
2.8
2.3
2.3
2.1
1.9
1.7
1.2
0.4
0.4
+ 5.0
+ 7.0
- 4.2
+ 49.0
- 0.7
+ 3.6
+ 32.0
- 4.3
+ 2.7
- 6.0
+ 14.0
+ 6.9
- 2.0
- 5.5
- 6.1
+ 5.5
+ 3.3
0
- 1.7
+ 7.8
+ 2.7
(a) All Farms.
(b) U.S. Department of Commerce, 1974, Census of Agriculture,
(c) Hectares = .4047 x acres.
(d) U.S. Department of Commerce, 1969, Census of Agriculture,
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IN EASTERN U.S., ONE DOT ( -) EQUALS 10.000
ACRES. C USDC , 1973 3
IRRIGATED LAND
FIGURE 1-1. IRRIGATED LAND, 1969 (A)
(A) 1969 Census of Agriculture
TOUPS CORPORATION
Loveland, Colorado
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The pollutants most commonly associated with irri-
gated agriculture in these basins are salinity,
sediment, and nutrients. Concern for other specific
constituents associated with irrigated agriculture
may increase in the future as new environmental
legislation is passed and more stringent water
quality standards are enacted to meet environmental
goals.
The significance of pollutant discharge in irrigated
agriculture is dependent upon a number of factors
including the availability of in-stream water for
dilution of return flows and beneficial uses at the
point of discharge and downstream. The impact of
irrigation return flows varies considerably among
basins and within basins. Analysis of water quality
impacts of irrigated agriculture is often complicated
by discharge of the same pollutants from natural
sources.
The remaining sections of this chapter provide a
description of agricultural practices within the
basins shown in Figure 1-2. Included in these
descriptions are the following items:
o Irrigated acreage;
o Climate and crops;
o Irrigation and drainage practices;
o Water supply;
o Water quality.
These descriptions are intended to provide a brief
synopsis of characteristics of irrigated agricultural
practices within the eight regions.
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vO
PACIFIC NORT
BASIN__
GREAT BA^IN
( \
SOUTH
PACIFIC
LORW10-4--
RIVER '
BASIN
ARKANSAS-RED RIVER
1 ! BASIN
-RJQ-fi(RANDE AND
WESTERWNGULF REGION
\
FIG. 1-2. HYDROLOGIC DIVISIONS [A]
USGS, I966
toups
corporation
loveland, co.
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GREAT BASIN
Irrigated Acreage; Approximately 1.6 million acres (a)
Climate and Crops: Highly variable depending on elevation
and latitude. Major irrigated areas have a growing season
from 100-175 days, placing some limitations on crop types.
Close grown crops (primarily alfalfa, hay, and small grains)
are utilized on about 70 percent of the irrigated land, and
approximately 24 percent is in pasture(b).
Irrigation and Drainage Practices;
Irrigation Method Percent of Irrigated Acreage
Sprinklers 8
Furrows or Ditches 30
Flooding 61
Subirrigation 1
The predominance of close growing crops is reflected in
the high percentage of flood irrigation. Drainage is
required in many areas with 14 percent of the irrigated
land utilizing drainage facilities.
Water Supply; Surface water is by far the major source of
supply.The Great Basin area is a combination of several
closed basins. Since surface water is the major supply
source, water use is commensurate with supply.
Water Quality; Salinity appears to be the major regional
water quality problem. Both natural sources and irrigation
return flow contribute to this problem. Limited water
resources result in the reuse of most return flows. This
system of reuse results in only a minimal volume of highly-
mineralized returns. Return flows typically follow streams
to dead lakes of which the Great Salt Lake is an example.
These dead lakes must be considered to be nutrient sinks,
since nutrient outflow pathways are minimal. Actual nutrient
problems are largely undocumented, however. The predominance
of close growing crops indicates that nutrient (fertilizer)
use and nutrient loss may be low.
(a) 1969 Census of Agriculture data modified to incorporate
changes indicated by the 1974 census.
10
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-^ ^FJv,
f -•../• *'".=: '••>
FIGURE 1-3. IRRIGATED AREAS, GREAT BASIN
11
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UPPER COLORADO RIVER BASIN
Irrigated Acreage; Approximately 1.45 million acres(a)
Climate and Crops; Climate is widely varying depending upon
elevation and latitude. A wide variety of crops are grown,
although some climatic restrictions exist throughout the
Upper Colorado area.
Irrigation and Drainage Methods;
Irrigation Method Percent of Irrigated Acreage(a)
Sprinklers 4
Furrows or Ditches 49
Flooding 46
Subirrigation 1
The fact that surface waters provide the primary source
results in only a very small percentage of sprinkler irrigation,
Water Supply; Surface waters provide nearly all supply
water for irrigation use in the Upper Colorado River Basin.
Mountain runoff supplies the bulk of this water, with only
minimal runoff from the desert which occurs at lower eleva-
tions. Approximately 37 percent of irrigated lands receive
less than an adequate water supply(b).
Water Quality; Salinity has been a topic of major concern
in the Colorado River Basin. -Within the Upper Colorado
Basin, many of the problems are the result of natural springs
and surface runoff. Approximately 37 percent of the total
salt load at Lee Ferry has been attributed to irrigation,
with most of the rest attributal to natural sources. The
geology of the area is the primary complication, both for
the irrigated and natural salt load. Average TDS concen-
tration at Lee Ferry is 586 mg/l(b).
(a) 1969 Census of Agriculture data modified to incorporate
changes indicated by the 1974 census.
(b) Toups Corporation, 1975.
12
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v •?«* ]• f--.\
-- •-/ •;•."«/ ./
rOLQ"* DO J [f tf^ * * /
FIG. 1-4. IRRIGATED AREAS, UPPER COLORADO
RIVER SUB-BASIN
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LOWER COLORADO BASIN
Irrigated Acreage: Approximately 1.24 million acres(a)
Climate and Crops; Most of the irrigated area lies in
southern Arizona. In this area, the warm climate allows a
wide variety of crops and high productivity.
Irrigation and Drainage Methods;
Irrigation Method Percent of Irrigated Acreage(a)
Sprinkler 4
Furrow or Ditch 70
Flooding 26
Approximately 13 percent of the irrigated land is drained.
Water Supply: There are two major irrigated areas within
what we are considering to be the Lower Colorado River Basin.
The Central Arizona Area is primarily served by ground water.
206,000 acres are served by surface water, but they have
supplemental ground water available, and 575,000 acres are
supplied by ground water alone(b)
Ground water in the Central Arizona area is being mined, and
each year acreage is taken out of production as pumping levels
become deeper. Painted Rock Dam on the Gila River essen-
tially isolates this area from the lower Gila River and
from the Colorado River(b).
Irrigation water for the lower Colorado Basin, including the
Welton Mohawk Project, the Yuma Project, and Imperial Valley
in California are supplied by the Colorado River. While the
Upper Colorado River supplies 72 percent of the salt load
to this area, it should also be noted that it supplies 90
percent of the water.
Water Quality; Salinity is the major water quality problem
in the Lower Colorado Basin and is primarily the result of
high demand for a commodity in limited supply. Natural
sources play a significant part in the salt load as well.
Water entering the Lower Basin at Lee Ferry has an average
TDS of 586 mg/1, and water at Imperial Dam has an average
TDS of 839 mg/1. The use of all the good water and the
pumping of very poor quality drainage water has resulted in
an inability to supply Mexico with good water. Desalinization
is being planned to alleviate this problem at great expense(c)
Salinity is the major water quality problem in the Central
Arizona area. The salinity problem appears to be secondary
to the water supply problem except in localized areas,
however.
Ta)Census of Agriculture, 1969 and 1974.
(b) John Erickson.
(c) Toups Corporation 1975.
14
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FIG. 1-5. IRRIGATED AREAS, LOWER COLORADO
RIVER SUB-BASIN
15
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ARKANSAS-RED RIVER BASINS
Irrigated Acreage; Approximately 4.2 million acres(a)
Climate and Crops: In most of the irrigated portion of the
Basin, long hot summers and short, cold winters are the
rule. The climate becomes warmer, milder, and more humid
as one gets closer to the Gulf. A wide variety of crops
are grown ranging from corn, hay, small grain and truck
crops in the western portion to cotton and peanuts along
the Oklahoma-Texas border.
Irrigation and Drainage Methods:
Irrigation Method Percent of Irrigated Land(a)
Sprinkler 15
Furrow or Ditch 71
Flooding 14
Subirrigation less than 0.5
Nearly all the acreage irrigated by sprinklers lies on the
high plains. Approximately 5 percent of the irrigated land
is drained.
Water Supply; The Arkansas River and alluvium in Colorado
is fed primarily by mountain runoff, with some contributing
local runoff. Irrigation on the high plains is fed by
the Ogallala aquifer which is being mined. Irrigation along
the Red River east of the Texas Panhandle is primarily
supplied by local runoff, alluvial wells, and local aquifers,
Water Quality: The Arkansas River is the most saline of
major rivers in the country as it enters Kansas. This has
been attributed to concentration of salts through reuse
(85 percent of the surface water supply is consumptively
used in Colorado) and natural salt pickup between Canon
City and Pueblo(b).
Irrigation on the high plains has little effect on surface
waters. Aquifer depletion presents a problem, however.
The Red River and Arkansas River and their tributaries
are all affected by natural brine emissions. Oil field
brine emissions also contribute to the salt load in some
areas.
(a) Census of Agriculture, 1969 with available 1974 data
incorporated.
(b) Miles, Don. Salinity in the Arkansas Valley of
Colorado, Colorado State University and U.S. EPA. 1977.
16
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FIG. 1-6. IRRIGATED AREAS, ARKANSAS
RED RIVER BASIN
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RIO GRANDE AND WESTERN GULF REGION
Irrigated Acreage; Approximately 6.2 million acres(a)
Climate and Crops: Widely varied depending upon elevation,
latitude, and proximity to the Gulf of Mexico.
Percent of Total Irrigated Acreage(a)
Row Crops 67
Close Grown Crops 24 (1)
Tree Crops 1
Irrigated Pasture 8
(1) Including rice (about 550,000 acres)
Irrigation Method;
Percent of Irrigated Acreage With
Irrigation Method This Method (a)
Sprinkler 18
Furrow or Ditch 59
Flooding 22
Subirrigation 1
Approximately 13 percent of the irrigated land is drained.
Water Supply; Surface and alluvial sources supply water
along the Rio Grande and Pecos Rivers. Ground water from
the Ogallala aquifer supplies water for irrigation on the
high plains. This water is being mined, and the water table
is lowered each year. Areas draining directly to the Gulf
are supplied by either surface or ground water.
Water Quality; The Pecos River has some of the worst problems
in the U.S. Irrigated agriculture contributes signifi-
cantly to salinity problems and to a lesser extent to sedi-
ment problems. High sediment loads are largely attributable
to runoff from grazing land. Natural salt sources are abun-
dant in the Pecos Basin. The extremely low rainfall is at the
root of many water quality problems.
The Rio Grande displays the effects of continued reuse of
waters for irrigation. TDS concentrations at El Paso vary
considerably with flows attributable to irrigation return
(winter) from 1,000-2,000 mg/1 and summer flows augmented by
reservoir releases in the 600-700 mg/1 range(b).
While high plains irrigation has little effect upon surface
water, depletion of the aquifer represents a significant
problem.
(a)Census of Agriculture 1969 and 1974.
(b) Toups Corporation 1975.
18
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4 III Ol M01MT mitt luir
FIG. 1-7. IRRIGATED AREAS, RIO GRANDE AND
WESTERN GULF REGION
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MISSOURI RIVER BASIN
Irrigated Acreage; Approximately 9 million irrigated acres(a)
Climate and Crops; The continental climate includes hot
summers and cold winters. The growing season is further com-
plicated by somewhat eratic spring weather in the northern
and western portions. Corn, hay, small grains, and sugar
beets are primary irrigated crops.
Irrigation and Drainage Methods;
Irrigation Practices
Irrigation Method Percent of Irrigated Acreage(a)
Sprinkler 21
Furrow and Ditches 52
Flooding 26
Subirrigation 1
Drainage Practices
Percent of Land Irrigated By
Irrigation Method This Method Which is Drained(a)
Sprinkler 2
Other Methods 10
Water Supply; The Missouri River Basin actually consists of
two major irrigation systems. Surface runoff from the Rockies
and the rest of the basin supplies water to irrigators along
rivers and alluvial areas. This system receives annual re-
charge. The second system, on- the high plains, overlies
the vast Ogallala aquifer. The Ogallala aquifer is being
drained of water with recharge insignificant compared to with-
drawal. Development of this aquifer has contributed to
increased irrigated acreage of 49 percent in Nebraska and
32 percent in Kansas from 1969 to 1974.
Water Quality: Salinity is the major problem in streams and
alluvium of irrigated portions of the Basin. Nutrient and
sediment problems are localized. The region is large and
data is lacking, partially because problems have not become
severe.
Irrigation on the high plains - much of it sprinkler - has
little effect on surface water quality. Depletion of the
deep Ogallala aquifer is a more serious problem than
pollution.
(a) 1969 Census of Agriculture Data altered to incorporate
available 1974 data.
20
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FIGURE 1-8. IRRIGATED AREAS, MISSOURI RIVER BASIN
-------
SOUTH PACIFIC REGION
Irrigated Acreage; 7.75 million acres(a)
Climate and Crops; Much of the area, especially along the
coast and in southern portions enjoys a long growing season
allowing production of most crops which are grown elsewhere,
plus several crops which cannot be grown elsewhere in the
continental United States.
Irrigation and Drainage Practices;
Irrigation Practices
Irrigation Method Percent of Total Irrigated Acreage(a)
Sprinklers 18
Furrow or Ditches 43
Flooding 38
Subirrigation 1
Drainage is required on much of the land with approximately
25 percent of the total irrigated acreage drained.
Water Supply: While northern California enjoys plentiful
water supply, southern California has problems in terms of
both water supply and supply water quality. Reuse of the
limited quantities results in significant mineral degrada-
tion of water in southern California (the San Joaquin Basin,
the Tulare Basin, and the Imperial Valley).
Agricultural water supply has undergone encroachment by urban
demands. Water importation has major significance in the
region.
Water Quality; Salinity is a water quality problem which
exists in both surface and ground waters throughout the
southern portions of the region. These portions are especially
acute in the Tulare Lake Basin and in the Salton Sea Basin
(b).
Nutrient loading from the Central Valley (Sacramento and San
Joaquin Rivers) is of concern since these rivers drain into
San Francisco Bay.
(a) Census of Agriculture, 1969 and 1974 data where available.
(b) Toups Corporation 1975.
22
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FIGURE 1-9. IRRIGATED AREAS, SOUTH PACIFIC REGION
23
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PACIFIC NORTHWEST
Irrigated Acreage: Approximately 5.75 million acres(a)
Climate: Range of frost-free days dependent upon elevation.
Crops; Irrigated crop types are as follows: (a)
Crop Type Percent of Total Acreage
Row Crops 16
Close Grown Crops 59
Tree 5
Irrigation Pasture 20
Irrigation and Drainage Practices:
Irrigation Practices (a)
Irrigation Method Percent of Total Irrigated Acres(a)
Sprinklers 34
Furrow or Ditches 38
Flooding 26
Subirrigation 2
Drainage Practices
Percent of Acreage Irrigated by This
Irrigation Method Method Which Are Drained(a)
Sprinklers 10
Other Methods 12
Water Supply; The Pacific Northwest has an ample supply of
water, but problems occur in time and place. Shortages of
water are noted in the eastern portion of the region, parti-
cularly the Upper Snake River Basin. Inadequate ground water
supply is noted in the Mid-Columbia and Upper'Columbia areas.
Water Quality: Sediment is the major pollutant problem in
the Northwest, and irrigation return flows are largely respon-
sible. Sediment problems are particularly significant in the
Snake and Yakima Rivers. Within the region, significant
research on combating problems has been conducted by the land
grant universities, U.S .D. A. -ARS, U.S. D. A. -SCS , and others.
Salinity is not an areawide problem. Salinity problems
appear to be confined to upper river reaches to the east
central portion of Washington and in closed basins. Sodium
and salinity problems occur in a few tributaries south of the
Snake River in Idaho.
Nutrient problems occur in several locations throughout the
region.
(a) Census of Agriculture 1969 and 1974 data.
24
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N3-
| | POTENTIALLY IRRIGABLE AREA
I^H PRESENTLY IRRIGATED AREA
FIG.1-10. IRRIGATED AND POTENTIALLY
IRRIGABLE AREAS, PACIFIC
NORTHWEST REGION
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2.0 EVALUATION OF IRRIGATED AGRICULTURE
AS A POLLUTANT SOURCE WITHIN THE REGIONAL CONTEXT
2.1 THE PLANNING PROCESS
The development of an understanding of the water quality
impacts of irrigation return flow represents the first
step in developing and applying best management practices,
Understanding of impacts in a local area is the basis
for assigning priorities for reducing pollution due to
return flow. Key elements of the planning process are
displayed in Figure 2-1.
In order to evaluate water quality problems relative to
irrigated agriculture/ a wide variety of information is
necessary. Although much information may be already
available for an area, additional information will be
required to address specific problems. Data can then be
analyzed to determine specific problem areas, water
quality problems, and the significance of irrigation
return flows in the make-up of regional water quality.
The manual methodology is dependent upon water quality
goals and regional priorities. Water quality problems
from irrigated agriculture may be associated with either
entire river basins or much smaller problem units due to
natural conditions or commonly used irrigation practices.
Some problems can be related specifically to individual
fields. For example, excess fertilizer application and
over irrigation could create a nitrate problem in the
return flow for a single field.
Understandably, one water quality problem may be caused
by one problem area, and another quality problem by
another area. For purposes of this evaluation, problem
areas can be divided as follows:
Sub-regional River basins
River sub-basins
Irrigation districts
Drainage districts
26
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On-farm Groups of adjacent farms
Individual farms
Individual fields
Areas within single fields
During the planning and program direction phase of an
evaluation process, a progression is made from "sub-
regional" areas to "on-farm" areas. However, implementation
steps often proceed from "on-farm" areas to "sub-
regional" areas.
While the solutions to water quality problems within
the suggested problem areas may be the most reasonable
and practicable, there may be prohibitive institutional
constraints. Political areas, defined by county or' state
boundaries, generally have adequate legal tools and
organizations to implement programs more easily than
geographical areas. Regional, statewide, and perhaps
joint-state 208 planning is an excellent mechanism for
developing solutions to agricultural pollution problems.
2.2 STUDY AREA INVENTORY
In order to analyze water quality problems and to recommend
best management practices, existing irrigation practices
and environmental conditions must be inventoried. Much
information is available but disposed among- various
disciplines:
Agriculture Land use
Hydrology Engineering
Geology Water quality
Biology Agronomy
Economics Atmospheric science
Law Environmental health
Soils Water resources
Chemistry Planning
Information within these areas relative to irrigation
return flow can be found at various levels of government
and in the private sector. Table 2-1 contains a list of
potential sources of information.
27
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EXISTING
PRACTICES
• ON FARM
• IRRIGATION OR
DRAINAGE
DISTRICT
D
FIXED
CONDITIONS
• SOILS
• GEOLOGY
• WATER SUPPLY
zmn
WATER QUALITY
INFORMATION
• EXISTING DATA
• DATA FROM
SAMPLING
RETURNS
13 CH
WATER QUALITY
GOALS
• BENEFICIAL USE
• STREAM
STANDARDS
REGIONAL a
SUBREGIONAL
WATER QUALITY
PROBLEMS
RESULTING
FROM
RETURN FLOWS
D
D
flr
D
Q
D
HT-*
y
REGIONAL a
SUBREGIONAL
PRIORITIES FOR
REDUCING
POLLUTION
DUE TO
RETURN FLOW
FIG 2-1. BMP MANUAL METHODOLOGY -
IDENTIFICATION OF WATER QUALITY IMPACTS OF
IRRIGATION RETURN FLOW
28
toups
corporation
loveland, co.
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In addition, the data should be collected at two
levels: on-farm and sub-regional. Table 2-2 lists
the types of information necessary for both levels.
Generally speaking, on-farm data is much more specific
and detailed than sub-regional data. The same type
of information may be necessary at both levels, but in
different degrees of detail.
Information relative to on-farm conditions and practices
is available primarily through consultation with farmers
themselves. The local Soil Conservation Service office
can provide basic soils information. Flow data and water
quality data will probably have to be collected by
trained technicians and chemists, since farmers usually
do not collect this information.
Sub-regional information will be found in practically
each source listed in Table 2-1. Familiarity with the
study area will indicate which are primary sources and
which are secondary sources. The size of the study area
and required detail will determine the sources.
2.2.1 Water Sources and Delivery Systems
Sources of irrigation water include groundwater and
surface water. Locations and yields of wells and ground-
water levels can be obtained from the U.S. Geoligical
Survey (USGS) or state geological surveys. State agencies
responsible for groundwater rights administration may have
records of more recent wells.
The U.S. Bureau of Reclamation (USSR) supplies surface
water to many areas and has records of deliveries from
their projects.
Irrigation districts and conservancy districts have records
available regarding storage, reservoir locations,
capacities, etc. Locations and capacities of canals are
also available. Many canal locations are indicated on USGS
quad maps. State engineers' offices or state water
resource agencies have additional information.
29
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TABLE 2-1. SOURCES OF INFORMATION
Soil Conservation Service
Cooperative Extension Service
College Experiment Stations
Vocational Agricultural Service
U.S. Geological Survey
Equipment Dealers
Consulting Engineers
State Water Resource Agencies
State Water Quality Agencies
County Planning
Environmental Protection Agency
U.S. Department of Agriculture
State Departments of Agriculture
Regional Governmental Agencies
U.S. Department of Commerce (Census)
Agriculture Supply Dealers
National Weather Service
U.S. Bureau of Reclamation
County Health Departments
Farmers
Libraries
Irrigation Districts
County Agents
Universities
Farm Magazines
River Commissioners
State Water Research Institute (Land Grant College)
U.S. Corps of Engineers
Ditch Riders and Local Watermasters
Consulting Irrigation Engineers
30
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TABLE 2-2. KINDS OF INFORMATION
On-Farm
Application method
Drainage system
Soil types
Soil intake rates
Field slopes
Labor costs
Crops
Field shape
Water quality
Return flow
Fertilizer use
Pesticide use
Maintenance costs
Water rights
Flow data
Sub-Regional
Climate
Topography
Irrigation districts
Conveyance systems
Geology
Hydrology
Storage reservoirs
Aquifers
Maintenance costs
Drainge
Return flow
Water quality
Water quantity
Water rights
31
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Irrigation districts and local ditch companies have
cost data for construction and maintenance of reservoirs
and canals. Miles of lined and unlined canals, flow
measurement methods, irrigated acreages, plus delivery
times and seasons, can also be obtained.
2.2.2 Water Quality and Quantity Information
Stream flow and water quality records are maintained by
the U.S. Geological Survey as well as several other
Federal and State agencies. Existing flow and quality
data may well be the best source available in pinpointing
irrigation return flow problems in an area. While it
may provide a basis for problem identification, a more
in-depth study leading to definition of specific local
problems may require on-site sampling and flow
measurement.
Most of the stations maintained by the USGS and other
agencies have rather long periods of record and may be
used to obtain information on averages and trends.
Existing data can also provide an insight to the impact
of irrigation return flows, but it cannot be substituted
for an understanding of the conditions which bring
about these changes in water quality and quantity.
Records for the major stations are published annually
in the USGS publication Water Resources Data for (State)
which is published in two parts—Part I, Surface Water
Records, and Part II, Water Quality Records. Collection
of this data is probably a first step in analyzing an area,
The Catalog of Information on Water Data, published by
the U.S. Department of Interior, Geological Survey, Office
of Water Data Coordination, contains a listing of all
water data stations maintained by the USGS and other
Federal and State agencies. This publication can be used
to identify all data stations and their periods of record,
32
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as well as the types of data offered. The actual
data is not included and must be found elsewhere.
The catalog contains several volumes divided into
river basins. It is available from: Office of
Water Data Coordination, U.S. Geological Survey,
National Center, Mail Stop 417, Reston, Virginia
22092.
STORET is another such water quality data file,
maintained by the U.S. Environmental Protection Agency.
Printouts of the data can be obtained through the EPA.
USGS and EPA water quality records are generally for
larger streams and rivers in a state. State water
quality agencies have on-going monitoring programs in
most states. Some local agencies such as county health
departments and designated 208 agencies also have
water quality data.
The EPA and State water quality agencies have Section 303,
Section 208, and Section 201 documents. These documents
are Regional Water Quality Plans, Areawide Waste
Treatment Plans, and Waste Treatment Facility Plans,
respectively. Many of these plans have good water quality
information.
2.2.3 Irrigation Methods
General knowledge of irrigation methods is necessary in
evaluating problems associated with irrigation return
flow. While statistics can be obtained from the U.S.
Department of Commerce, Census of Agriculture, and from
the various state departments of agriculture, these
statistics are generally on a county-wide basis. Such
statistics are useful in presenting general background
information on an area, but do not give sufficient detail.
33
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Local agricultural experts including extension per-
sonnel and Soil Conservation Service personnel are
the best source of information regarding the
irrigation methods predominately used within a
region. When gathering information about irrigation
systems, several items are important:
Type of system
Slopes of fields
Water application rates
Water intake rates of soils
Shapes of fields
Description of crops (consumptive use of water)
Labor required (hours per acre per irrigation)
Costs of system (capital, operation, and
maintenance)
Adaptable to fertilizer and pesticide use
Irrigation season and scheduling
Irrigation costs which include capital costs, and
operation and maintenance costs, are important to the
irrigator if he is to change his system or adopt a new
one. Cost and production information should include:
Yield per acre
Value of crop per unit
Pumping costs (energy costs)
Initial investment cost
Labor costs - hours/irrigation
irrigations/year
costs/year/acre
Depreciation costs
System maintenance costs
The cost information is necessary to compare an existing
irrigation system with a proposed system. If upgrading
an existing system or converting to a new system is
recommended for solving a return flow problem, implementation
and operation and maintenance costs must be considered
for determining cost-effectiveness and farmer acceptance.
34
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2.2.4 Drainage Methods
In many areas, artificial drainage systems have been
installed to prevent the water table from becoming
too close to the surface. These systems are designed
and installed on an individual farm basis, or through
drainage districts. In many areas the Soil Conservation
Service (SCS) designs these systems for farmers and,
as a result, is a good source of information to locate
subsurface drains. Drainage districts can provide
similar information.
2.2.5 Irrigated Areas
The irrigated area in a region may be defined either
through mapped data or through statistical data.
Statistical Data
Statistical data is readily available from either the
Census of Agriculture, published by the U.S. Department
of Commerce, or from various state departments of
agriculture. This data is on a county-wide basis. For
studies of agricultural return flows, it is desirable
to have data on a basis of various sub-basins involved
rather than by county. This data is not readily
available as statistical data, but it can be obtained
from mapped data.
Mapped Data
Mapped data is available from several sources at various
levels of detail. The Soil Conservation Service has
made county-wide land use maps for many areas. These
maps have a scale of 1:126,720 (1/2-inch per mile).
While these maps provide a good overall picture of the
area, the level of detail may not be as high as desired.
In areas undergoing irrigation development, the information
may not be as up-to-date as is desired. Still, these
maps provide the best readily available information on
irrigated areas. These maps are generally available from
local or state Soil Conservation Service offices, or from
U.S. Department of Agriculture-Soil Conservation Service,
Cartographic Unit, Western Regional Office, Portland, Oregon.
35
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A higher level of detail is available from the aerial
photographs (approximately 8 inches = 1 mile) which
are maintained on file by the U.S. Department of
Agriculture, Agricultural Stabilization and Conservation
Service, and by the Soil Conservation Service. These
aerial photographs provide the best information in
locating the irrigated area. These photographs are not
usually collated onto a larger map. Other aerial
photography and remote sensing data is available from
the U.S. Geological Survey and N.O.A.A. (Department of
Commerce).
State and county land-use agencies represent another
potential source of data for defining the irrigated area.
2.2.6 Climatic Conditions
This information is readily available from the National
Weather Service, U.S. Department of Commerce. Length of
growing season, annual precipitation, and wind information
are necessary for analysis.
2.2.7 Soils Data
Soils data is available from the U.S. Department of
Agriculture Soil Conservation Service. In most irrigated
regions, this data is quite comprehensive and may be
obtained in various levels of detail. In most cases,
the general soil associations will provide sufficient
detail for problem definition. Relevant soil characteristics
include permeability, depth to impermeable layers, and any
chemical characteristics which might be responsible for
the impairment of water quality, such as high sodium or
salinity content.
2.2.8 Geologic Data
Geologic data is available from either the U.S. Geological
Survey or the Geological Survey of the various states.
The analysis of geologic data would be limited to
identifying bedrock and identifying the impact that these
bedrock formations might have on water quality. Where
well development is significant, it is important to
identify aquifers, the quality of water in individual
aquifers, and uses of the water in the aquifers.
36
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2.2.9 Chemical Use
Fertilizer
Fertilizer-use data may be difficult to find on a
detailed basis. On the regional basis, soils labs,
fertilizer dealers and extension agents may recommend
application rates and timing to farmers for various
crops. Such data does not verify actual practices,
however. Some interviews with farm operators are
necessary to obtain information on actual fertilizer
use.
Pesticides
As with fertilizer data, pesticide use data can
be difficult to obtain. Consultation with dealers,
crop dusters, extension agents and others can probably
provide the best information.
2.3 PROBLEM DEFINITION
Problem areas are areas with common conditions of
agricultural practices, soils, and other factors which
share common pollutant problems. A data collection and
analysis program such as discussed here and in Chapter
4.0 will provide the tools for problem definition.
Figures 4-7 and 4-8 display analysis leading to problem
area definition.
The key to problem area definition is to have a base map
of the irrigated area with transparent overlays displaying
soils, geology, and water quality data. Water supply
information and other data may also be of value. The
information thus organized can be used to compare
existing water quality with water quality goals.
Information gained on the irrigation system can then be
used to assess the water quality (and quantity) limitations
necessitated by irrigation, as well as avoidable water
quality limitations.
37
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The accumulated information may then be used to
develop priorities. Priorities may develop naturally,
or may be established through matrix analysis.
Evaluation criteria stem from national, regional,
and on-farm goals.
38
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3.0 DEFINITION OF BEST MANAGEMENT PRACTICES
FOR IRRIGATED AGRICULTURE
The term "best management practices" (BMP) means a
practice, or combination of practices, that is determined
by a State (or designated areawide planning agency)
after problem assessment, examination of alternative
practices, and appropriate public participation to be
the most effective, practicable (including technological,
economic, and institutional considerations) means of
preventing or reducing the amount of pollution generated
by non-point sources to a level compatible with water
quality goals. (40 CFS Part 130)
In order to select the best management practices,
control options must be compared. Suggested comparison
criteria are:
Costs
On-farm benefits
Effectiveness in improving water quality
Legal constraints
Institutional constraints
Social acceptability
Costs, benefits, and effectiveness are important, and
this manual is directed towards evaluation on this basis.
Nevertheless, the remaining criteria cannot be overlooked.
Figure 3-1 shows the processes leading to definition of
best management practices.
In most cases, a control option is either legally acceptable
or it violates existing laws. If legal constraints impose
too great an obstacle for implementation, other options
should be evaluated. Water allocation laws and water
quality laws'that have built-in hindrances to BMP
implementation are examples of legal constraints.
39
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—
D
DEFINITION
OF
PROBLEM
AREAS,
PRIORITIES
ON-FARM
PRACTICES
IN
PROBLEM
AREAS
OFF-FARM
IRRIGATION
DRAINAGE
SYSTEM
IN
PROBLEM
AREAS
SOILS,
GEOLOGY
OF
STUDY
AREAS
POLLUTANT
LOADING
MECHANISMS
EFFECTIVENESS
OF
BMP'S
IN PROBLEM
AREAS
COST
OF
BMP'S
'0
D
D
Q
a
LEGAL
SOCIAL
ANALYSIS
OF
BMP'S
DEFINITION
OF
BMP's
FIG. 3-1. BMP MANUAL METHODOLOGY -
DEFINITION OF BEST MANAGEMENT PRACTICES
toups
corporation
lov«land, co.
40
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Once it is determined that there are no significant
legal barriers, the options can be compared based on
costs, benefits, effectiveness, and institutional
constraints. Costs can usually be assigned dollar
values and include capital costs, operational costs,
and labor costs. Benefits include improved water
quality, increased crop yields, conservation of water,
and others.
Institutional constraints are factors which impede
timely implementation. Permits may be required, water
rights transferred, or variances obtained.
3.1 SUB-REGIONAL VS. ON-FARM EVALUATION
This manual recognizes two levels of best management
practices evaluation: sub-regional and on-farm. The
purpose of sub-regional evaluation is to provide guide-
lines and technical data which can be used for on-farm
evaluation and which are in accordance with recognized
goals. The purpose of on-farm evaluation is to select
best management practices which have been determined to
be effective in sub-regional analysis and are suitable
to the particular farming situation.
The sub-regional evaluation should then result in:
Definition of problem areas
Definition of best management practices
and guidelines for their use.
Intermediate data generated in the process of developing
a sub-regional plan forms the basis for on-farm evaluation.
This information includes:
Information on practices and natural
conditions contributing to excess
pollutant load in problem areas.
Information on effectiveness of control
options in light of practices and natural
conditions.
Cost data to be used in evaluation of BMP's.
41
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The sub-regional analysis may thus provide the
guidelines for the field technician to use in suggesting
best management practices to the farmer. It is
anticipated that this can be conducted in much the
same manner as soil conservation plans are currently
developed by the Soil Conservation Service.
3.2 DEFINITION OF POLLUTANT PATHWAYS
An irrigation return flow system may be very complex
for a problem area. Numerous irrigation practices
and environmental conditions can result in increased
pollutant levels for each parameter through all five
return flow paths (Figure 3-2).
Table 3-1 summarizes factors which contribute to
pollutant loading. The potential for certain pollutant
loadings exists because of the type of irrigation
practice, i.e., the potential for sediment pollution
always exists when there is surface irrigation on steep
slopes, but not when subsurface irrigation is practiced.
Each pollutant can be associated with certain return
flows. If salinity problems exist, the primary return
flow mechanism would be deep percolation. Tailwater and
bypass water would not be applicable. Table 3-2 associates
the common pollutants with possible loading mechanisms.
Pollutant information is detailed in Chapter 5.0.
3.2.1 Quantification of Pollutant Loading Mechanisms
Figure 3-3 shows an example of how several existing
practices can be related to one pollutant or how one
practice can cause more than one pollution problem.
Before control options can be evaluated, these pollutant
pathways must be quantified. This process may require:
Irrigation efficiency studies
Conveyance efficiency studies
Return flow quality determination.
Since loading processes for each pollutant are different,
it is necessary to consider the pollutants separately.
42
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CANAL
SEEPAGE
LEACHATE FROM
IRRIGATED FIELDS
SURFACE
RUNOFF FROM
IRRIGATED
FIELDS
5
FIG. 3-2. MAJOR POLLUTANT PATHWAYS
toups
corporation
lov«land, co.
43
-------
TABLE 3-1. SUMMARY OF FACTORS CONTRIBUTING TO POLLUTANT LOADING
SOILS
TOPOGRAPHY
GEOLOGY
IRRIGATION
METHOD
WATER
SUPPLY
IAND USE FERTILIZER IRRIGATION
USE EFFICIENCY
SOILS TOPOGRAPHif GEOLOGY
Heavy Light Non-saline Saline
(fine) (sandy) Steep Flat Formation Formation
•g
•6 3 £.•
4J D 5S fl .
•^SS «}-.
H.8-S U Ji-
ll
l§
Salinity
Nitrates
Sediment
Phosphorous
X
X
X
X
X
X
X
X
X
X
-------
TABLE 3-2. LOADING MECHANISMS FOR POLLUTANTS
ASSOCIATED WITH IRRIGATION RETURN FLOW
Pollutant
Salinity
Nitrates
Sediment
Phosphorous
Pesticides
Associated
With Surface
Runoff
(Tailwater)
X
X
X(l)
Associated
With Leachate
From Irrigated
Fields (Deep
Percolation or
Artificial
Damage)
X
X
X(l)
Associated Associated
With Canal With Bypass
Seepage Water
X(2)
X(3)
X
(1) Loading mechanism varies with characteristics of
particular pesticide.
(2) Only when contributing to groundwater which becomes
consumptively used in wet areas or where saline subsoils exist.
(3) Primarily where nitrogen is applied with irrigation water.
45
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-EXISTING
PRACTICES-
NITROGEN
ADDITION TO
HEAD DITCH
WATER
NITROGEN
FERTILIZER
TO SOIL
SURFACE
HIGH
NITROGEN
USE
-RETURN FLOW-
-POLLUTANT-
BYPASS
WATER
TAILWATER
\
Illl
Humming
X
NITRATES
LOW IRRIGATION
EFFICIENCY
(LEACHATE)
LIGHT
SOILS
*\
••"••iiiiiiiiiiift
DEEP
PERCOLATION
•EXISTING
PRACTICE-
OR
•RETURN FLOW-
-POLLUTANTS-
PESTICIDES
FURROW
IRRIGATION
WITH STEEP
SLOPES
lllllllllllllllilil
TAILWATER
liilllliiliiiiiini
PHOSPHOROUS
\
SEDIMENT
FIG. 3-3. EXAMPLES OF INTERRELATIONSHIPS
toups
corporation
lov«land, eo.
46
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Salinity
In all irrigated areas, the primary cause of increased
salinity is concentration through consumptive use. In
most areas, this is the only significant cause of
higher salinity levels. In such cases, the total salt
load, expressed in tons, is not increased through the
system.
Where salt concentrations are increased only through
cropland consumptive use, little potential for improvement
exists. What potential does exist will have to be
determined through greater study of the effect of
leaching fraction on salt load under local soil and water
conditions.
In a few irrigated areas, however, salinity problems may
be added to by non-beneficial consumptive use or by
dissolving salts (pickup) from saline subsoils. In such
cases, attempts should be made to quantify the pollutant
load resulting from conveyance systems, excess leaching
of irrigated land and evaporation and phreatophyte use.
Determination of the quantity of water taking each
pathway first requires a system inventory of the problem
area. Quantities which should be determined or estimated
are:
Length of major canals in problem area
Length of laterals in problem area
Length of on-farm head ditches in the
problem area
Irrigated acreage in the problem area.
In order to arrive at a common denomination for control
option evaluation, it is desirable to express canal
length as the amount needed to service a unit of irrigated
land. Thus, if 10 miles of laterals serve 6,000 acres,
there are .0016 miles of canal per irrigated acre.
Costs of improvements per mile can be converted to per
acre cost in this manner.
47
-------
Determination of the resulting pollutant load requires
knowledge of the quality of these waters, as well
as of the quantity. These quality changes must be
observed through intensive research and sampling programs.
Nitrates
Nitrate loading results primarily through leaching of
irrigated soils. Soils where nitrate problems exist
tend to be light and well drained, factors which make
it easy to apply excessive water. Control options which
reduce excessive leaching may generally be evaluated in
terms of a proportional decrease in nitrate loading.
Those control options which do not reduce leaching but
alter fertilizer practice are much more difficult to
evaluate, requiring experimental evaluation.
The effectiveness of nitrate control options is highly
dependent upon soil conditions. As a result the loading
of nitrates as a function of fertilization has produced
mixed results (see Chapter 4.0).
Sediment, Phosphorus, and Sediment Associated Pesticides
Tailwater is the primary loading mechanism for these
pollutants. Those control options which reduce tailwater
volume can be expected to reduce loading of these
pollutants by at least an equal percentage. Reductions
by a greater percentage is possible since runoff stream
velocities are generally reduced. Sediment ponds, filter
strips and grassed waterways have a wide range of effects
depending upon local conditions. These are discussed in
Chapter 4.0.
3.3 CONTROL OPTION EFFECTIVENESS EVALUATION
Since it may not be possible to implement every control
option, the following questions should be addressed:
1. What percentages of the total pollutant
loading can be attributed to pollution caused
by irrigated agriculture?
48
-------
2. How can the pollutants be ranked in
terms of their impact on beneficial use
or seriousness of water quality degradation?
3. What percentage reduction of each pollutant
can be attained by each control option?
4. Which options can result in the most benefits
(greatest reduction in pollution) for the
least dollars spent?
The effectiveness of control options in meeting water
quality goals can be compared in a similar manner for
one field or for the sub-basin. Effectiveness should
be evaluated in terms of the importance of a particular
pollutant and the potential for reduction of that
pollutant. Such analysis should be conducted for each
prospective control option. Each control option is
discussed in Chapter 5.0 in terms of applicability
and effectiveness.
3.3.1 Control Option Effectiveness Determination
Control options can be compared in terms of their
potential reduction in pollutant loading. Table 3-3
displays an example of an analysis of the effectiveness
of control options. This type of evaluation requires a
considerable knowledge of the changes which are likely
to occur upon implementation of BMP's. Development of
this information must be conducted at the sub-regional
level due to the level of technical information required.
The effectiveness of control options is a result not only
of the change in hydraulic loading, but also of the change
in quality. The change in hydraulic loading is fairly
easy to identify. The change in the quality of return
flows is not so easy to identify and will likely require
a research effort, especially for salinity.
49
-------
In Table 3-3 we see the various parameters which need
to be identified. In this example, the estimated
subsurface return flow volume is 1000 acre-feet over a
specified area. Of this 1000 acre-feet, canals, laterals
and on-farm ditches each contribute 100 acre-feet.
Leaching of irrigated fields contributes 70 percent
of the total load to groundwater, or 700 acre-feet.
These estimates can be made from irrigation efficiency
studies, and from conveyance efficiency studies.
The reduction in hydraulic load resulting from each
control option (column 3) can be estimated with a fair
degree of accuracy, based upon comparison of existing
efficiencies with projected improved efficiencies
resulting from application of best management practices.
In this example, it is assumed that furrow irrigation
is used, and that the average leaching volume is 0.4
acre-ft/acre. It is estimated that sprinkler irrigation
without irrigation scheduling could safely reduce this
to 0.3 acre-ft/acre, a 25 percent reduction (column 3).
The area is served by a canal which supplies 500 mg/1
TDS water. This is relatively constant through the
system. Samples from the groundwater directly below
the canals indicate that the seepage water has increased
to 700 mg/1 as a result of phreatophyte use or salt
pickup (column 5).
The quality of return flows resulting from leaching of
croplands has been found to be about 2000 mg/1 TDS. It
is not expected that irrigation scheduling will change
the leaching fraction sufficiently to change this
quality. Sprinkler irrigation is expected to reduce
the leaching fraction sufficiently to increase the
concentration to 200 mg/1. Total loading (quantity x
quality) would be less, however.
It is in determining the quality of return flows that
significant uncertainties come into the picture. It is
quite difficult to assess the quality of returns under
existing conditions, and very difficult to predict the
quality of returns under other leaching conditions.
Uncertainties are had in knowing what exactly is being
sampled, hydrologic variations, and variations in human
input. Research at the sub-regional level will probably
be required in order to obtain figures which have validity.
50
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TAKE 3-3 CONTROL OPTION EFFECTIVENESS COMPARISON - EXAMPLE: SALINITY
Practice
CONVEYANCE SYSTEM
BJPROVEMENT
Canal Line
Lateral Line
Ditch Line
IN-FIELD
PRACTICES
Irrigation
Scheduling
Sprinklers
Sprinklers With
Scheduling
Level Basin
Level Basin
With
Scheduling
1
Total
Subsurface
Return Flow
Volume -
Ac-Ft
(Existing
Condition)
1,000
1,000
1,000
1,000
1,000
1,000
1,000
1,000
2
Fraction
of Total
Hydraulic
Loading
Contributed
By This
System
.10
.10
.10
.70
.70
.70
.70
.70
3
Reduction
In Hydraulic
Load With
Control
Option
(Fraction)
.9
.9
.9
.1
.25
.30
.25
.30
4
Quality
of Input
Water
mg/1 TDS
500
500
500
500
500
500
500
500
5
Quality
of Return
Flow
Existing
Practice
mg/1 TDS
700
700
700
2,000
2,000
2,000
2,000
2,000
6
Quality
of Return
Flow
With
Control
Option
mg/1 TDS
700
700
700
2,000
2,100
2,100
2,100
2,100
7
Salt Load
Existing
Practice
(Tons)
95
95
95
1,904
1,904
1,904
1,904
1,904
8
Salt Load
With
Control
Option
(Tons)
71
71
71
1,761
1,618
1,542
1,618
1,542
9
%
ReductLc
In
Load
1
1
1
6
13
16
13
16
Column 7 = Column 1 (ac-ft) x Column 2 x Column 5 (mg/1) x 1.36 x 10~3 = Tons
Column 8 = Column 1 (ac-ft) x Colunn 2 x (1 - Colunn 3) x Column 6 x 1.36 x 10~3 + Column 1 x Column 2 x Column 3 X Column 4 x
1.36 x 10~3 = Column 1 (ac-ft) x Column 2 x 1.36 x 10~3 [(1-Coluron 3) x Column 6 + Coluttn 3 x Column 4)3 = Tons
Column 9 = °^?!"^Z-iI 9^J!f9-?i «™,rv~>«,\ Here tot*1 salt load = 95 canals + 95 laterals + 95 ditches + 1,904 field leaching - 2,189
-------
For salinity, it is recommended that guarded pessimism
be used in predicting reduction in pollutant load.
Improved irrigation practices can be effective in
reducing total salt load, yet any significant reduction
in leaching fraction (hydraulic loading) can be expected
to result in an increase in salinity of the leachate.
This increased concentration may be accompanied by an
undesireable change in the ionic composition of the
water, due to precipitation of less soluble ions in the
soil.
Practices for control of nitrates can be evaluated in
much the same manner as displayed in Table 3-3. Nitrate
analysis is much easier, since the concentration of
nitrates in the leachate is less influenced by leaching
fraction. Prediction of results obtained by altered
fertilizer practices may be more difficult.
Sediment and phosphorous control practices may be
evaluated by similar procedures.
3.3.2 Effectiveness in Meeting Regional Goals
Regional goals may be the result of in-stream water
quality or downstream water uses. Definition of these
conditions will aid in the definition of water quality
goals. The potential for improvement may then be
considered based upon pollutant source and potential
for reduction in pollutant loading.
The program for irrigated agriculture should be defined
so that the selected best management practices are
effective towards meeting water quality goals. Some
goals may be achieved, and other water quality problems
may not be significantly reduced even with a high level
of effort. Salinity is generally an example of where
a high degree of effort may result in only marginal
improvement.
The existance of several goals for pollutant loading
reduction from irrigation returns may make best management
practices which are effective for more than one pollutant
highly desireable. Also, the existance of several goals
may require that a level of effort for each of the several
goals be defined.
52
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3.3.3 Determination of Sub-Regional Best
Management Practices
Sub-regional best management practices must also be
evaluated in terms of cost-effective, institutional,
social, and legal constraints. The cost-effectiveness
of sub-regional best management practices can be
evaluated using an objective analysis. While most
best management practices will have to be tailored to
specific farming situations, a sub-regional analysis
identifies those practices effective in meeting water
quality goals in a region.
A sub-regional analysis is displayed in Table 3-4. In
this table, acreage recommendations and estimated
participation are included so that regional costs can
be estimated. The computed cost is a function of these
participation levels. As a result, the effectiveness-
cost ratio is independent of participation levels and
recommended acreages.
The effectiveness ,cost.ratio and ranking can be computed
either as a function of the ratio of effectiveness to
total cost or as the ratio of effectiveness to costs in
excess of non-water quality benefits (net cost
attributable to water quality). Decision of priorities
then requires some subjective decisions. Alternatives
which appear good in some ways may be discounted due to
legal, institutional, or social constraints or possibly
due to energy requirements.
3.3.4 Estimation of Reduction in Pollutant Loading
By combining the expected result from each installation
of a practice (Section 3.3.1) with the expected
participation levels developed for Table 3-4, it is
possible to estimate the reduction in the loadings of
a particular pollutant. This represents an areawide
quantity, and does not represent the change in load
on the receiving waters. Nutrients and sediment are
non-conservative, and re-use of the results in a reduction
in loading. Prediction of improvement of in-stream
quality must account for these factors as well as total
loading.
53
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TABLE 3-4.
RANKING OF SUB-BASIN ALTERNATIVES AND COST ESTIMATION
cn
d) (2) (3)
Control Effectiveness Percent of
Option in Meeting Irrigated
A
B
C
D
Regional Acreage
Goals for which
practice
is
recommended
(or % of
Ditch length)
(percent)
1.159 50
0.20 60
0.10 70
0.05 30
(4) (5) (6)
Estimated Combined Equivalent
Participation Effective- Annual cost
at prescribed ness
level of cost
sharing
(percent)
20 .0159
50 .06
90 .063
40 .006
at expected
level of
Implementation
(thousands)
20
40
30
10
(7) (8)
Direct Effectiveness
Annual Cost Ratio
Benefits
(thousands) E E
C C-B
X10-6 X10-6
10 .795 1.59
5 1.5 1.7
10 2.1 3.15
8 0.6 3.0
(9)
Rank
E E
C C-B
3 4
2 3
1 1
4 2
TOTAL COST OF PROGRAM
NOTES:
(Column 1) - All options can be compared regardless of
the subsystem problem they address.
(Column 5) - Product of Columns 2, 3, and 4.
(Column 6) - Unit cost x total acreage x Column 3 x
Column 4. Total length of ditch may be
substituted for total acreage.
(Column 7) - Direct annual benefits other than water
quality including:
o Reduced operational expense
o Increased crop yields
Water savings may or may not be accounted
for as benefit.
(Column 8) - The effectiveness-cost ratio may be determined
using either the total cost or the cost not
directly attributable to other benefits, i.e.,
Column 5 Column 5
Column 6 Column 6 or Column 7
(Column 9) - Alternative ranking may be done by either of
the above methods.
-------
3.3.5 Determination of On-Farm Best Management Practices
It is recommended that best management practices for
a particular farm be evaluated in terms of their
effectiveness in meeting water quality goals in
relation to their net cost. This evaluation procedure
is geared to a voluntary program where cost-sharing
is used as an incentive. Legal, institutional,
and social constraints must be taken into account
when evaluating on-farm improvements.
The farmer or landowner, when evaluating an improved
practice, wants to make the benefits exceed his costs.
That is:
B > CA
Where B = Annual dollar benefit of
increased yield, and decreased
operational expense.
CA = Equivalent annual cost to the
farmer.
Specific costs associated with control options are
discussed in Chapter 5.0. Implementation of BMP's on
a voluntary basis can only be expected when net benefit
to the farmer can be demonstrated.
Benefits to the nation occur as improved water quality
and better utilization of water resources. Assignment
of dollar values to these parameters is possible, but
often difficult and inaccurate. Money spent for pollution
control should achieve a high degree of effectiveness per
tax dollar, or:
Cp
Should be large compared to other alternatives. Where
55
-------
E = Comparitive effectiveness in meeting
regional water quality goals.
Cp = Equivalent annual cost to the public.
3.4 CASE STUDY - BEST MANAGEMENT PRACTICES FOR
IRRIGATED AGRICULTURE IN THE LARIMER-WELD
REGION OF COLORADO
Much of the methodology presented in this manual is
the result of work conducted by the consultant in
developing a BMP plan for the Larimer-Weld Regional
Council of Governments (LWRCOG). Toups Corporation
conducted this work under two separate contracts.
The first contract, initiated in the summer of 1976,
was a result of the water quality planning program
being conducted by the LWRCOG under Section 208 of
P.L. 92-500. This contract resulted in the report,
"Water Quality Impacts of Irrigation Return Flow in
the Larimer-Weld Region." A second contract awarded
Section 104-b funds to the LWRCOG in order to define
"Best Management Practices," including social, insti-
tutional, and financial roles for the region. This
section contains a brief review of the experiences of
the consultant in carrying out these contracts.
3.4.1 Water Quality Impacts of Irrigated Agriculture
Analysis of the Water Quality Impacts of Irrigated
Agriculture in the region consisted of:
Analysis of irrigation practices;
Hydrologic analysis;
Water quality analysis of discharges
and receiving waters;
Analysis of water quality problems
associated with irrigation return flows.
The analysis of irrigation practices consisted of
collecting data from several sources. Soils data,
geologic data, and data on the irrigated area and
canal system were all mapped. Information on ferti-
lizer and pesticide use was collected through inter-
views with farmers, crop-dusters, and others.
56
-------
The area consists of approximately 500,000 irrigated
acres, with surface water being the principal water
source. Surface irrigation is used on over 90 percent
of the irrigated land.
Hydrologic analysis consisted of gathering data on
the location and amount of returns and diversions.
Major surface drains entering the river were measured
and quality samples taken. Groundwater inflows to
the rivers were quantified through inflow-outflow
analyses. The maintenance of records of surface water
diversions by the State Engineer allowed flow routing
through the river system. Irrigation diversions dry
up rivers throughout the region, in the summer for
irrigation and in the winter for storage.
Water quality analysis consisted of taking samples of
rivers, drains, and other discharges. Approximately
150 sampling sites were utilized with flow measurements
incorporated at each. In this way, the water quality
sampling program was tied to the hydrologic analysis.
The water quality sampling pointed to specific problems
in the region whiTch could be typified by soils,
geology, irrigation method and other agricultural
practices.
Data obtained on soils, geology, hydrology, water
quality, and practices was mapped and displayed graphically
in a method similar to that displayed in Section 4.2
of this document. Conclusions from this analysis Were:
Hydrologic impacts of irrigation are
the major impediment to water quality.
Streams in the irrigated portion of the
region are repeatedly dried up by
diversions. Below these points, irrigation
return flow is the only source of water to
the region.
57
-------
Areas which were shallow to certain
cretacious formations were found to
have highly saline groundwater (E.G.
greater than 5000 umho/cm) despite good
quality supply water (EC less than
500 umho/cm). Problems resulting from
contact of irrigation seepage water
with the saline groundwater were high
salinity in subsurface drainage returns
and numerous salt seep areas (high
water tables).
Concentrated cattle feeding operations
in the Greeley area resulted in enormous
manure output. Transport expenses
resulted in most of this manure being
used within 7 miles of the source.
Typical fertilizer practice in this area
was 15 to 20 tons of manure/acre each
year plus 150 pounds of N applied as
chemical fertilizer plus about 50 pounds
of N applied as anhydrous ammonia in the
irrigation water. Soils were generally
sandy loam. High nitrates were observed
in subsurface drain discharges in this area.
Sediment problems were especially pronounced
along one of the smaller rivers, the Little
Thompson. Here, cultivation and surface
irrigation were practiced right up to the
river banks. Sediment problems in other
areas were much less due to interception
of returns by lower ditches, and the
existance of a non-irrigated flood plain.
3.4.2 Best Management Practices - Pollutant Loading
Mechanisms
The Best Management Practices program consisted of an
in-depth analysis of practices contributing to the
identified problems as well as an analysis of options
which could reduce the pollutant load.
58
-------
Irrigation efficiency and water quality determination's
were made with each irrigation on four study farms.
Two of the farms were studied for salinity - one
for nitrates and one for sediment. Flows both onto
and off of the field were measured and sampled.
Observation wells and soil moisture extractors
allowed the sampling of groundwater and soil moisture.
Canal seepage determinations were also made. The
information gained in the program allowed quantification
of pollutant loading mechanisms. Mechanisms for
salinity and nitrates were:
In areas with salinity problems, salt
concentrations in leachate from the root
zone were much lower than concentrations in
the groundwater. Groundwater concentrations
were the result of precipitated salt,
weathering of parent shales, and non-
beneficial consumptive use where high
water tables existed. Excess water use
was not a problem due to limited supply,
but distribution efficiencies (coefficient
of uniformity) were hampered by excessive
or irregular slope.
Since all waters entering the groundwater
became part of the saline groundwater, it
was determined that the problem could best
be reduced by reducing the non-beneficial
loss of surface water to groundwater.
Underestimation of the nitrogen value was
combined with poor irrigation efficiencies
on sandy soil caused by excessive length of
run. Leachate contained an average of
50 mg/1 of NO3 + NC>2 as N on one field.
Best Management Practices were evaluated for their
cost and their ability to reduce the pollutant load.
The mechanics of this analysis follow.
59
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3.4.3 Cost Effectiveness for BMP's in Larimer-
Weld Region
There are eight basic Best Management Practices which
have been evaluated as to their pollutant reduction
and cost effectiveness. These BMP's have been
implemented to varying degrees in the Larimer-Weld
Region for water conservation and labor saving reasons.
They are also effective in reducing pollutant loadings.
Conveyance system improvements consist of converting
earthen-lined head ditches, laterals, and canals to
either concrete lined structures or pipelines. This
has the effect of reducing seepage losses by 90 percent
and erosion problems of 100 percent. By reducing
seepage, the flow of groundwater across subsurface
shales is reduced, thereby reducing salt pickup by the
groundwater which ultimately finds its way to surface
waters. Also, preventing seepage conserves water making
it available as a dilutent in surf-ace waters. This control
option is valid only in areas with subsoil salinity
problems or many seep spots.
Sprinkler irrigation systems have long been used in
conjunction with groundwater supplies. They have
proven to be more efficient than surface systems.
Technology now exists to convert surface systems to
sprinkler systems; being more efficient, less excess
leaching and surface runoff occurs. By decreasing
field leaching, salinity and nitrate loading are
decreased and by reducing field runoff, sediment,
phosphorous, and pesticide loading are reduced.
Water management improvements include irrigation
scheduling, water measurement devices, and irrigator
education programs. Each must be practiced before more
efficient irrigation can be realized. Increased
application efficiencies can minimize excess leaching
(deep percolation losses) and field runoff (tailwater).
60
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System efficiency improvements include such practices
as cut-back furrow irrigation, shortening length of
runs, and modifying field layout and furrow directions.
These improvements can also increase irrigation
application efficiencies.
Tailwater control practices reduce field runoff -
sediment loss (loading), phosphorus, and pesticide
pollution. Since phosphorus and most pesticides are
transported with sediment, sediment control will solve
these problems as well. Four methods were included in
the analysis: 1) sediment ponds; 2) tailwater recycling;
3) buffer/filter strips; 4) grassed waterways.
Fertilizer management consists of using slow release
nitrogen fertilizers and/or applying fertilizer at
times when it can be used by the crop. The goal is to
reduce nitrate loss through leaching to groundwater.
Less amounts of fertilizer could be used or higher crop
densities could be attainable.
Land leveling is a practice which can eliminate "seep
holes", decrease slopes, or otherwise make possible more
uniform irrigation in furrow or flood systems. This can
reduce excess leaching and tailwater loss.
Drainage systems can lower groundwater tables and serve
as collection drains for salt and nitrate laden seepage
water. Lowering water tables helps keep land in
production and collection of seepage water reduces water
available for salt pick-up for transporting nitrates to
groundwater supplies.
Table 3-5 summarizes the relationship between control
options and pollutants for the Larimer-Weld region. This
table contains regional input, since recognized problems
are incorporated. As an example, conveyance systems
were considered to be effective for salinity control within
certain portions of this region, but they are not
universally effective.
61
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TABLE 3-5. POLLUTANTS AFFECTED BY BMP' S
CTi
to
7
8
BEST MANAGEMENT PRACTICE Salinity Nitrates
Conveyance System Improve-
ment
Ditch lining or pipeline CS(2)
Lateral lining or pipe- CS
line
Canal Lining
CS
*
FL(4)
FL
FL
Convert to sprinklers
Sprinklers with water
management
Water Maragement
Irrigation scheduling
Water measurement devices
Education programs
System Efficiency Improve- FL
rnen'cs
Tailwater Control
Sediment ponds
T.W. recycling
Duffer/filter, stri p
Grassed waterways
I-VTti lizer Management
release nitrogen)
FT:
FL
Land Leveling
Drainage Syste/ris
FL
FL
FT,
FL
FL
POLLUTANT
Sediment (1) Phosphorus (1) Pesticides (1)
CE(3)
CE
CE
FR(5)
FR
FR
FR
FR
FR
PR
FR
FR
FR
(1) Best I-lanagement practices which control sediment
loading, also control phosphorus and pesticide loading.
(2) CS - Conveyance Seepage
(3) CE - Conveyance Erosion
(4) FL - Field Leaching
(5) FR - Field Runoff
FR
FR
FR
FR
FR
FR
FR
FR
FR
FR
FR
FR
FR
FR
FR
FR
-------
BMP's have different effectiveness factors for
reducing loading of salinity, nitrates, and sediment.
In the analysis for the Larimer-Weld region, effectiveness
for salinity control was measured as the effectiveness
in reducing unnecessary water loss to the highly saline
groundwater which existed in certain areas. In other
areas, it was felt that salinity control measures would
not be effective.
Sprinkler systems with water management can reduce
water loss to the groundwater by about 25 percent
(0.245 effectiveness factor). Sprinkler systems without
water management and surface systems with water management
can reduce loading by about 20 percent (0.210 effectiveness
factor).
For nitrate loading, sprinklers with water management
are most effective (35 percent and 0.350), with sprinkler
systems without water management, surface systems with
water management, and fertilizer management all reducing
loading by 30 percent (0.300 effectiveness).
Since sediment pollution is more easily controlled,
several BMP's have high effectivness factors:
Sprinkler Systems 85% reduction 0.855
Sediment Ponds 63% reduction 0.630
Tailwater Recycling 63% reduction 0.630
Table 3-6 shows the development of effectiveness factors.
They have been developed as the product of the proportion
of pollutant load contributed by a system (conveyance,
field leaching, etc.) times the percent reduction in
pollutant load from that system.
The proportion of pollutant loading was developed
through study of both irrigation and conveyance efficiencies,
This data was combined with data on irrigated acreage
and total length of canals and laterals. In this way the
relative contribution of field leaching and conveyance
seepage could be determined.
63
-------
TABLE 3-6. LOADING-REDUCTION EFFECTIVENESS FACTORS
REDUCTION IN CONVEY-
ANCE SEEPAGE OR FIELD NITRATES
SEDIMENT
LEACHING FOR
BEST
MANAGEMENT
PRACTICES
Ditch Lining &
Pipeline
Lateral Lining
& Pipeline
Canal Lining
Sprinkler
Systems
Sprinklers with
Water Mgmt.
water Mgmt. Iivp.
Irrigation
Efficiency Inp.
Sediment Ponds
Tailwater
Recycling
Buffer/Filter
Strio
Grassed Waterways
Fertilizer Mgmt.
Land Leveling
Drainage Systems
SALINITY
0) — .
O< rH
3r-.fr.
s^'s
ft i-S
15(4)
5(4)
10(4)
70(6)
70(6)
70(6)
70(6)
0
0
0
0
0
70(6)
70(6)
CONTROL
ilrs
B °
So??
*r
90(5)
90(5)
90(5)
30(7)
35(7)
30(12)
10(12)
0
0
0
0
0
10(11)
10(11)
Field
ft
rrt tj*
-P fH C
Effective § .0 "<§
Factor S $ §
0.135 0
0.045 0
0.090 0
0.210 100(8)
0.245 100(8)
0.210 100(8)
0.070 100(8)
0
0
0
0
100(8)
0.070 100(8)
0.070 100(8)
Leaching
d>
5 9
g •£ Effective
P ,§ Factor
3 a)
0
0
0
30(9) 0.300
35(9) 0.350
30(12) 0.300
10(12) 0.100
0
0
0
0
30(9) 0.300
5(11) 0.050
5(11) 0.050
Field Runoff
ft
3n H1
\^ * * ^^
§^3
ft
0
0
0
90(10)
90(10)
90(10)
90(30)
90(10)
90(10)
90(10)
90(10)
0
90(10)
0
&C
JS 2
G 5
(D ly
PI fy
100
100
100
95(11)
95(11)
50(13)
50(13)
70(11)
70(11)
35(11)
30(11)
0
5(11)
0
Effective
Factor
0.855
0.855
0.450
0.450
0.630
0.630
0.315
0..270
0.045
-------
TABLE 3-6. (CONT'D.) LOADING-REDUCTION EFFECTIVENESS FACTORS
(1) Percentage of total pollutant loading to groundwater
and/or surface water system attributable to an existing
practice.
(2) Percentage reduction in pollutant loading for each
pollutant as a result of BMP application.
(3) Effectiveness of BMP in reducing total oollutant
load ( (1) x (2) 7 100%)
(4) See Table 2-A, Table 2-B
Assume salinity loading to IRF (groundwater) is directly
proportional to seepage volumes within problem areas.
(5) Lining and/or pipelines reduce total conveyance seepage
by 90%.
(6) Contribution of field leaching is 70% of total loading.
See Table 2-B (leaching requirement + excess leaching).
(7) Without water management reduce excess leaching 80%
or 80% of 35% = 30%.
With water management reduce excess leaching 100%
or 100% of 35% = 35%.
(8) Assume 100% of nitrate loading to groundwater is from
a field leaching of nitrates.
(9) Assume nitrate loading 35% leaching requirement
35% excess leaching
30% nitrogen fertilizer
Without water management 80% of 35% = 30%
With water management 100% of 35% = 35%
(10) Assume 90% of sediment load is from irrigated
agriculture field runoff.
(11) From Toups
(12) 80% of excess leaching = 30%.
30% of excess leaching = 10%.
(13) Water management could reduce tailwater by at least 50%.
Cutback systems could reduce tailwater by at least 50%.
65
-------
In order to compare various BMP's and their
pollutant reduction effectiveness in terms of costs,
all costs have been reduced to cost per acre.
Some BMP's are capital intensive. Table 3-7 shows
costs/acre for these BMP capital investments. Land
leveling at $400/A. is highest, sprinkler systems
(center pivot) at $300/A second, and sediment ponds
$15/A least expensive.
Realizing canal sizes vary and center pivot sprinkler
sizes can range from 50 to 500 acres, etc., reasonable
average figures were used. Estimates of number of
miles of ditches, laterals, and canals were developed.
Equivalent annual costs for capital investments and
operation and maintenance (labor included) costs for
assumed 20 year life and projected useful life were
tabulated. Operation and maintenance costs were based
on percentages of total investments or labor costs.
Forty year useful life was used for each capital
intensive BMP except sprinklers and tailwater recycle
systems for which 20 years was used. Costs per acre
are on Table 3-8 and costs per unit are on Table 3-9.
Operation and maintenance and useful lives are shown
in their respective columns.
Several best management practices have benefits
associated with them, such as decreased labor, increased
crop yield, and decreased production costs. Estimated
benefits are presented in Table 3-10.
Operation and maintenance decreases are in the form of
less labor per acre per irrigation or less labor for
ditch maintenance. Increased crop yields per acre can
be attributed to more uniform application distribution
from sprinklers, timeliness of irrigations, elimination
of seep areas, more available water, and less nutrient
loss from excess leaching.
66
-------
TABLE 3-7. CAPITAL COSTS OF BMP ' S
BEST
MANAGEMENT
PRACTICES
COST/UNIT
UNITS/ACRE
COST/ACRE
Ditch Lining &
Pipeline (0-3 cfs)
Lateral Lining &
Pipeline (3-30cfs)
Canal Lining
Sprinkler Systems
Sprinklers with
water management
Water Mgmt.Imp.
Irrig. Efficiency
Imp.
Sediment Ponds
Tailwater Recycling
Buffer/filter strip
Grassed waterways
20,000/mile
40,000/mile
90,000/mile
40,000/sprinkler
40,000/sprinkler
1,000/pond
12,000 each
Fertilizer Management
Land Leveling 400/A.
Drainage Systems 20,000/mile
7 miles/640 A.
1.65 miles/640A.(!)
1.65 miles/640A.(1)
1 sprinkler/130A..
1 sprinkler/130A.
220
100
230
300
300
2/160A.
2/160A.
15
150
1 mile/80A.
400
250
(1) 1200 miles
714 miles2 = 1.65 imles/640A.
when
total length of laterlas or canals
irrigated acreage served by surface
water
67
-------
TABLE 3-8. ANNUAL COSTS PER ACRE
00
BEST
MANAGEMENT
PRACTICES
Ditch Lining & Pipeline
Lateral Lining &
Pipeline
Canal Lining
Sprinkler Systems
Sprinkler with Water
Mgmt .
Water Mgmt. Imp. (1)
Irrig. Efficiency (2)
Sediment Ponds
Tailwater Recycling
Buffer/filter strip (3)
Grassed Waterways (3)
Fertilizer Mgmt.
Land Leveling
Drainage Systems
Capital
Invest.
220
100
230
300
300
15
150
400
250
(DOLLARS /ACRE)
EQUIVALENT ANNUAL £
O & M 2QYr. Useful c
(Labor) Life Life
Yrs.
7 22
3 10
7 23
24 30
24 + 12 30
12
165
1 2
43 15
1
1
12 40
8 25
40
A SV
40
A S\
40
20
20
40
f\ r*
20
40
40
§ST : = ™- ~i
,,.__, 20Yr. Useful
LIFE Life Life
18 29
8 13
1 Q
19 30
30 54
on ->4
30 66
12
165
15
58
1
1
33
52
20
33
25
11
26
54
66
12
165
2
58
I
1
45
28
i = 7.75%
erf @ i, 20 yr = 0.0999
erf @ i, 40 yr - 0.0816
-------
TABLE 3-8. (CONT'D.) ANNUAL COSTS PER ACRE
(1) $12 annual cost includes purchase of flow measuring
devices, Irrigation Scheduling Service, and
Education Program.
(2) Double the 0 & M Cost (labor) of furrow irrigation
by cut-back operation on shorten length of run.
From Doanes OM = $82/A. for furrow irrigation.
(3) For filter strip 8.25 foot wide strip at bottom of
1/4 mile rows # of miles of strip = # of acres
taken out of production.
For each acre of crop 0.00625 acres = 0.001 A. are
taken out of production. Therefore, for corn at
$300/A. value cost is $.30/A.
Use maximum of $1/A.
Use same for grassed waterways.
69
-------
TABLE 3-9. ANNUAL COSTS/DOLLARS
-j
o
BEST
MANAGEMENT
PRACTICES
Ditch Lining & Pipeline
Lateral Lining &
Pipeline
Canal Lining
Sprinkler Systems
Sprinklers without
Water Mgmt.
Water Mgmt. Imp.
Irrig. Efficiency Imp.
Sediment Ponds
Tailwater Recycling
Buffer/filter strip
Grassed waterways
Fertilizer Management
Land Leveling
Drainage Systems
Capital O
Costs
20,OOD/mi.
40,000/mi.
90,000/mi.
40,000/mi.
1,000/unit
12,000/unit
400/A.
20,000
& M
Costs
600
1200
2700
3200
12
165
60
720
12=10
600
Annual
Costs
20 Yr.
Life
2000
4000
8990
4000
100
120
40
2000
Annual
Costs
Useful
Life
Years
40
A f\
40
A /S
40
20
40
f\ r\
20
40
40
Total
Annual
Costs
An. Cost 20 Yr.
for Use- Life
Total
Annual
Costs
Useful
Life
ful Life
1630
3260
7340
4000
80
120
30
1630
2,600
5,200
11,690
7,200
160
840
50
2,600
2,230
4,460
10,040
7,200
140
840
40
2,230
i = 7.75%
erf @ i, 20 yr. = 0.0999
erf @ i, 40 yr. = 0.0816
-------
TABLE 3-10. BENEFITS PER ACRE
BEST
MANAGEMENT
PRACTICES
Ditch Lining or
Pipeline
Lateral Lining or
Pipeline
Canal Lining
Sprinkler Systems
Sprinkler with water
mgmt.
Water mgmt. improvement
Irrigation efficiency
improvement
DOLLARS/ACRE /YEAR
Decrease
O&M
(Labor)
10(1)
5(3)
5(4)
75(5)
60(7)
Increase
Crop
Yield
30(6)
30(8)
30(9)
30(10)
Total
Other Annual
Benefit Benefit
15(2) 25
5
5
105
90
30
30
Sediment Ponds
Tailwater Recycling
Buffer/filter strip
Grassed waterways
Fertilizer management
Land Leveling
Drainage Systems
30(4)
5(12)
15(13)
15(14)
30
5
15
15
Average crop yield (value) per acre = 30.6 + 151.9 - 17. 6_
500,000
71
-------
TABLE 3-10. (CONT'D-) BENEFITS PER ACRE
(1) $31.50/A/yr. - earth ditch, siphon tubes 1
$22.50/A/yr. - concrete ditch, siphon tubes 2
$15.30/A/yr. - gafed pipe
$11.50 + $15. 30 =
Convert from 1 to 2 $31.50 - $18.90 = $12.60 = $12.50
(2) 5% clear up seep spots = $15 (see 6)
(3) Estimate $5/acre
(4) Estimate $5/acre
(5) $70/A/yr. flood irrigation 150,OOOA. = 10.5 million
$150/A/yr. furrow irrigation 300,OOOA. = 45 million
$55.5 million for 450,OOOA. = 123 = $120/A.
Sprinkler irrigation = 42 = $45
Difference is $75/A/yr.
(6) Present average value = $325/A/yr.
10% increase = 32.5 = $30/A/yr.
(7) 120 - 45 + 15 - $60/A/yr.
(8) 10% increase = $30/A/yr.
(9) 10%
(10) 10%
(11) 10%
(12) Decrease fertilizer use from 200# Ammonia NO-, to
100# = 100# saved @ 7$/16 = S7/A = $5A/yr.
(13) 5%
(14) 5%
72
-------
The final step is to find the net cost and divide
by the effectiveness factor. In some cases benefits
exceeded costs (sprinkler systems) and the final
cost minus benefit/effectiveness is a negative ^number
indicating not only can irrigation return flow quality
be improved, but also on-farm benefits will be realized.
Benefits of basin-wide improved water quality have
not been included, nor has the benefit of water
conservation for the area. These are represented
in the effectiveness factor.
Tables 3-11, 3-12, and 3-13 illustrate the result of com-
parison of effectiveness to net cost (cost-benefit). While the
analysis is based on potential on-farm costs and
benefits, other factors may influence implementation.
3.4.4 Conclusion
Sprinkler systems with or without water management
rank 1-2 for each pollutant. Labor savings of sprinklers
contributed to a net economic benefit.
Efficiency improvements (high operation and maintenance-
labor) , drainage systems, and land leveling (high
investment) rank towards the bottom.
While conveyance system improvements rank high in
controling water loss (water conservation), the cost-
effectiveness is not as high as improvements in
application systems.
This analysis serves as a comparison tool and not as
an absolute water quality model.
Areas that experience all three pollutant problems
may combine BMP's for optimum cost-benefit/effectiveness.
73
-------
TABLE 3-11. COMPARISON OF EFFECTIVENESS TO NET COST -
SALINITY
BEST
MANAGEMENT
PRACTICES
FOR SALINITY
Conveyance System
Improvements
Ditch Lining or
Pipeline
Lateral Lining
or Pipeline
Canal Lining
Sprinkler Systems
No water mgmt.
With water mgmt.
Water Management
Improvements
Efficiency
Improvements
Land Leveling
Drainage Systems
REDUCT .
EFFECT.
FACTOR
0.135
0.045
0.090
0.210
0.245
0.21
0.070
0.070
0.070
ANNUAL
COSTS/
ACRE
25
11
26
54
66
12
165
45
28
ANNUAL
BENEFIT
ACRE
25
5
5
105
90
30
30
15
15
s/ COST-BENEFIT
EFFECTIVENESS RANKII
0.
0.
-0.
-0.
-0.
1.
0.
0.
0
13
23
24
10
09
93
43
19
4
5
7
1
2
3
9
8
6
-------
TABLE 3-12. COMPARISON OF EFFECTIVENESS TO NET COST -
NITRATES
m
BEST
MANAGEMENT
PRACTICES
FOR NITRATES
Sprinkler Systems
No water mgmt.
With water mgmt.
Water management
improvements
Efficiency
improvements
Fertilizer
management
Land Leveling
Drainaae Systems
REDUCT .
EFFECT .
FACTOR
0.
0.
0.
0.
0.
0.
0.
300
350
300
100
300
050
050
ANNUAL
COSTS/
ACRE
54
66
12
165
0
45
28
ANNUAL
BENEFITS/ COST-BENEFIT
ACRE EFFECTIVENESS RANKING
105 -0.17
90 -0.07
30 -0.06
30 1.35
5 -0.02
15 0.60
15 0.26
1
2
3
7
4
6
5
-------
TABLE 3-13. COMPARISON OF EFFECTIVENESS TO NET COST -
SEDIMENT
BEST
MANAGEMENT
PRACTICES
FOR SEDIMENT
Sprinkler Systems
No water mgmt.
With water mgmt.
Water management
improvements
Efficiency
improvements
Tailwater Control
Sediment ponds
T. W. Recycling
Buffer/filter
REDUCT .
EFFECT .
FACTOR
0.855
0.855
0.450
0.450
0.630
0.630
0.315 -
ANNUAL
COSTS/
ACRE
54
66
12
165
2
58
1
ANNUAL
BENEFITS/
ACRE
105
90
30
30
0
30
0
COST- BENEFIT
EFFECTIVENESS
-0.06
-0.03
-0.04
0.30
0.01
0.04
0.01
RANKING
1
3
2
6
4
5
4
strip
Grassed
waterways
0.270
0.01
Land Leveling
0.045
45
15
0.67
-------
4.0 POLLUTANTS ASSOCIATED WITH IRRIGATION
RETURN FLOW AND THEIR EFFECTS UPON
BENEFICIAL USE
The term "pollution" means the man-made or man-induced
alteration of the chemical, physical, biological, and
radiological integrity of water (P.L. 92-500, Sec. 502-19).
When substances are present in siiffucient concentrations
(whether through man-induced or natural causes), they
may adversely affect the suitability of the water for one
or more beneficial uses.
Beneficial uses of water include the many purposes that
water serves in promoting the economic good and general
well-being of mankind. The following is a list of common
uses:
o Domestic Water Supply
o Industrial Water Supply
o Agriculture Irrigation Water Supply
o Stock and Wildlife Watering
o Propagation of Fish and Water-Contact Sprots
o Boating and Aesthetic Enjoyment
o Water Power and Navigation
States have established Water Quality Standards as maximum
allowable pollutant concentrations for various- water bodies,
These standards are generally based on beneficial uses
for the various water bodies.
The relationship of irrigated agriculture to water pollu-
tion is complicated. Some of the major polluting sub-
stances involved, such as sediments, salts, and nutrients,
are natural components of the countryside. Others are
added to the systems as a result of attempts to increase
agricultural production. These include pesticides and
fertilizers.
This chapter briefly describes the major pollutants
associated with irrigated agriculture:
o Salinity - including sodium, chlorides, and
other potentially harmful ions
o Sediment
o Nitrates
o Phosphorus
o Pesticides
o Organics
77
-------
Each pollutant is defined, and effects upon beneficial
uses are listed. The pollutant's relationship to irri-
gated agriculture is described in terms of sources and
return flow mechanisms.
4.1 SOURCES AND LOADING MECHANISMS FOR POLLUTANTS
EMANATING FROM IRRIGATED AGRICULTURE
4.1.1 Salinity
Dissolved solids, consisting of carbonates, bicarbonates,
chlorides, sulfates, phosphates, and possibly nitrates
combined with calcium, magnesium, sodium, and potassium,
are commonly referred to as salts or salinity. Salinity
levels are usually measured as Total Dissolved Solids
(TDS) or are measured indirectly as electrical conductivity.
Concentrations of the various ions involved are also
significant.
At certain concentrations, salts in the soil solution may
impair the osmotic process of water uptake by plant
roots. The degree to which plant growth is inhibited
is generally expressed in terms of the total salt concen-
tration of the soil solution. While the various ions
involved play a significant role, most data developed
to date deals with plant tolerance in terms of total dis-
solved solids or electrical conductivity. ,
Two specific ions, sodium and chloride, are of special
significance. Water with a high sodium percentage is
detrimental to soil structure. Water which is high in
chlorides may be toxic to plants. Other constituents
may also be of concern. Section 4.3.1 of this report
deals with salinity and specific ion concentrations in
terms of effect upon beneficial uses, including irrigation.
Salinity Loading Mechanisms
Salt levels in the waters of irrigated regions are pri-
marily the result of concentration resulting from consump-
tive use. All waters used for irrigation contain some
salts. As this water is used by plants (transpiration)
and evaporated from the soil, salts remain behind in the
soil water. As the salts become more concentrated, some
of the less soluble salts may precipitate. Subsequent
irrigation results in the downward movement of the soluble
salts. This leaching of salts from the root zone is
essential in terms of maintaining a favorable soil salinity.
This leaching of salts is also the primary loading
mechanism for saline return flows. Reuse of this water
results in further concentration.
78
-------
Natural Salt Load
Salts originally enter the system through three loading
mechanisms:
o Atmospheric contact;
o Weathering of rocks and soils as rainfall
and snowmelt infiltrate into the ground,
percolate through the ground, and enter
the ground water. This ground water may or
may not enter a stream;
o Weathering of rocks and soils as rainfall and
snowmelt runoff proceeds to a stream via
overland flow.
The initial salt load resulting from atmospheric contact
is negligible and unavoidable. The initial salt load
resulting from natural percolation and runoff is highly
variable depending upon local conditions. While some
streams contain high quality natural waters, other streams
are naturally high in salts.
The Effects of Irrigated Agriculture Upon Salt Load
Irrigated agriculture - the use of water for crop produc-
tion - results in increased salt concentrations in sub-
surface returns. Irrigated agriculture may or may not
result in increased salt loads. That is, the total tonnage
of salt leaving an irrigated area may be less than the
tonnage of salt entering that area.
Increased salt concentrations associated with irrigated
agriculture are the results of several factors:
o Evapo-transpiration from croplands;
o Evaporation from water bodies
o Evapo-transpiration by water loving plants
(phreatophytes) and from wet lands;
o Salt pickup from irrigation of soils which are
ither themselves saline or which overlie
saline rock or soils.
Of these factors, only salt pickup results in an increased
total salt load. All of the factors listed result in
increased salt concentrations, however. Evapo-transpiration
from croplands is the only factor which is significant
in all irrigated areas.
The fact that the overwhelming burden of salt concentra-
tion is the result of cropland evapo-transpiration poses a
distinct limitation on our ability to decrease salinity in
Western waters. Methods aimed at salinity control must
79
-------
either decrease non-beneficial consumptive use, decrease
salt pickup where it occurs, or segregate very highly-
saline return flows from returning to the system.
Evapo-transpiration from croplands is the major salt con-
centration mechanism. While the majority of this
evapo-transpiration is necessary, it is possible to reduce
some of this evapo-transpiration without reducing yield.
Reducing weed growth, changing to trickle irrigation, reduc-
tion of urban lawn watering, reduction or elimination or
irrigation of marginal lands, operation of sprinklers
only at minimal evaporation times of the day, and minimi-
zation of the number of irrigations are examples of how
evapo-transpiration from irrigated lands can be reduced
without significantly reducing yield. None of these
examples can be considered to be outstandingly effective,
however; and many are unacceptalbe within the context of
current economics, social constraints, and water availability.
Reduction of evaporation from water bodies offers marginal
possibilities at best. Evaporation losses are estimated
to be 2.8 x 1010 m3 (2.3 x 107 acre feet) annually (Lauritzen,
et.al., 1967). In some cases, canal consolidation may
be possible.
Reduction of phreatophyte use offers some possibilities for
reducing non-beneficial consumption use. In many surface
irrigated areas, canals, ditches, and lakes are run down
and lined with willows, cottonwood, and other water-loving
plants. It has been estimated that in the Western United
States, phreatophyte use is around 3.1 x 1010 m3 (2.5 x
107 acre feet) (Jensen, et.al, 1967). Much, if not most,
of this phreatophyte use occurs along natural streams and
areas of high ground water, however.
Salt pickup from irrigation of saline soils or soils over
saline rock formations occurs in only a few areas of the
West. In these areas, control measures aimed at reducing
contact may be able to show some results.
Leaching of Agricultural Soils
Continued irrigated agriculture requires maintenance of a
favorable soil salinity. This favorable soil salinity is
maintained by the application of more water than is required
to fill the root zone. This is generally not a calculated
practice. That portion of water which moves below the
bottom of the root zone is called the leaching fraction.
80
-------
LF = depth of water moving below root zone
depth of water applied plus effective rainfall
LF = Leaching Fraction
When the total amount of salts removed by the leaching
fraction equals the amount of salt applied with the irriga-
tion water, the field is said to have a salt balance. In
practice, a salt balance is often not met due to precipi-
tation of salts within the root zone. Less soluble salts
may precipitate in and below the root zone. The most
soluble salts are readily leached, however. The concept
of salt balance may be applied to a field or an irrigation
district. The salt balance is determined by an accounting
procedure.
Figure 4-1 shows a soil profile with the various inputs
and outputs of salt and water. Several computer programs
are available for modeling soil salinity and stream
loading (Hornsby 1973 and King, et.al. 1973). Hornsby
has reviewed the models and suggests that they have reached
the level of accuracy where they can be used to evaluate
changes resulting from various management practices.
The salt balance is complicated by the water and salt
storage capacity of the soil. Concentrations of salts in
the soil solution are a function of water present. As
water is removed by evapo-transpiration, stored salts become
more critical. Salinity sensors are available to monitor
soil salinity (Wesseling and Oster 1973}.
Irrigation water provides the major input of salts to the
soil profile of irrigated land. The amount of salts
added is equal to the volume of water which infiltrates
into the soil multiplied by the concentration of salts
in the water; Waters with high concentrations of dissolved
solids add a great deal of salts to the soil.
The leaching requirement (LR) is the percentage of applied
water that must be leached beyond the root zone necessary
to maintain a favorable soil solution salinity. It will
vary depending on the concentration of salts in the applied
water and the maximum allowable salinity tolerance levels
for specific crops.
Total salinity is comprised most imporantly by calcium,
magnesium, and sodium salts. Calcium and magnesium in the
proper proportions maintain soil in good condition of tilth
and structure, while the opposite is true when sodium
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EVAPOTRANSPIRATION
DEPTH
TDS-O
IRRIGATION WATER
DEPTH x TDS
EH
a
a
a
a
a
RAINFALL
DEPTH (TOS=0)
a
a
a
a
a
a
CROP
S4l $TGJ*A$E IN BOOT ZONE
LEACHATE
DEPTH x TDS
FIG. 4-1 . WATER AND SALT BALANCE
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predominates. Too much sodium causes the granular soil
structure to begin to breakdown when the soil is moistened
resulting in sealing of soil pores and a decrease in perme-
ability. Ultimately, the soil pH increases to the level
of alkali soils. Special leaching practices may be required
when sodium problems exist. The sodium problem is further
discussed in the beneficial use section.
In order to keep salt buildup to a minimum and since most
irrigators do not have the tools to calculate the LR nor
flow measuring devices, excessive amounts of water are often
applied. In addition, the LR may vary throughout a field,
and water in some irrigation systems is not applied evenly
across the field. Since water is relatively inexpensive
and nonuse may threaten the water right, the irrigator is
motivated to use more water than may be required by the
crop.
These factors result in inefficient leaching practices.
Recent research has shown some ways to make leaching more
efficient. It has been" found that the total seasonal salt
discharge from a tile drainage system was directly related
to the quantity of water discharged (King and Hanks 1975).
With small leaching fractions, the salt would be more
concentrated, but the discharge would carry less total
amounts of salt.
Frequent leaching under unsaturated soil conditions has
been shown to be more effective than under saturated
conditions (Lathin, et.al., 1969).
While the alteration of leaching practices may reduce
total salt loading, such practices can result in other
problems. Potential problems include increased salt con-
centrations for users directly dependent upon drainage water
as a water supply. In addition, alteration of leaching
practices can potentially increase the proportion of
hazardous ions.
4.1.2 Sediment
Surface irrigation, particularly furrow irrigation, is sig-
nificant in producing erosion; however, the problem is site
specific. The National Engineering Handbook on Sedimentation
comments that "...no method exists to preduct rates of waste
load transport without a substantial amount of data on
suspended concentrations during measured discharges
(USDA 1968) .
The Universal Soil Loss Equation has been used extensively
to predict soil loss from agricultural lands under rainfall
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conditions. However, it is not applicable to the conditions
encountered during irrigation. Rainfall conditions suffi-
cient to produce runoff result in an increase in flow
with distance traversed. Conversely, during the process
of surface irrigation, the flow decreases with distance.
Tests conducted in Idaho on four small fields ranging
from three to nine acres have indicated a wide range of
sediment loadings (University of Idaho 1974).
4.1.3 Nitrogen
Nitrate (NO.J , nitrogen, is a pollutant which is associated
with leaching returns from agricultural soils. The poten-
tial for nitrate leaching is greater in sandy soils. While
nitrogen may be added to the soil in many forms, soil
bacteria oxidizes these forms to the soluble nitrate form
(Figure 4-2).
?
Relationship to Irrigated Agriculture
There are several sources of nitrogen for the soil-plant
environment. Fertilizers are well known as sources, but
fertile soil itself is a pool of nutrients. Nitrogen
fixation, a process in which legume crops and micro-
organisms biologically convert atmospheric nitrogen into
usable organic nitrogen, is another common source. Preci-
pitation picks up nitrogen. Animal wastes and plant resi-
dues also provide inexpensive nitrogen to the soil. Relative
contributions vary considerably.
Fertilizers add nitrogen to the soil. Examples of chemical
fertilizers are Ammonium Sulfate (NH4)2 S04, Ammonium
Nitrate NH4NO , Urea CO(NH2)9, and Anhydrous Ammonia liquid
NH3. J ^
The ammonium fertilizer divides into four pathways. Soil
organisms absorb a considerable portion of the ammonium.
Second, higher plants are capable of using this form of
nitrogen, especially young plants. Third, NH4 may be fixed
by clay, minerals, and organic matter. In this form, it
is not readily available, but is subject to slow release.
Finally, the remaining NH4 is subject to nitrification,
resulitng in Nitrate (NO ).
The nitrogen contained in soil organisms is not considered
to be readily available to the plant, nor is it mobile
within the soil. This nitrogen is not lost, however, as
it is subject to slow release as organisms decay. Ammonium
adsorbed on soil particles is not particularly mobile
within the soil. Ammonium is also unstable in the soil
system.
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N-FIXATION
GASEOUS LOSS
LOSS
RESIDUES,
MANURES
and WASTES
DRAINAGE
LOSS
FIGURE 4-2 THE NITROGEN CYCLE
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Under well-aerated conditions, nitrification is complete
within a few feet of the soil surface (Pruvel 1968) .
Nitrate (NC>3) is highly soluble in water and highly mobile
and has been shown to move with the wetting front (Edward,
et.al., 1972). These factors are the reason why nitrates
are readily leached.
Leaching losses of nitrate represent an economic loss
to the farmer as well as an environmentel pollutant
source. As a result, slow release fertilizers which nitrify
slowly are preferable. Methods of achieving slow release
include coating the fertilizer pellets and adding
chemicals to inhibit nitrification. Recent research
has indicated that ammonium is available to plants,
especially young plants. This provides further motivation
inhibiting nitrification. Urea is a relatively slow release
fertilizer which is now in common use. Manure is also a
slow release nitrogen source.
Since seepage is the major export pathway, irrigation water
use plays a major role in nitrate loss. Balton, Aylesworth,
et.al, found that the amount of water percolated through
the root zone had a direct effect on nitrate loading.
Increased fertilizer use will not necessarily increase
nitrate loading unless a significant leaching fraction is
applied or the ability of the crop to take up nitrogen is
exceeded. Erickson and Ellis and Hendrick and Letey (1975)
did not find a correlation between fertilizer use and seep-
age loss of nitrates. On the other hand, Broadbent and
Chapman found a definite correlation. These results indicate
that crops and soils play a significant role.
Fertilizer loss 4n runoff is dependent upon application and
management (Timmons, et.al., 1973). Incorporation of
nitrogen by plowing or discing after application will
reduce runoff losses.
As in seepage losses of nitrogen, fertlizer use does not
necessarily determine the amount of surface losses.
Uttormark (1974) cites two studies to this effect. Soil
type can have a great influence on surface losses (Sievens
1970) as can water flow (Taylor, et.al.).
Sometimes fertilizers are added to and applied with irri-
gation water. Since nitrates are highly soluble in
water, bypass water and tailwater can transport to receiving
streams, if not managed properly.
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4.1.4 Phosphorus
Phosphorus does not occur free in nature but is found
in the form of phosphates. Phosphates contained in sur-
face waters or groundwaters are sometimes the result of
leaching of minerals or ores, natural processes of degrada-
tion, agricultural returns, industrial wastes, discharge
of cooling waters containing phosphates, decomposition or
organic matter, and discharge of municipal wastewaters.
In the United States, 76 percent of the total phosphorus
use is by agriculture (Kramer, et.al., 1972). Agriculture
is probably responsible for a lesser proportion of the
phosphorus loading to streams due to the nature of phos-
phorus in soils. Estimates of phosphorus loading vary
significantly from 0.5 to 4.5 kg/hectare/year (0.4 to 4.0
pounds/acre/year) (Task Group 1967) and 0.003 to 1.1 kg/
hectare/year (0.003 to 1.0 pounds/acre/year) (State of
Illinois, 1972). These statistics indicate the phosphorus
loading is extremely variable and highly dependent on
locatlized conditions.
Phosphorus is naturally present in the soil environment
and can be added by application of fertilizers, animal
wastes, plant residues, and precipitation. The chemistry
of phosphorus in soils results in the existence of both
inorganic and organic forms of phosphorus. The available
soil phosphorus can be lost through crop removal, fixation,
leaching losses, and erosion losses. Figure 4-3 shows
the pathways of fertilizer phosphorus and Figure 4-4
describes the phosphorus cycle in agriculture.
Commercial fertlizers commonly add inorganic phosphorus
compounds to the soil. Ortho-phosphate ions have a great
affinity for various cations inthe soil: CA+ , Fe+3,
Zn+2, A+3. In alkaline soils, compounds of calcium
predominate. Of the phosphorus added as fertilizer, most
is fixed to the soil in this manner. These inorganic
phosphorus compounds are slightly soluble although a small
portion of the fixed phosphorus may become available with
time. The availability of this inorganic phosphorus is
a function of pH, with maximum availabilitiy between pH
5.5 and 7.0 (Buckman and Brady, 1969). In the alkaline
soils of the West, availability is quite low since the
calcium-phosphates are not very soluble.
The ability of soils to fix phosphorus in inroganic com-
pounds is enormous. A study of Mexico silt load indi-
cated that two plots had similar ability to absorb phosphates
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CROP RESIDUES
AND MANURES
COMMERCIAL
FERTILIZERS
PHOS. BEARING
SOIL MINERALS
k
*
[Major pathways (heavy lines) are fixation and crop removal.]
FIG. 4-3- PATHWAYS OF FERTILIZER PHOSPHORUS
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MINING
DUST
BY
PRECIPITATION
DESORPTION
MINERALIZATION
FIG. 4-4. THE PHOSPHORUS CYCLE IN AGRICULTURE
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where one of the plots had received phosphate fertiliza-
tion for 82 years and the other was fertilized for the
first time (Kao and Blancher, 1973).
Phosphorus in Surface Runoff
Surface runoff is the major source of phosphorus loss from
agricultural lands. Phosphorus is associated with sedi-
ment due to the ionic combinations it forms with soil
particles. Both inorganic and organic phosphorus are
picked up in the erosion process. The organic materials
are especially susceptible due to the low density of organic
matter.
Loadings of phosphates in surface runoff are reported by
Uttorraark (1974) and Porcella (1974) for the several
studies which have been conducted. The loadings vary over
several orders of magnitude.
Drainage Losses of Phosphorus
Because of the low solution concentrations and high degree
of adsorption, phosphate is not readily leached.
4.1.5 Pesticides
Pesticides are substances used during production, storage,
and transportation of food for the purpose of preventing
or destroying insects, weeds, rodents, or fungi. In
irrigated agriculture, pesticides include herbicides,
insecticides, and fungicides. Figure 4-5 shows pesticide
cycling in the environment.
Agricultural benefits of pesticides include: 1) promotion
of higher crop yields; 2) improved quality of produce; and
3) reduced cultivation requirements. These benefits have
resulted in economic benefits to the farmer and the consumer,
Insecticides, herbicides, and fungicides will continue to
be used if our level of agricultural production is to be
maintained or increased.
Some pesticides have a great affinity for soil particles
and organic material and as a result are transported
with sediment. Others are highly soluble and subject to
transport to leachate and as the soluble portion of runoff.
The Soil Conservation Service (SCS) has categorized 171
agricultural pesticides according to the mode of transport.
The results are summarized below:
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PESTICIDE APPLIED
Degradation
loss
SPRAY GRANULES
PELLETS. FUMIGANTS
Injection,
soil incorpation
Injection
pellets, etc
Degradation loss
Interception
Volatility
Codistillation ,
1- *
Codistillation,
Wind
Spill age
Accident
Volatilty
Codisti llation
Accidents
i
Industry
Sewage
Indust ry
Sewage
Decay Exudatic
_ \ [ Absorption. Irrigation
Excretion » —Adsorption
AQUATIC
ORGANISM
Degradation loss
Degradation loss
FIG. 4-5. PESTICIDE CYCLING IN THE ENVIRONMENT [A]
[A] HYOROCOMP
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Predominant Percent
Transport Mechanism of Sample
Associated with Sediment 46
Associated with Water 30
Associated with Sediment
and Water 16
Unknown 8
TOTAL 100
4.1.6 Other Pollutants
Disease-producing organisms (bacteria) and organics are
rarely irrigation-caused pollutants.
Bacteria
Some bacteria cause disease in higher animals. The
presence of fecal coliform bacteria indicates mammal fecal
contamination. Fecal streptococcus bacteria are indicators
of grazing animal fecal contamination.
The soil itself contains many bacteria which perform a
variety of necessary functions. These bacteria would not
be indicated in a fecal bacteria test.
Studies of the occurrence of coliform bacteria in drainage
water have shown that irrigation drainages does not exert
a bacterial pollution load. Studies in Idaho have indicated
that irrigation drainage water may be of improved bacteri-
ological quality compared to irrigation water which was
consistently polluted with fecal bacteria (Smith, et.al.,
1972). Another study by the same authors failed to find
similar results (Smith and Douglas, 1973). In this study,
fecal concentrations were similar in irrigation and drain-
age waters. It was still concluded that irrigation has
minimum deleterious effects on the microbiological quality
of water.
Bacterial contamination of surface runoff from irrigated
cropland has received less attention than drainage water.
Surface runoff would not be suspect as a bacterial pollu-
tion source except where surface runoff occurred after
application of manure which had not yet been incorporated
into the soil. In these cases, tailwater or rainfall runoff
could erode significant quantities of manure causing a sig-
nificant bacterial pollution load.
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Organics
Organic pollution is associated with crop residue, manure,
or humus being lost from the cropland. The subsequent
biological oxidation of this organic matter could place
an oxygen demand upon the stream. Studies of runoff
exerting a biochemical oxygen demand (BOD) have been
conducted in the dairy states where manure is applied to
frozen ground over the winter in areas with a large spring
runoff. These conditions would not be expected to exist
in most irrigated regions.
The soil has the capacity to act similar to the trickling
filter used in sewage treatement. Bacteria attached to
the soil would oxidize most organic matter to C02 during
its flow through the soil.
Surface runoff or tailwater would be expected to exert a
large BOD where runoff occurred from land having manure
applied, but not incorporated into the soil. This would
be considered to be a rare case, however, as manure is
usually plowed in before such events occur.
Temperature
Surface returns from irrigated agriculture may be of
increased temperature. Drainage returns would be expected
to arrive at soil temperature. Very little work has been
done on the increased temperature resulting from irrigation.
4.2 IDENTIFICATION OF WATER QUALITY PROBLEMS ASSOCIATED
WITH IRRIGATED AGRICULTURE
Best management practices for irrigated agriculture must
be considered in terms of both agricultural practices and
local and regional water quality problems. This section
presents some information on the relationship between
irrigation return flows and water quality problems.
4.2.1 Locating Return Flows
Return flows must be defined in terms of location and quan-
tity. The quality of return flows is equally important
and discussed in the next section.
Each irrigated area has its own relationship between water
supply, water application method, return flow, and receiving
water/ Water supply may be either:
o Surface water;
o Well water.
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Water application methods may be:
o Furrow
o Border
o Dead level
o Wild flooding
o Sprinkler
o Trickle.
There are five basic irrigation return flows in irrigated
agriculture:
o Canal seepage
o Bypass water
o Sursurface articifical drainage
o Deep percolation
o Tailwater.
These return flows may impact either:
o Surface water
o Ground water.
Returns which initially impact ground water may end up
in surface waters.
Surface return flows can be located and quantified more
easily than subsurface flows. Canal seepage and deep
percolation return flows can be most readily located by
quantifying inflows and outflows which can be located.
There are three basic methods for determining the quantity
of return flows to a river.
The first method is by consultation with the River Commis-
sioner. As part of the day-to-day job of scheduling diver-
sions, the River Commissioner usually knows where return
flows are occurring, and the amounts of seepage and
tributary inflows.
A second way is by an inflow-outflow analysis conducted
between two points of known flow on the river. By adding
tributary inflows and discharges to the river to the upstream
known flow, subtracting outflows and diversions from the
upstream known flow, and comparing the result with the
downstream known flow, the amount gained or lost through
seepage can be estimated. If the resultant flow and known
flow are equal, a water quality analysis must be performed
to determine whether there is an unaccounted pollutant load
on the river. If there is, some nonpoint return flow may
be reaching the river, while an equivalent amount of river
water is lost through seepage or phreatophyte usage.
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The third method is by on-site investigations and measure-
ments. Actual measurement of return flow quantities can be
taken by flow measurement devices. Seepage inflows may
be estimated by taking flow measurements at two points on
the river where there are no other outflows or inflows
between the points.
Figure 4-6 diagrams a return flow system. While this is
a common system, it does not represent all systems. Analysis
of each system will require determination of inflows,
outflows, and pathways. Determination of these pathways
combined with quality analysis of returns and receiving
waters is central to understanding and dealing with water
quality problems in irrigated areas.
4.2.2 Determination of Return Flow Quality and Quantity
The existence of practices and conditions which result in
irrigation return flow does not mean that there are definite
water quality problems. The existence of water quality
problems may be proven by water quality data already
collected. In many cases, however, much more detailed data
is necessary. In addition, the water quality data must
be correlated to irrigated agriculture return flows.
Monitoring Program
A monitoring program to identify water quality problems
should be undertaken at both the on-farm and subregional
levels. An on-farm program will involve:
o Flow measurements of irrigation water;
o Flow measurements of return flows;
o Sampling for irrigation water quality;
o Sampling for return flow quality.
Flow measurements and sampling should take place at the
same sites in order to calculate both the quantity of
pollutant and the concentration. Concentrations have
weight per volume units and can be multiplied by the volume
of water to obtain a total pollutant load. Total weight
can be more meaningful to a program than concentrations.
A monitoring program at a subregional level would identify
water quality problems in the river, or ground water
aquifer, and ultimately relate those problems to irrigation
return flows. This program will entail:
o Flow measurements of the river;
o Sampling for river water quality;
o Sampling for ground water quality;
o Diversion records;
o Tributary inflow.
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ARTIFICIA
VSUBSURFA
DRAINAG
FIG. 4-6. IRRIGATED AGRICULTURE RETURN FLOWS
(SURFACE SUPPLY AND RETURN SYSTEM)
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Here again, sampling locations and flow measurement go
hand in hand.
An irrigation return flow monitoring program requires
selection of sampling and measurement sites, sampling
procedures, selection of pollutant parameters, and flow
measurement techniques.
Sampling and Measurement Site Selection. Site selec-
tion should be based on frequency of data collection,
accessibility, good representative samples and measurements,
and adequate study area coverage. Samples and measurements
will be collected on a regular schedule for some sites
and not others. Schedules are dependent on irrigation
scheduling and river diversion schedules. Irrigation wells,
points of diversion, reservoir outlets, head ditches,
drainage outfalls, and return flow ditches are examples of
monitoring locations. Ground water samples may require
boring and casing of a sampling well at selected locations
in the irrigation area.
Sampling Procedures. The following items are essential
for good results in a sampling program:
o Samples should be taken at locations where
the water is well mixed;
o Large-mouth glass or plastic jars should be
used;
o Sufficient volume should be collected to allow
re-run of some analyses, if necessary.
Important Pollutant Parameters
In order to carry out a monitoring program it is important
to have a general understanding of parameter analyses.
The major parameters of concern in an irrigation return
flow study are salinity, sediment, nitrogen, phosphorus,
and pesticides. Major pollutant pathways (Figure 4-2)
will dictate locations of monitoring stations. Other water
quality parameters such as dissolved oxygen (DO), biochemical
oxygen demand (BOD) , and pH are good indicators of pollution
problems in general. For more detailed discussions of
parameter analyses, refer to Standard Methods for the
Examination of Water and Wastewater (most current edition)
and/or Manual of Methods for Chemical Analysis of Water and
Wastes (U.S. Environmental Protection Agency, current
edition).
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Salinity. Salinity may be measured as total dissolved
solids or electrical conductivity. Both measurements
are acceptable, and it is desirable to measure both in at
least the initial stages of a program. Measurement of
salinity by both methods allows a check, and may often
be used to develop a correlation between the two measure-
ments. More intense study of salinity may focus on speci-
fic caitons and anions.
The cations are calcium (Ca), magnesium (Mg), potassium
(K), and sodium (Na). The relative concentrations of these
ions is indicative of possible sodium hazards.
Total dissolved solids is the weight of the residue from
a filtered sample after evaporation. Filtration removes
suspended matter, and a 40-micron membrane filter is often
used; although other sizes may also be used where they fit
the circumstances. Drying temperatures of 103°C, or
179-181°C, are used depending upon what is to be measured.
Residues dried at 179-181°C generally yield values of
dissolved solids most close to that obtained by summation
of the various constituents (weight of cations plus weight
of anions, Standard Methods). This temperature is recommended
for analysis of irrigation return flow.
Total dissolved solids may also be determined by summation
of cations and anions. This is an excellent method when
full analysis is called for.
Specific conductance yields a measure of a water's
capacity to convey an electric current. The conductance
of a water is related to the total concentration of
ionized substances. The relationship between specific
conductance and total dissolved solids is dependent upon
the cations and anions involved. The conductance is also
dependent upon temperature.
Sediment. Since sediment is due to erosion processes
during irrigation and is highly variable in the context of
flowing streams, it is hard to quantify. Sediment concen-
trations can be measured in tailwater flows by analyzing
the sample for suspended solids. Tailwater detention
ponds can be measured for sediment prior to and after
irrigation season to get an estimate of sediment yield.
Suspended solids in a measured volume of sample are collected
on a weighed glass fiber pad, dried at 103-105°C, and re-
weighed. The amount required for analysis is 100 ml.
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Nitrogen. Nitrates are the primary form of nitro-
gen occurring in return flows and in ground waters.
Ground water concentrations of nitrates will usually be
much higher than surface waters, because of the absence
of plants and photosynthesis. As the decomposition
process progresses, organic nitrogen is converted to
ammonia, and further to nitrite and nitrate. Also,
ammonia nitrogen is often added as fertilizer. Therefore,
in some cases, other forms of nitrogen should be examined.
Samples for nitrogen forms should be analyzed as soon
as possible after collection to avoid loss due to biolog-
ical activity. These samples should be cooled to 4°C
and analyzed within 24 hours. If this is not possible,
preservative measures can be taken. At least 25 ml
of sample is required to test for nitrate as N.
Phosphorus. The level of effort directed to phos-
phorus study will be determined by the extent of existing
or anticipated algae problems in downstream rivers and
lakes. Phosphorus has an affinity for soil particles
and is associated more with tailwater than drainage water.
The attached phosphorus is not readily available to algae
and yet it may become available if other forms of phos-
phorus are not available. This would be the situation
only in the most pure waters. Generally, the ortho-
phosphate group is the only form available. As a result,
it is recommended that ortho-phosphates be tested for in
irrigation return flow studies. In addition, total
phosphorus should be tested for where it may become necessary
to have this data in later eutrophication studies. Fifty
milliliters is the amount required for analysis.
Pesticides. Due to the very low levels usually pre-
sent in stream samples and uncertainty as to what levels are
significant, a relatively large sample is required for
analysis in most surface water. If necessary, any clean
glass or metal (avoid plastic) container or combination of
containers totalling one-half gallon capacity or more may
be used. At least 1,000 ml are required for analysis.
In order to test for particular pesticides, it is beneficial
to find out which pesticides are predominantly used in
an area. Pesticide analyses are expensive and should not
be wasted.
Laboratory Analysis. Laboratory equipment is expen-
sive; thus, it is advantageous to have samples analyzed by
existing laboratories.
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o Consulting engineering firms, environmental
testing labs, and other testing labs hire out
their services;
o Large cities usually have well-equipped lab-
oratories and trained personnel;
o Some industries hire out their personnel and
lab facilities, on the side, to do testing work;
o Universities generally have facilities and
trained personnel.
Flow Measurement. Flow measurements should be taken
at the same locations and times that water quality samples
are taken. The U.S. Department of Interior, Bureau of
Reclamation, has published a handbook detailing flow mea-
surements entitled, Water Measurement Manual.
V-notch weirs, built to standard dimensions can be used
to estimate flows. Parshall flumes are also available.
These devices are not very portable and should be installed
for an entire season. Conversion tables are used to give
actual flow values. Recorders may be fitted to these devices,
Volumetric methods (bucket and stopwatch method) are
excellent for measuring small flows from pipes.
Flows from wells may be closely estimated, using the
California pipe method explained in the Water Measurement
Manual.
A final method is to use flow meters, which can determine
velocity in open channels..
4.2.3 Analysis of the Water Quality Impacts of Irrigation
Returns
Evaluation of the water quality impacts of return flows
must take into consideration:
o Irrigation hydrology;
o Quality of supply water, return flows, and
in-stream flow;
o Agricultural practices;
o Natural conditions;
o Downstream water uses.
These factors may then be used to define pollutant prob-
lems in an irrigated region.
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Irrigation hydrology is important since it is the system
of diversions and returns that causes the degradation of
many Western waters. Some of this degradation is the
necessary and direct result of consumptive use concen-
trating salts. Unnecessary salt pickup and the return of
other pollutants is the result of inefficiencies in the
irrigation system, however.
Water quality of return flows should be considered in
terms of the impact they have upon the stream. This
means knowing the stream water quality, as well as the
quality of the return flow. Particular attention should
be paid to the quality of a return flow as it relates to
agricultural practices and natural conditions.
Analysis of Parameters Associated with Leaching.
Salinity and nitrate concentrations may increase as a
result of the inflow of lower quality seep or tributary
inflows. Base level salinity increases resulting from
consumptive use should be analyzed. Locating areas
contributing high pollutant loads may be used to define
potential problem areas. Figures 4-7 and 4-8 show analyses
of data for water quality and correlation to mapped data.
Analysis of Parameters Associated with Surface Runoff
Surface runoff carries sediment and phosphorus as well as
some pesticides. Since sediment and phosphorus are carried
by surface returns, tributary inflow should be the only
source of these pollutants. Some problems occur with
analysis of sediment and phosphorus since these constituents
are not dissolved and thus, are not conservative. In
addition, it may be that a program does not locate all
sources.
Sediment may settle out in the stream, or be picked up
from stream bottom sediment left during a low flow period.
Bank erosion may be a significant sediment source during
high flow periods.
Phosphorus associated with irrigation tailwater tends to be
attached to soil particles. As a result, it is subject to
settling and pickup in much the same way as sediment.
Computer Simulation of Irrigation Return Flow
The U.S. Bureau of Reclamation has developed a computer
model for simulating subsurface irrigation return flows.
The benefits to be derived from using such a model are
obvious. If a system can be modeled with sufficient
101
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yZ. < =•. I NON-IRRIGATED
SOILS WITH SALINITY HAZARD
V/////A SOILS WITH EROSION HAZARD
j CANALS
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corporation
(ov«land. eo.
FIG. 4 7. CORRELATION OF MAPPED DATA
102
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I. I •
DIVERSIONS
(cfs)
TRIBUTARIES
(cfs)
r IT
T
10
~o RIVER
MILE
MAJOR
SUBSURFACE
DRAINS (cfs)
ESTIMATED
SEEP (cfs)
too
FLOW
(cfs)
2OOO 1
TDS
IN RIVER
TDS
RETURNS
(mg/l)
IN STREAM
(mg/l)
MAJOR DRAINS
SS
(mg/l)
IN STREAM
SS
(mg/l)
TRIBUTARIES
SCO •
Ml!
FIG. 4-8, WATER QUALITY ANALYSIS
103
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lovvland, co.
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accuracy, input parameters can be adjusted for changes in
practice to predict water quality improvements. The
model is quite sophisticated and can simulate chemical
changes, as well as hydrologic loading.
While the model represents the state of the art, some
limitations exist on its use and accuracy. As with any
model, it is a simplification of very complex, natural
processes. Such natural processes are very hard to simu-
late. Tremendous amounts of time and money can be spent
in calibration. Input data requirements are quite high.
Even with a high degree of effort, confidence in predicted
results may be low, andlpredicted results may be exceedingly
sensitive to an input which cannot be precisely quantified.
Costs associated with collecting input data for a model,
calibration, sensitivity analysis, etc., may be enormous.
These costs may exceed the cost involved in demonstration
projects, with much less confidence in the accuracy of
results.
Evaluation of Pollutant Problems Associated with
Return Flow in Terms of Potential Benficial Use Downstream
Pollutant problems should be evaluated in terms of down-
stream water use if a water quality benefit is to be
realized. For this reason, both existing and potential
uses of downstream water should be evaluated. Local stream
standards should also be taken into consideration.
4.3 WATER QUALITY REQUIREMENTS FOR BENFICIAL USES
Water pollution emanating from irrigated agriculture
may degrade the quality of water for one or more benefi-
cial uses, including:
o Irrigation
o Livestock water;
o Domestic supply;
o Fishing;
o Recreation.
The value of reducing the irrigation return flow pollution
load lies in the improvement of quality for one of these
uses. It is often not possible to place a dollar value
on expected improvements, however. Water quality standards
are generally established through consideration of beneficial
use aspects.
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4.3.1. Irrigation Water
Salinity. Dissolved solids are the pollutants of
major concern in irrigation waters. The various cations
and anions increase osmotic pressure. In the soil
solution, water may contain five to ten times the salinity
of irrigation water. High osmotic pressure of the soil
solution can result in reduced yields or the requirements
to grow tolerant crops.
The degree of harm caused by various salinity levels and
by various ion concentrations is highly dependent upon
crop, soil, and management practices. Irrigation waters
may be classified according to the diagram presented in
Figure 4-9. The suitability of these waters for various
crops and soils is presented in Table 4-1. It should be
noted that the information presented represents guide-
lines and that in practice waters of poorer quality are
often used. The use of these lower quality waters may
come at the expense of reduced yields, increased management
requirements, or salt buildup in the soil, however.
Relative salt tolerance for several crops is displayed
in Table 4-2. It should be noted that the table is based
on the conductivity of the soil moisture extract which
may easily be five times the conductivity of applied
water, due to the concentration of salts resulting from
consumptive use. It should also be noted that the table
displays only relative tolerance, and that in practice
soil moisture salinity may exceed these levels. Compre-
hensive up-to-date information on crop tolerance to salinity
is presented by Maas and Hoffman (1977), Ayers (1977),
and Christiansen, Olsen, and Willardson (1977).
\
Sodium. The most common method displaying the
relative sodium hazard is the Sodium Adsorption Ratio
(SAR) :
SAR = Na
/
Ca++ + Mg'
2
where NaT, Ca++, and Mg"1"1" are expressed in me/1.
The SAR may be used to determine the quality of water for
irrigation as is displayed in Table 4-1.
Sodium problems mainly occur in soil structure, infil-
tration, and permiability rates. These problems are
especially pronounced on clays, especially swelling
clays.
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WATER QUALITY CRITERIA
100
4 SOOO
IOO ISO 7SO 2250
CONDUCTIVITY - MICROMHOS/CM AT 25°C
SALINITY HAZARD
FIG. 4-9. DIAGRAM FOR THE CLASSIFICATION OF
IRRIGATION WATERS CAH
CAD USDA, 1954
J.UD
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TABLE 4-1 SUITABILITY OF WATERS FOR IRRIGATION*
Class
Salinity or
Conductivity
Sodium-Adsorption
Ratio+
Low Low-Salinity Water (Cl) can be
1 used for irrigation with most
crops on most soils with little
likelihood that soil salinity
will develop. Some leaching is
required, but this occurs under
normal irrigation practices ex-
cept in soils of extremely low
permeability.
Low-Sodium Water (SI) can be used
for irrigation of almost all
sails with little danger of the
development of harmful levels of
exchangeable sodium. However,
sodium-sensitive crops such as
stone fruit trees and avocados
may accumulate injurious concen-
trations of sodium.
Medium Medium-Salinity Water (C2) can
2 be used if a moderate amount of
leaching occurs. Plants with
moderate salt tolerance can be
grown in most cases without
special practices for salinity
control.
Medium-Sodium Water (S2) will pre-
sent an appreciable sodium hazard
in fine-textured soils having
high cation-exchange capacity, es-
pecially under low-leaching condi-
tions, unless gypsum is present
in the soil. This water may be
used on coarse-textured or organic
soils with good permeability.
High High-Salinity Water (C3) cannot
3 be used on soils with restricted
damage. Even with adequate drain-
age, special management for
salinity control may be required
and plants with good salt toler-
ance should be selected.
High-Sodium S3) may produce harm-
ful levels of exchangeable sodium
•in most soils and will require
special soil management-good
drainage, high leaching, and
organic matter additions. Gypsif-
erous soils may not develop harm-
ful levels of exchangeable sodium
from such waters. Chemical amend-
ments may be required for replace-
ment of exchangeable sodium, ex-
cept that amendments may not be
feasible with waters of very high
salinity.
Very Very High Salinity Water (C4)
High is not suitable for irrigation
4 under ordinary conditions, but
may be used occasionally under
very special circumstances.
The soils must be permeable,
drainage must be adequate, irri-
gation water must be applied in
excess to provide considerable
leaching, and very salt-toler-
ant crops should be selected.
Very High Sodium Water (S4) is gen-
erally unsatisfactory for irriga-
tion purposes except at low and
perhaps medium salinity, where the
solution of calcium from the soil
or use of gypsum or other amendments
may make the use of these waters
feasible.
Adapted from U.S.D.A., 1954. .
Sometimes the irrigation water may dissolve sufficient calcium from
calcareous soils to decrease the sodium hazard appreciably, and this
should be taken into account in the use of C1-S3 and C1-S4 waters.
For calcareous soils with'high pll values or for noncalcareous soils,
the sodium status of waters in classes C1-S3, C1-S4, and C2-S4 may
be improved by the addition of gypsum to the water. Similarly, it
may be beneficial to add gypsum to the soil periodically when C2-S3
and C3-S2 waters are used.
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TABLE 4-2 RELATIVE SALT TOLERANCE OF
VARIOUS CROP PLANTS (a)
Relatively
Nontolerant
EC x 103
2.0-4.0(b)
Field beans
Cowpeas
White clover
Alsike clover
Red clover
Ladino clover
Crimson clover
Rose clover
Burnet clover
Lima bean
Green bean
Cel ery
Radish
Pear
Apple
Orange
Grapefruit
Plum
Apricot
Peach
Strawberry
Lemon
Avocado
Moderately Relatively
Salt Tolerant Salt Tolerant
EC x 103 EC x 103
4.0-6. 0(b) 6.0-8'.0(b)
FIELD CROPS
Sorghum(grain) Cotton
Corn(field) Rye(grain)
Castorbean Wheat(grain)
Soybean Oats(grain)
Rice
FORAGE CROPS
Tall fescue Wheat-grasses
Meadow fescue Sudan grass
Orchard-grass Sweetclover
Millet Alfalfa
Sour clover Ryegrass
Birdsfoot trefoil Rye (hay)
Wheat (hay)
Oats (hay)
VEGETABLE CROPS
Tomato Garden beet
Broccoli Kale
Cabbage Spinach
Pepper Okra
Lettuce
Sweet corn
Onion
Pea
Watermelon
Cantaloupe
Squash
FRUIT CROPS
Olive Pomegranate
Grape Fig
Highly
Salt Tolerant
EC x 103
8. 0-12. Kb)
Barley(grain)
Sugar Beet
Rape
Alkali sacaton
Bermuda grass
Barley(hay)
Rhodesgrass
Blue grama
Panicgrass
Asparagus
Date Palm
.
(b) Conductivity of saturation extract from the soil
mi 1 1 i -mhos/em at 25°C.
expressed as
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Where sodium problems exist, calcium, calcium producing
amendments, sulfur, or acids may be added to the soil
in an effort to exchange calcium for sodium in the soil and
leach sodium from the root zone.
Chlorides. Chlorides may be harmful to certain crops.
Particularly sensitive are fruit crops - citrus, avocado,
grapes, and certain berries. Detriment to these crops may
occur through either chloride levels in the soil or
foliar absorption of sprinkler-applied water. Chloride
tolerance is highly variable upon crop type.
Chlorides are the most soluble anion. While others may
precipitate in the soil, chlorides tend to remain in the
system and concentrate proportional to water useage.
Sediment
The effect of sediment is highly dependent upon irrigation
method. Sediment is detrimental for sprinkler or trickle
irrigation since it may cause clogging and wear. Fine
sediment may be benficial for surface irrigation of sandy
soils, since the fines trapped in the sand can reduce
infiltration making the water advance down the furrow
faster.
Nitrates. Nitrates are generally beneficial in
irrigation water.
Phosphorus. Phosphorus is beneficial in water to be
used for irrigation.
Pesticides. Pesticides are detrimental to water to
be used for irrigation.
4.3.2 Livestock Water
Dissolved Solids
The quality of water required for livestock is dependent
upon the type of animal -and the acclimatization of the
animal to water of a particular dissolved solids level.
Dissolved solids in livestock water are primarily detri-
mental because they impair the osmotic process. General
guidelines for livestock water are presented in Table 4 3.
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TABLE 4-3 GUIDE TO THE USE OP
SALINE WATERS FOR LIVESTOCK
AND POULTRY
(Committee on Water Quality Criteria 1972)
Total Soluble Salt
Content of Waters
(mg/1) Comment
Less than 1,000
1,000-2,999
3,000-4,999
5,000-6,999
7,000-10,000
Over 10,000
Relatively low level of salinity.
Excellent for all classes of live-
stock and poultry.
Very satisfactory for all classes of
livestock and poultry. May cause
temporary and mild diarrhea in live-
stock not accustomed to them or watery
droppings in poultry.
Satisfactory for livestock, but may
cause temporary diarrhea or be
refused at first by animals not
accustomed to them. Poor waters for
poultry, often causing water feces,
increased mortality, and decreased
growth, especially in turkeys.
Can be used with reasonable safety
for dairy and beef cattle, for sheep,
swine, and horses. Avoid use for
pregnant or lactating animals. Not
acceptable for poultry.
Unfit for poultry and probably for
swine. Considerable risk in using
for pregnant or lactating cows, horses,
or sheep, or for the young of these
species. In general, use should be
avoided although older ruminants,
horses, poultry, and swine may sub-
sist on them under certain conditions.
Risks with these highly saline waters
are so great that they cannot be
recommended for use under any condi-
tions.
Nitrates and Nitrites
Nitrate and nitrite may cause poisoning of livestock. The
Committee on Water Quality (1972) has recommended that
110
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NCU-N plus NO -N content in drinking waters for livestock
and poultry should be limited to 100 mg/1 or less, and the
N02-N content should be limited to 10 mg/1 or less.
Pesticides
While there were no reported cases of livestock toxicity
resulting from pesticides in water, a potential problem
exists (Committee on Water Quality Criteria, EPA, 1972).
4.3.3 Domestic Use
Several physical (aesthetic), chemical, and bacteriological
standards are placed on water for domestic supply. Irri-
gation return flows and receiving waters may not meet
these standards because of diminished physical and chemi-
cal quality. Table 4-4 displays recommended and manda-
tory limits for many constituents.
Physical parameters impairing water quality are turbidity
and odor. These properties are generally treated in conven-
tional water treatment. Surface irrigation systems which
return tailwater to the river can increase turbidity in
the river.
Chemical characteristics of drinking water must meet many
criteria in order to be considered good. Needless to say,
many water supplies do not meet recommended limits.
Various cations and anions associated with irrigation return
flows, as well as total dissolved solids levels, have
either recommended limits or mandatory limits.
Total dissolved solids levels increase as a result of
irrigation. There are no mandatory limits for total
dissolved solids, since low TDS waters are totally un-
avoidable in many areas. Dissolved solids are primarily
an impairment to taste, although sodium may be detrimental
to those who are on restricted sodium ditets.
Nitrates plus nitrites are limited to 10 mg/1 as N in the
EPA Interim Primary Water Standards. This has been estab-
lished as a safe amount. Levels above this have been
linked to methemoglobinemia in infants.
Irrigation leachate can be of significantly higher nitrate
concentrations than applied water. Although returns of
seepage water rarely cause surface water to contain more
than 10 mg/1 N03-N+NO2-N, ground water may contain this
much or more. Irrigation returns may contribute to the
loading of high nitrate waters to the ground water,
especially when large amounts of fertilizer are used on
sandy soils.
Ill
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TABLE 4-4 EPA WATER QUALITY STANDARDS FOR DISCHARGE TO GROUND
WATERS UTILIZED AS A DRINKING WATER SUPPLY
Maximum Allowable Level (a)
National Interim Proposed National
Primary Drinking Secondary Drinking
Constituent Water Standards Water Standards
Chemical
Arsenic (As)
Barium (Ba)
Chloride (Cl)
Chromium (Cr)
Copper (Cu)
Fluoride (F)
53.8QF
58.4-58.3
63.9-70.6
70.7-79.2
79.3-90.5
Foaming Agents (MBAS)
Hydrogen Ion (pH)(b)
Hydrogen Sulfide (H2S)
Iron (Fe)
Lead (Pb)
Manganese (Mn)
Mercury (Hg)
Nitrate (N03 as N)
Selenium (Se)
Silver (Ag)
Total Dissolved Solids (TDS)
Zinc (Zn)
0.05
1.0
-
0.05
-
2.4
2.2
1.8
1.6
1.4
-
-
-
-
0.05
-
0.002
10.0
0.01
0,05
_
—
-
-
250.
-
1
-
-
-
-
-
0.05
6.5-8.5(f)
0.05
0.3
-
0.05
-
-
-
-
500.
5
Physical
Color (b) - 15
Corrosivity - non-corrosive
Odor(b) - 3
Turbidity l(d)
Radionuclides(c)
Radium 226 plus 228 (c) 5
Gross Alpha Activity(c) 15
Gross Beta plus Photon Activity (e)
112
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TABLE 4-4. EPA WATER QUALITY STANDARDS FOR DISCHARGE TO GROUND
WATERS UTILIZED AS A DRINKING WATER SUPPLY (CONTINUED)
Maximum Allowable Level (a)
National Interim Proposed National
Primary Drinkinq Secondary Drinking
Constituent Water Standards Water Standards
Pesticides
Endirin 0.002
Lindance 0.004
Methoxychlor 0.1
Toxaphene 0,0005
Chlorophenoxys
2,4-D 0,1
2,4,5-TP Silver 0.01
(a) Expressed as milligrams per liter unless otherwise noted.
(b) Expressed as units.
(c) Expressed as pico-Curries per liter.
(d) May be 5 turbidity units or less for certain conditions.
(e) Shall not produce an annual dose equivalent to the total body
or any internal organ greater than 4 millirems per year.
(f) Limits of allowable range.
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The anions chloride and sulfate also have recommended
levels. Sulfate can cause distress in the lower digestive
tract of humans and animals. Chlorides impair the taste
of water when levels reach approximately 250 mg/1.
Dissolved solids and nitrates can place a definite impair-
ment on water quality for downstream domestic use.
Pesticides are detrimental to domestic use. Specific,
criteria are given in the references.
4.3.4 Fisheries
Water quality and stream hydrology limit the types of
fish which can live in a stream. Stretches of a river
which are periodically dried up cannot support signi-
ficant fish life. The water quality necessary to support
a suitable fish species diversity has the following pro-
posed limits: (McKee and Wolf, 1963):
1. Dissolved oxygen not less than 5 mg/1;
2. pH approximately 6.7 to 8.6 with an
extreme range of 6.3 to 9.0;
3. Specific conductance at 25°C, 150 to
500 mmho with a maximum of 1000 to
2000 mmho permissible for streams
in western alkaline areas (Note: total
dissolved solids (mg/1) generally equals
about 0.7 x specific conductance);
4. Free carbon dioxide not over 3 cc per liter;
5. Ammonia not over 1.5 mg/1;
6. Suspended solids such that the millionth
intensity level for light penetration will
not be less than 5 meters.
These should not be interpretted as maximum sublethal
levels. Rather, they are conditions favorable to a good
mixed warm water fish population.
Of the pollutants associated with irrigation returns,
sediment and temperature are probably most detrimental
to fish life. Sediment can cover the bottom of a stream,
burying fish eggs and covering the benthic invertebrates
which serve as food to many species of fish.
While many streams affected by irrigated returns have
significant aquatic life, many of these fish are carp
and other "trash fish." The proliferation of these fish
is mostly due to their tolerance to high temperature
water. This high temperature water is usually the result
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diversions drying up a river and fish having to survive
in the remaining pools. Habits of the carp generally
prohibit their coexistence with other fish species.
4.3.5 Recreation
Recreational water use includes swimming, boating, and
aesthetic enjoyment. Water quality requirements of
swimmable waters are:
o They must be aesthetically enjoyable,
i.e., free from obnoxious floating
or suspended substances, objectionable
color, and foul odors;
o They must contain no substances that are
toxic upon ingestion or irrigating to the skin
skin or human beings; and
o They must be reasonably free from pathogenic
organisms (McKee and Wolf, 1963).
Requirements for boating are mostly aesthetic.
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5.0 IRRIGATED AGRICULTURAL PRACTICES
AND POLLUTION CONTROL OPTIONS
The Environmental Protection Agency has defined best
management practices as follows:
"the term best management practices (BMP)
means a practice or combination of
practices that is determined by the state
(designated areawide planning agency) after
problem assessment, examination of
alternative practices, and appropriate
public participation to be the most effective,
practicable (including technological, economic,
and institutional considerations) means of
preventing or reducing the amount of
pollution generated by nonpoint sources
to a level compatible with water quality
roles."
The emphasis is clearly to reduce pollution at the source
rather than to treat pollution after it occurs.
For irrigated agriculture, improved irrigation practices
are the primary method of reducing pollution load at the
source. Alteration of conveyance systems, return flow
systems, and improved management of tillage practices
and chemical use may also be helpful.
Several practices are presented in this section. These
practices can be related to several broad categories:
Delivery Systems
Application Systems
Return Flow Systems
Chemical and Land Use Management
5.1 DELIVERY SYSTEMS
5.1.1 Conveyance Systems
Major losses of water occur through seepage from conveyance
facilities. On a national basis, delivery losses may be in
the range of 20 to 25 percent of the total diversion of
surface water ( Hagen 1967; Houk 1956).
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Seepage losses may or may not represent a pollutant
loading mechanism. In most areas, especially where soils
are alluvial, that portion of water lost from the delivery
system does not become degraded as it flows to the ground
water. In a few areas, however, geologic conditions
(saline soils or subsoils) may result in a significant
salt pickup by seepage waters. This has been shown to
be especially significant in the Grand Valley of Colorado
(Skogerboe & Walker, 1972). Seepage losses may be
detrimental when they result in non-beneficial consumptive
use and wet areas, as well.
Non-beneficial consumptive use of seepage waters occurs
along phreatophyte lined canals, in wet areas below canals,
and in areas where canal or ditch seepage otherwise
results in high water tables. While the amount of water
lost through these mechanisms (and the resultant concentration
of salts) may not be large, it is avoidable.
Delivery systems can be improved by lining open ditches
or conversion to pipelines. Slip form concrete lining and
PVC pipe has made upgrading smaller ditches feasible for
water conservation. Most irrigated areas have contractors
specializing in these operations, and price lists are
readily available.
Concrete slip form lining and pipelines are the most
popular permanent ditch upgrades. Other methods of reducing
seepage include: asphalt lining, flexible membrane lining,
chemical sealants, bentonite, compacted earth, and
corrugated metal.
It is difficult to evaluate the effect which canal lining
would have on pollution control. While reduction in seepage
can be predicted, the corresponding decrease in salt loading
is hard to evaluate (Skogerboe & Walker, 1972).
Seepage losses can be reduced to 0.03-0.06 m3/m2/day
(0.1-0.2 ft3/ft2/day) with a hard surface lining such as
concrete. Losses in unlined canals are highly dependent
upon soil conditions, but can be expected to be significant
in all but the more impermeable soils.
117
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Canal lining is limited by high costs of materials and labor.
In addition, many irrigation, canal, and ditch companies
own senior water rights to specified rates of flow.
Conveyance losses were considered in the granting of the
rights. With a sufficient right for irrigation and losses,
no incentive toward water savings is apparent. While
many on-farm ditches are lined, canals and laterals are
often incorporated among several users. These water users
would often rather spend money on their own farm than on
the incorporated canal.
5.1.2 Flow Measurement
In order to achieve efficient irrigation, farmers must know
how much water they are applying. Flow measurement of
diversion and tailwater is necessary to determine the
average amount of water applied to the field. Without water
measurement there cannot be water management.
Flow measurement is currently inadequate in most areas.
Where devices exist, they are often in poor condition and
may not be properly read. This condition exists because
excess water is guaranteed by right or the water is
inexpensive in comparison to labor and equipment costs.
Deep seepage losses have been found to be 50 percent of
applied water in the Grand Valley, Colorado and in the Snake
River Valley, Idaho ( Skogerboe 1975; Carter 1972).
Benefits to be derived from good flow measurement are
considerable. With flow measurement, the amount of water
applied can be easily calculated. Flow measurement is
necessary to apply the proper amount of water.« In addition,
good flow measurement insures fair distribution of water
among farmers preventing hard feelings during dry years.
5-2 IRRIGATION APPLICATION SYSTEMS - DESCRIPTION
There are three main methods of distributing water on the
farm: furrows, flooding, and sprinklers. Furrow irrigation
is used on approximately 54 percent of the irrigated-land,
flooding on around 30 percent and sprinklers on about
15 percent. Lesser used methods of irrigation include
subirrigation and trickle irrigation. Subirrigation is used
on less than 1 percent of the irrigated land. Trickle
irrigation is becoming popular on tree and bush crops,
although currently used on less than 1 percent of the
irrigated land. Each year, sprinkler and trickle irrigation
show an increased percentage of total irrigated acreage.
118
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Each irrigation method has limitations in terms of
crop, topography, soil permeability, and water supply.
In addition, each irrigation method has characteristic
return flow mechanisms. Figure 5-1 illustrates several
irrigation methods.
5.2.1 Furrow Irrigation
Furrow irrigation is the most widely used form of
irrigation. Furrow irrigation is popular because it
involves small capital investment, is well suited to
growing row crops, and may be used with most soils.
Furrow irrigation is equally suited to delivery
characteristics of wells or ditches.
Furrow irrigation may be used in soils having final water
infiltration rates from 0.25 to 7.62 centimeters/hour
(0.1 to 3.0 inches per hour). Extreme irregularity of
the water infiltration rate across a field makes furrow
irrigation difficult and inefficient. Topography is
significant in furrow irrigation and efficiency can suffer
greatly when slopes are irregular. Land forming is often
required in order to obtain correct slope.
Length of run is perhaps the most important factor in
determining potential efficiency with furrow irrigation.
The length of run and the number of furrows to be
irrigated by the available stream are the essential design
and operational factors, since the other factors
determining water distribution such as soil infiltration
capacity may be uncontrollable. Excessive length of run
is used on most fields to reduce labor requirements.
Excessive length of run can greatly reduce irrigation
efficiency.
The various types of furrow irrigation systems will be
described and discussed separately, since each has specific
characteristics which make general discussion insufficient.
Furrows
Furrow irrigation is characterized by slight slope, straight
alignment, large capacity, long reach, and use with row
crops ( Marr 1967). These systems are widely used and are
a familiar sight in most irrigated regions. Furrows are
essentially straight and may be from 0.1 to 0.8 kilometer
(1/16 to 1/2 mile) long, depending upon other conditions.
119
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division .
box 4.
BASIN OR LEVEL BORDER
FIG. 5-1. IRRIGATION METHODS CA3
CAD Redrawn from SCS Engineering Manual, Ch. 15, Irrigation
corporation
120
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LOW PRESSURE
PIPE LINE
CONCRETE LINED DITCH
check, drop S takeout
FIG.5-1.(cont.). IRRIGATION METHODS LA]
s
[A3 Redrawn from SCS Engineering Manual, Ch. 15, Irrigation.
_
toups
corporation
lovtlcnd, co.
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Topography is a limiting factor in the use of furrows.
A slight slope from the top to the bottom of the field
is required. This slope may vary from 0.05 to 2.0
percent under best conditions although slopes of up
to 4.0 percent are sometimes used ( Marr 1967).
Furrows are used for row crops including corn, cotton,
potatoes, sugar beets, beans, and vegetables.
Irrigating with furrow systems is essentially a full-
time job. The size of the stream of available water is
an important element in labor requirements. With small,
streams, only a few furrows can be irrigated at once.
Large streams allow more furrows to be in operation at one
time. Marr ( 1967 ) states that one man can manage around
0.057 m3/sec (2 cfs) for low intake soils and 0.198 to
0.227 m3/sec (7 to 8 cfs) for high intake soils.
Actual labor inputs are highly variable and appear to be
mainly affected by water availability and cost. Furrow
irrigation labor requirements may vary considerably with
field layout and water management practices. Estimates of
labor input for irrigation alone are:
Siphon tubes and dirt-head ditch 1.5-5.7
hours/hectare/irrigation
(0.6-2.3 hours/acre/irrigation)
Siphon tubes and concrete-head ditch 1.0-4.2
hours/hectare/irrigation
(0.4-1.7 hours/acre/irrigation)
Gated pipe 0.7-2.7 hours/hectare/irrigation
(0.3-1.1 hours/acre/irrigation)
Additional labor is required to pull in ditches, form
furrows, etc.
Lowest labor requirements occur when length of run is
excessive on an otherwise well planned field. These
lowest labor requirements are the result of only minimal
water conservation efforts. With a proper length of run,
labor requirements could be expected to be approximately
double the minimum expressed here. Improvements in the
distribution system, particularly gated pipe or concrete
head ditches, can greatly reduce labor requirements.
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Investment is "generally considered to be minimal with
furrow irrigation. Land forming will not be excessive
in suitable areas. The major capital cost would be
expected to be lateral construction. Annual maintenance
costs include furrow forming and ditch maintenance as
well as irrigation labor.
Corrugation Systems
Corrugations are similar to furrows except that they are
smaller in size. The smaller furrow streams associated
with corrugations allow them to be used on steeper lands
without erosion hazard. Either a small, continuous
stream or a larger, intermittent stream may be used for
corrugations.
Corrugations may be used or. steeper slopes due to the smaller
furrow stream. The general direction of irrigation remains
downhill. Optimum slopes are 2 to 4 percent for machine
harvested close-grown crops; 2 to 4 percent for pasture;
and 1 percent for row crops (Marr 1967). Allowable slopes
may be greater, up to 12 percent for close-grown crops
and pasture, on suitable soils.
Soils with a final infiltration rate of up to 2.54 centimeter/
hour (1-inch per hour) may be irrigated by corrugations.
Corrugations are especially suited for soils having low
final infiltration rates, down to 0.25 centimeter/hour
(0.1 inch per hour).
Corrugations are commonly used to irrigate close-grown crops
and pasture. Alfalfa and small grains are likely to be
irrigated by corrugations. Some small row crops may also
be irrigated by this method.
Contour Furrow Irrigation
As the name indicates, contour furrows run across-slope.
Contour furrows may be used for irrigation of orchards,
vineyards and bush crops on uneven terrain with slopes less
than 5 percent. Stability against erosion and breach by
the furrow water is a major concern. In areas of intense
rainfall, water may not drain off sufficiently resulting
in breaching and gully erosion.
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Perennial crops of trees and tree-like plants hold the
soil and may be grown on the steeper slopes with contour
furrows. This method is applicable to row crops only when
slopes are slight.
5.2.2 Border Strip Flooding
Border strip flooding is a controlled process. The area to
be irrigated is surrounded by a dyke. The land inside the
dyke is made as planar as possible with a slight slope from
the top to the bottom of the field. Alfalfa, pasture, and
other close-grown crops are commonly irrigated by this
method, although it is possible some row crops could be
irrigated by borders.
Border strips usually require considerable land grading.
Border strips may be 10 to 20 meters (30 to 60 feet) wide,
and 100 to 400 meters (330 to 1,320 feet) long. Down slopes
may be from 0.15 to 1.5 percent with 0.2 to 0.3 percent being
ideal. Cross slopes should be less than 0.2 percent.
Border strips are then restricted to fairly flat areas,
although with land grading there can be small differences
in elevations from one border to the next. In areas with
less permeable soils, the longer borders can be used.
Surface runoff is generally less than with furrow irrigation.
Because the entire surface is wetted, close growing crops are
used and the slope is carefully graded, streams large
enough to obtain good distribution may often be used without
an excessive erosion hazard.
5.2.3 Level Basin Flooding
In level basin flooding, the entire amount of water is applied
quickly and ponded until adsorbed. This method requires flat
bottom basins and a large intermittent water supply. It
can be effective with a wide variety of soil types. Basins
are leveled with laser controlled land leveling equipment.
Level basins have traditionally been used for rice, but
recent research has proven them effective for almost any crop.
Major requirements are level ground and a very large, available
water supply. Average required stream is about 0.007 m3/sec/
hectare (1 cfs/acre), although this varies with soil type.
No surface runoff occurs with this method, and excellent
distribution may be achieved. Level basin irrigation is
becoming increasingly popular, particularly in the southwest.
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5.2.4 Wild Flooding
Wild flooding involves the siphoning of water from contour
ditches. This method is generally used on steep or rolling
irregular land. It is commonly used in the irrigation of
pasture and close-grown crops. Wild flooding generally
results in poor water distribution and inefficient water use.
5.2.5 Sprinkler Irrigation
Sprinkler irrigation is adaptable to most major farm crops
with the exception of rice and orchards planted on steep
hillsides. This method provides a relatively high degree
of water control when coupled with proper management and
design. The sprinkler system should be designed to deliver
water at rates less than, or commensurate with, the final
infiltration rate. Surface runoff or tailwater is almost
completely eliminated using sprinklers and the amount of
water leaching through the root zone (leaching fraction) may
be reduced with attentive operation. Energy consumption
is the major disadvantage to sprinkler irrigation.
There are certain limitations in the use of sprinklers.
Wind may cause an unequal distribution of water, and in
hot dry climates improper application timing may result in
excessive evaporation. Water must be in constant supply and
free of debris. Salt deposits on leaves of certain crops"
may be detrimental if irrigation water is high in dissolved
solids, particularly chlorides. Sprinklers are not suited
to soils having infiltration rates less than 0.25 centimeters/
hour (0.1 inches/hour) (Pair 1966).
There are many types of sprinkler systems varying from fully
automated to labor-intensive hand-moved systems. Application
efficiencies are generally very high with sprinkler systems.
Well designed and operated systems approach 85 percent
distribution efficiency. Even application is a major benefit
of sprinkler systems. In addition, the amount of water
applied can be precisely controlled and monitored. A light
application can be made for seed germination, temperature
control, or for other reasons.
Evaporation losses from sprinkler systems are greater than
with surface systems. Evaporation losses are usually 2 to
8 percent of the total volume, but may be higher in extreme
circumstances. Evaporation losses at night are much less
and may be disregarded. Evaporation from wet foliage is not
an important loss (Frost 1963) . A method for determining
evaporation loss is presented by Frost (1963).
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There are several types of sprinkler systems including:
hand moved, side roll, portable solid set, and center
pivot. The center pivot has been the most popular by
far in recent years. Center pivots offer great labor
savings at a reasonable cost. Regular shaped fields are
required, and the corners are missed. Typical setup
involves the irrigation of 130 acres of a 160 acre quarter
section. Water supply should be constant, and problems
are sometimes encountered on tight soils. Design inputs
such as holding ponds, trash separators, wide tires or
built-up wheel tracks can make center pivots adaptable to
nearly any situation. The ideal situation is a quarter
section of fairly sandy soil served by a well. Energy
requirements are dependent upon total water use and total
pumping head.
5.2.6 Drip Irrigation
This system was developed in Israel over 15 years ago in
an effort to conserve water. Recently it has become quite
popular among the orchard growers in southern California.
It is adaptable to most soils. Costs have thus far
limited its use to high value crops. The system consists
of a pump, filter (the complexity of which depends on
supply water quality), pressure regulators (depending on
field gemoetry), and small diameter plastic pipe running
down tree rows with small emitters looping each tree.
The results produced by drip irrigation are a matter of
considerable discussion. On-going studies are showing that
the savings in irrigation water reported by some is largely
related to reduction in evaporation losses from the soil
surface prior to establishment of full-crop canopy and root
system. Certain specific problems, such as the possible
effect of toxic ions on plants have yet to be resolved.
Capital cost estimates vary greatly depending on terrain,
supply water quality, and spacing of trees. Recent
innovations in the industry coupled with an increased demand
have been lowering the cost.
Drip systems eliminate surface runoff, and considerably
reduce the quantity of leachate passing out of the root
zone. To date, application has been too limited to
consider drip systems a general solution to the agricultural
pollution problem.
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5.2.7 Sub-Surface Irrigation
Water is introduced through open ditches, tile drains
or moledrains. The crop is irrigated by artificial
manipulation of the groundwater surface elevation by
two methods: 1) the groundwater elevation is kept
at a depth below the root zone which will not saturate
the roots but will allow capillary action to supply
the plant with required moisture; 2) groundwater
elevation is periodically raised to fill the root zone
and then lowered. Use of this method is limited to
those areas which have good drainage, no salinity
problems, a sufficiently high groundwater elevation
or an impermeable layer to permit the formation of a
perched water table. Tailwater is not a problem with
this method of irrigation. Less than 1 percent of
irrigated agriculture is involved with this practice.
5.3 IRRIGATION APPLICATION SYSTEMS - COMPARISON OF
RETURN FLOW CHARACTERISTICS
Each method of irrigation has characteristics which make
it most suitable to a given set of conditions. In
addition, each method of irrigation has its own return
flow characteristics. Mitigating measures are often
required to utilize an irrigation method where conditions
are less than ideal. Such mitigating measures include
utilization of holding ponds to alter the time-flow
characteristics of the water supply, removal of trash and
sediment from water, and land leveling.
Each method of irrigation can be associated with specific
return flow characteristics. Management and water
measurement play an important role in the actual return
flow experienced. Certain alterations of the system
may significantly change return flow characteristics.
Presented in this section is a discussion of return flow
characteristics of the major irrigation methods.
5.3.1 Furrow Irrigation
Both furrow and border strip systems have water distribution
problems. These problems are the result of water being
applied at the top of the field and flowing down the field,
giving the top of the field considerably more opportunity
to take in water. Tailwater is essential if the lower, end
of the field is to receive sufficient water. The design
of surface systems limits them to a fairly narrow range of
application depths. Light applications for germination or
ground softening for harvesting are difficult with these
systems.
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TABLE 5-1. SUITABILITY OF IRRIGATION METHODS
to
oo
PRACTICE
Furrow
Border
Level Basin
Wild
Flooding
Sprinkler
WATER SUPPLY
Continuous or
Intermittent
Intermittent
Intermittent,
Large Stream
Continuous or
Intermittent
Continuous
SOIL
Medium
Preferable
Medium
Preferable
Fine or
Medium
Fine or Medium
Preferable
Medium or
TOPOGRAPHY
0.5 to 3.0%
0.5 to 3.0%
Dead Level
0.5 to 4.0%
0.0 to 5.0%
CROP
Row Crop
Generally used
on Close Growing
Crop
Any Crop
Close Growing
Crop
Any Crop
Drip
Sub-
Irrigation
Continuous or
Intermittent
Intermittent
Coarse
Preferable
Fine, Medium
or Coarse
Impermeable
Layer or
Water Table
at 4 to 12 ft.
Any
Topography
0.0
Tree or Bush
Crops
Any Crop
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TABLE 5-2. TYPICAL RETURN FLOW CHARACTERISTICS OF IRRIGATION METHODS
IRRIGATION METHOD
DEEP SEEPAGE
TAILWATER
to
Furrow Irrigation
Excessive Length
of Run
Proper Length of
Run
Cut Back Operation
Proper Length of
Run
Border Irrigation
Level Basin
Wild Flooding
Sprinkler
Drip
Sub-Irrigation
25-60%. Excessive length of
run results in poor distribution
and excessive leaching of top of
field.
10-35%. Fairly even distribution
can be achieved. Measurement and
management are key to good
efficiency.
10-30%. Very good distribution
can be achieved.
10-60%. Highly variable
depending upon design, soils,
measurement and management.
Efficient when properly used.
5-30%. Good distribution;
highly efficient. Good
measurement and management
facilitated.'
15-50%. Highly variable depending
upon operations.
5-30%. Good distribution; good
management can result in high
efficiency.
5-25%.
10-70%. Highly variable
3-10%. Excessive
length of run reduces
tailwater. Bottom of
field may be under
irrigated.
5-20%. Runoff is
required to get water to
the end of field.
3-10%. Cut back operation
can greatly reduce
tailwater.
0-10%.
0.
0-10%,
0.
0.
0.
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Opportunity time is the time between the advance of
the wetting front and the recession of standing water
after shut off. The amount of water entering the soil
is a function of the opportunity time. Figure 5-2 shows
advance and recession curves. Figure 5-2a shows the
typical case where the head of the field takes in more
water than the lower end. Figure 5-2b shows the ideal
case where a nearly equal opportunity time is available.
Figure 5-2c shows the advance and recession curves for
the case of excessive length of run. Figure 5-3 shows
how water is likely to be distributed in the soil.
Distribution can be optimized by using an appropriate
length of run. Cutting back on the flow may also aid
in optimizing distribution.
The amount of water lost to deep seepage and tailwater
is highly variable. Deep seepage losses are a function
of soil type, length of run, slope, stream size, and
management. With tight or medium soils, regular slopes,
proper length of run and good management, deep seepage
losses from furrow irrigation need not be excessive.
Furrow irrigation can be highly efficient with proper
design and management. Excessive length of run is a
common problem in furrow irrigation. Excessive length
of run is common and is the result of a desire to minimize
labor requirements at the expense of cheap water. Sandy
soils with high infiltration rates are especially
susceptable to poor water distribution when length of
run is excessive. Excessive nitrate and salt leaching
may result. In addition, the over application of water
to the top of the field often results in drainage problems,
The amount and quality of tailwater resulting from furrow
irrigation is also quite variable. Tailwater volumes
resulting from proper length of run and good distribution
may be 15 to 20% of the applied water. In practice,
tailwater volumes are much less. This is because the
length of run is nearly always excessive. Typical
tailwater volumes are 5-15% of the applied water. The
amount of sediment, phosphorous, and pesticide carried
in the tailwater is a function of soil type and furrow
stream velocity as well as total tailwater volume.
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DISTANCE DOWN FIELD
FIG. 5-2. TYPICAL CURVE
DISTANCE DOWN FIELD
FIG. 5-2. IDEAL CURVE
DISTANCE DOWN FIELD
FIG.5-2.C EXCESSIVE LENGTH OF RUN
FIG. 5-2. ADVANCE RECESSION CURVES FOR SURFACE
IRRIGATION
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(a) IRRIGATION DEPTH WITHOUT MANAGEMENT
® IRRIGATION DEPTH WITH MANAGEMENT
© OVER IRRIGATION DUE TO IMPROPER APPLICATION
(d) OVER IRRIGATION NECESSARY ON SURFACE IRRIGATION
(e) WATER THAT COULD BE REUSED WITH TWR SYSTEM
FIG. 5-3. SURFACE IRRIGATION SOIL PROFILE
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Potential for Increased Efficiency
Measures which may reduce return flows include using the
proper stream size, cut back irrigation, land leveling,
altering the length of run and proper irrigation timing.
Proper Stream Size. Alteration of stream size
represents tne oasic level of system improvement.
Because conditions of soil moisture and vegetation vary
through the season, a fixed stream size will not provide
optimum conditions. The stream size must be varied for
changed conditions in soil surface, compaction due to
tractor, weather, soil moisture, and crop cover. Stream
size is varied by controlling head on input or changing
siphon size when water is applied by the ditch siphon
method. This represents a labor-intensive situation which
is difficult to achieve.
Distribution to furrows by gated pipe offers greater
operational controls. Stream size can be optimized such
that intake opportunity is more nearly equalized down
the field. This can be done by analyzing advance
recession curves. Obtaining a proper flow to furrow or
border is currently sought by farmers, but further
improvement will be likely to come only with labor saving
devices which offer better water control combined with on-
farm technical assistance.
Cut Back Irrigation. Reducing stream size at the
proper time can provide a significant increase in
irrigation efficiency by reducing tailwater. Distribution
efficiencies may also show increases with cutback operation
(Sakkas and Hart 1968). Cut back operation has often been
abandoned by farmers due to the increased labor demands
incurred.
Cutback operation can result in significant reductions in
tailwater. In practice, the furrow stream is reduced as
it approaches the end of the field. A smaller stream is
used for the remainder of irrigation. Since runoff occurs
during the flow of the smaller stream, erosion will be less
and, the runoff is likely to contain a lower concentration
of sediment. This is true because the erosive tendency of
the smaller stream is much less.
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Cutback operation is difficult to achieve when water
is distributed to furrows by a ditch with siphon tubes.
Operational limits exist on the range of head which
can be put on the tubes. It is not considered practical
by farmers to change tubes to a smaller size during an
irrigation. With ditch and siphon tubes, the only
practical way of cutting back is to start with two
tubes and switch to one after the water reaches the end
of the field.
With gated pipe, operational controls allow easy cutback
operation either by changing gate openings or by adjusting
a valve before the gated pipe.
A problem exists with cutback operation because most farms
are delivered a constant flow of water. This problem may
be dealt with by two methods: equilization ponds or
dividing water between two sets. Equalization ponds can
absorb fluctuating outflows with constant inflows. As
an alternative, one set can be given a full stream, turned
off, and a final set made which irrigates both sets by
dividing the water between the two. Water may also be
distributed by having a small stream set follow a large
stream set as irrigation proceeds across the field.
An automatic cutback system operated by varying head on
spiles has been demonstrated. Such a method could provide
cutback operation without increase in labor. ( Nicholaescu
and Kruse 1971).
Cutback operation can greatly reduce the total valume of
tailwater. In addition, an improvement in distribution
efficiency can be realized. A reduction in concentration
of sediment and associated pollutants in the tailwater is
also expected. Cutback operation will be widespread only
when labor saving devices are combined with on-farm
technical assistance.
Slope Modification. Land leveling has been
popular with farmers striving to obtain more workable
fields. It is necessary to do some land leveling for
border irrigation, and there is a significant proportion
of furrow irrigated fields which have been leveled. Land
leveling is done to remove high and low spots and to obtain
a proper slope for irrigation.
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Length of Run Alteration. Overly-long irrigation
runs can make it difficult to apply sufficient
water to the end of the field ana causes excessive water
application to the top of the field. Shortening
irrigation runs can result in increased application
efficiency with smaller furrow streams. Farmers are
hesitant to divide one long field into two short ones
because increased labor is required for irrigation and
machinery operation is made much more difficult.
Timing of Irrigation. Improvement in irrigation
timing may be effective in reducing return
flow volumes. Such improvements in timing may require
an educational effort. Irrigation scheduling services
offer this educational effort. _,
5.3.2 Border Irrigation
Border irrigation has many of the same characteristics
as furrow irrigation. Water is introduced at the top
of the field to flow overland towards the bottom. The
combined influences of soil, flow rate, slope, and length
of run work in the same manner.
Border irrigation is used with close growing crops. Land
leveling is used to create a planar surface, and slopes
are nearly always less than 2 percent.
Excessive leaching losses may occur in border irrigation
as well as in furrow irrigation. These leaching losses
are highly variable depending upon the above mentioned
factors.
Tailwater resulting from border irrigation is generally
from 0 to 10% of the applied water. Theoretical tailwater
volumes may be larger, but excessive length of run is the
general case in practice.
The fact that border irrigation is used for close growing
crops means that sediment concentrations in the runoff
are less than with furrow irrigation. Also contributing
to this lesser erosion is the hydraulic nature or border
irrigation, i.e., a slow moving sheet of water.
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With proper management, border irrigation can be
highly efficient. High efficiencies can exist when
design (width and length of border) is proper for the
soil, slope, and available stream of water. Combined
with good operations, high efficiencies can be
expected and return flows minimized.
Potential for Increased Efficiency
Several potential improvements to border irrigation
exist. The two major improvements include utilization
of a concave slope (decreasing slope towards the end
of the field) and cut-back irrigation. Both of these
changes would serve to make water flow faster over the
top of the field and slower over the end of the field.
Cut-back irrigation for borders can be conducted in
much the same manner as with furrows and will not be
discussed separately here.
Concave slopes have been analyzed by researchers who
have found that they increased uniformity without
complicated cub-back operations which are likely to be
abandoned due to the considerable labor involved. Concave
slope results, as presented in fable 5-3, indicate better
efficiency.
5.3.3 Level Basin Irrigation
Level basin irrigation can be used to achieve extremely
high efficiency. Surface runoff is eliminated. Uniform
application and the visual impact of ponded water
discourage the application of excess water.
5.3.4 Wild Flooding
Wild flooding or contour ditch flooding is generally
used for the irrigation of marginal pastureland, or on
rolling land used to produce hay* It is used primarily
where other methods of irrigation are limited by topography
or other economic factors such as short water supply,
short growing season, etc.
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TABLE 5-3. CONCAVE SLOPE RESULTS ON BORDERS
Powell, Jensen, & King 1972
Ten Segment Concave
Four Segment Concave
Uniform Slope
Four Segment Convex
CU
96.6
95.7
89.9
79.8
Runoff
%
15-1
15.3
17.5
15.3
Advance
Time
(min)
345
339
309
336
CU = coefficient of uniformity = 1 - y
d
where
y = average of absolute values of the deviations in
depth of water stored from the average depth of
water stored
and
d = average depth of water stored
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5.3.5 Sprinkler Irrigation
Sprinklers are a very efficient method of irrigation.
Surface runoff does not occur with most systems.
Distribution efficiencies are often about 85% ( Sakkae
& Hart 1968). In addition, leaching has been shown
to be most efficient under unsaturated conditions.
Management of soil moisture and irrigation timing are
the only real limitations to reduction of return flow.
5.3.6 Drip Irrigation
Drip irrigation results in only minimal return flows.
Surface runoff does not result from irrigation. Some
leaching is necessary, but control is generally good.
5.4 IRRIGATION MANAGEMENT AND EFFICIENCY
Efficient irrigation is the key to reducing return flows.
Good irrigation management requires a well designed
application system and proper use of that system. Proper
water use requires knowledge of crop evapotranspiration,
soil-moisture capacity, the amount of water to be applied,
and the timing of that application. Good flow measurement
is essential for good water management—this is discussed
in Section 6.1.
5.4.1 Irrigation Management
Irrigation management is as much an educational process
as upgrading of irrigation systems. Items involved in
achieving better irrigation efficiencies through better
management are:
Measurement of water deliveries and runoff
Having a properly designed system
Using the proper stream size and time of irrigation
set to achieve good distribution
Making the necessary commitment to operations
Knowledge of crop use and soil-moisture capacity
to determine amount and timing of next irrigation.
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While increased efficiency can be expected from more
intensive management of existing systems, an input of
additional labor is required. This additional labor
input is almost impossible to achieve under current
conditions. Labor-saving devices offer some promise in
reducing direct irrigation labor, thereby reducing the
time, labor, and money gap between recognition of what
should be done and what is actually done.
Irrigation efficiencies currently suffer because
inexpensive water can be substituted for the more
expensive input of additional labor. This is often due
to an over allocation of water. Figure 5-4 shows the
relationship between water cost and irrigation efficiency
on eleven USSR study sites ( USDI-USBR 1973).
5.4.2 Scientific Irrigation Scheduling
Scientific irrigation management services (ISS), also
referred to as irrigation management, involves the
utilization of a consultant by the farmer in order to
schedule irrigations and plan irrigation practice. The
service generally involves personal visits to the farm
by a trained technician. In the case of sprinkler irrigation,
flow measurement of diversions is a must. The basis of
the system is the accounting of evapotranspiration
requirements and root zone moisture so that irrigations
may be predicted. This accounting is generally done using
climatic data and computer simulation of inputs and with-
drawals from the soil moisture.
Irrigation scheduling services vary as to the amount of
service offered. The Bureau of Reclamation has offered
three levels of service. The Irrigation Guide is a weekly
bulletin sent to the farmer. It gives information on
consumptive use, amounts of water to apply and irrigation
intervals. No visits are made to the farm. The farm
method incorporates visits by a technician, and irrigation
data is more detailed. A soil storage coefficient based
upon a farm visit is incorporated in the program and based
upon the last irrigation date and the expected time of
the next irrigation is predicted. The field by field
method utilizes soil, crop, and day of last irrigation
data for each field together with evaportanspiration data
and visits by a technician. This method predicts the
optimum day for irrigation in each field. For our
discussion, we will describe the components of an intensive
irrigation scheduling service.
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ao
I
eo
s
40
1
I
zo
-ST
' ~-
5-—""""^
•
•
•tfMVH^M«M^B^^«^««^ta^*
^
^^^^^^^^^^^^^M^^BMM-MI
^
\ 1
^
1965 - 1970
DATA FROM ELEVEN WATER USE
STUDY SITES
(DOES NOT INCLUDE DATA WHERE
CROPS WERE SERIOUSLY STRESSED
1
/
)
0 1 2 3 4 S e 7 8 9 10 II IZ
AVERAGE COST (DOLLAR PER ACRE -FOOT)
FIG. 5-4. DATA SHOWING RELATIONSHIP BETWEEN IRRIGATION
EFFICIENCY AND WATER COST CA]
CA3USDI, 1973
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The first component of ISS involves visits by
technicians trained in soil and water relationships.
Such visits are likely to occur on a weekly basis.
While on the farm the technician should check
soil moisture at several places and depths. This
may be done using traditional methods such as feel,
augers, porus cups, and tensiometers. Samples should
also be taken for gravemetric oven analysis. The
soil should be analyzed for water holding capacity,
wilting point and field capacity for gravemetric and
suction analysis in the lab. New devices such as neutron
probes will be calibrated to laboratory soil moisture
analysis as they become'refined and costs are reduced.
When new soil water measuring devices become more
developed, it is expected that they will replace many
of the traditional devices.
The technician should also test infiltration rates
at several places in the field. Infiltration rates
vary through the season and this should be studied
as well. The technician should give advice on
irrigation practice to the farmer. This advice would
be based upon observation of advance and recession
characteristics in surface irrigation as well as the
soil moisture status, holding capacity and infiltration
rate. The technician should advise the farmer of the
necessary depth of application and the size of the
furrow stream and time of set necessary to achieve this
application. The technician should also be prepared to
aid the farmer in considering and seeking engineering
help for system improvements.
Perhaps the most important job of the technician is
to communicate. All of the data collected on the farm
and from the computer simulation is no good unless it
can be communicated to the farmer who is the final judge
of when and how to irrigate. The farmer must gain
confidence in the service in order to continue as a
subscriber.
Initially, technician visits to the farm must be fairly
frequent, perhaps greater than once per week. As time
progresses, visits can be fewer, although weekly visits
are advisable.
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Flow measurement is the next element involved in
irrigation management. Without flow measurement
there can be no irrigation management. With
sprinkler irrigation, it is desirable to measure
diversions in order to determine the net water
application rate.
A number of methods are presently available for
determining the timing of irrigation applications.
The aspect of irrigation timing represents an extremely
vital service provided by an irrigation scheduling
program. The sophistication of the effort expended in
defining water scheduling varies from:
Mere publishing of pan-evapotranspiration data;
Calculating evapotranspiration for various crops
in a general area using wind-run, pan-evaporation,
temperature, and solar radiation;
Field by field calculation of evapotranspiration
which considers not only climatological data and
type of crop, but also planting date;
Intensive periodic measurement of field soil
moisture as a means of determining crop
evapotranspiration.
When evapotranspiration is calculated, computers are
used in all but the most primative of services. The
efficiency of the computer in processing data allows
evapotranspiration to be computed through use of
relatively sophisticated analytical procedures, such as
that represented by the Penman method.
When an irrigation scheduling program includes on-farm
field service, accuracy of water application timing is
often improved. Field service involves:
Assessment of available soil moisture through
neutron probe testing, speedy moisture meter
testing, or soil sampling and oven testing;
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Prediction of future crop use based on
computed evapotranspiration or based on
the periodic change in soil moisture;
Prediction of next irrigation by
establishing the date when available
soil moisture will be on the order of
50 percent.
A graphical analytical procedure based on neutron
probe soil moisture determination has been proven
to be an effective means of guiding irrigation
scheduling activities. To schedule an irrigation
correctly, two criteria are needed:
Determining the amount of water available
to a crop;
Determining the water use rate by the
particular crop.
Timing of a required irrigation is established by
means of relating available water to the water use
rate. Assessing available water has been simplified
to a great extent through use of the neutron probe.
To correctly schedule an irrigation by using the
neutron probe requires identification of the refill
point (the point at which irrigation should occur)
and periodic moisture measurements by the neutron
probe. No other information is needed. Periodic
measurement of soil moisture will describe both the
ambient soil moisture and the rate of water use by a
particular crop (Gear, et al., 1977).
A simple graphical analysis can then be used to
accurately forecast the date of the next irrigation.
This is done by plotting soil water content versus
time on a graph, with the refill point indicated.
Potential errors created by interim weather change
are quickly and accurately accounted for by plotting
a subsequent neutron probe measurement (ibid).
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ISS is catching on and is expected to grow
considerably. Jensen (1975) conducted a survey
of firms offering such services in 1974. He
surveyed only services which offered at least one
visit per week to the farm and which used computer
simulation. In 1974, field by field ISS was
provided to 7,900 fields and approximately 3 million ha
(7,385,000 acres) by all groups.
In 1974, at least ten commercial firms offered
services in eight states on approximately 3 million ha
(7,250,000 acres) of land. Of the commercial firms,
most offered nutrient advice and about half offered
pesticide and irrigation system improvement advice
as well as scheduling. Nearly all of these services
based scheduling on climatic data and deemphasized
in-field soil moisture measurements as input to the
computer program. Soil moisture was monitored mostly
by probe and feel methods, practices which were
subsequently used as a backup to the computer data.
The reliance on these methods emphasizes the importance
of development of neutron probes and other quick moisture
measuring techniques.
In addition to the commercial ISS, two state agencies
and the Bureau of Reclamation offered services. These
agencies accounted for 54,000 ha (133,000 acres).
Operation of the free agencies was similar to the
commercial firms, although less services were offered.
Irrigation scheduling by itself is not a panacea for
controlling pollution from return flows. Combined with
improved on-farm practices it may be quite effective,
however. Loading of nitrates is also reduced considerably
since the amount of leachate is reduced. While actual
improvements in on-farm practices cannot be expected to
equal demonstration projects, significant reductions
could still be achieved. With enough incentive, on-
farm practice could be greatly improved, but unfortunately
little incentive exists.
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Minimum leaching is a concept of leaching only
enough water from the root zone such that crop
yields are not reduced. At least some crops are
insensitive to the leaching fraction as long as a
minimum leaching fraction is achieved ( Van
Schilfgaarde 1974).
While adoption of minimum leaching fractions could
greatly reduce salt loading in drainage, it is a
long way off. Irrigation systems don't distribute
water evenly enough, and farmers are unlikely to
cooperate.
The concept of minimum leaching is valid and has been
proven (Van Schilfgaarde 1974; King, Hanks 1973).
Using soil salinity sensors as an additional input to
irrigation scheduling programs combined with sprinkler
or trickle irrigation is a workable method of reducing
salinity loading. While computer scheduling is here
today, adopting minimum leaching is in the distant future.
The impact of crop yields has been demonstrated by the
Bureau of Reclamation. For areas where irrigation
scheduling was used, crop yields were increased by
around 15 percent.
Since drainage water eventually finds its way back to
the stream, flows downstream would not be changed.
Farm efficiency can be expected to increase 10 percent
(Jensen 1975) , however. This water would be available
to other non-consumptive users through the section.
Increased quality through less leaching means downstream
users would not have as much salt to leach. Efficiency
improvements represent a benefit although they may not
be quantifiable in terms of total water consumptively
used in a basin.
The success of existing scheduling services indicate
that few severe problems exist. Further development is
needed on crop-use curves, and rapid soil moisture
measuring techniques. In addition, there is a shortage
of trained or experienced employees as with anything new
(Jensen 1975). In many cases, irrigation systems need
improvement and flow measuring devices in order to
realize the benefits of ISS.
145
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There are no direct institutional conflicts toward
the implementation of ISS. The resistance to change
represents a problem, but is being overcome by the
evidence of the benefits of ISS.
Many areas of the country could benefit from such
services where none exist. The development of
services in these areas may be slow in coming
without government incentive. Many services offered
to farmers now are supported by taxes. Irrigation
scheduling has proven successful as a commercial
enterprise and has many benefits as such.
5.5 EXCESS WATER REMOVAL SYSTEMS
Systems which carry away tailwater and excess leachate
represent the connection between the return flow
from a particular field and an actual water quality
impact. Alternatives in water removal systems can
have effects upon water quality.
5.5.1 Tailwater Systems
Tailwater returns are generally carried away by a ditch.
These returns are often directly re-used for irrigation
of lower fields or farms, and in this case do not impact
water quality. Where tailwater return flows impact
water quality, alterations to the return flow system
may be able to reduce pollution. Tailwater return
systems, mini-basins, sedimentation ponds, grassed
wasteways, and buffer strips are examples of such
alterations to the return flow system.
Tailwater Recovery
Tailwater recovery involves catching tailwater from surface
irrigation and pumping it back for use on the same farm,
or using tailwater on a down slope field. With tailwater
recovery, surface runoff and associated pollutants
(phosphorous, sediment, and the majority of pesticides)
can be reduced to zero. Tailwater return systems may
either return water as it arrives at the bottom of the
field or use a storage facility to hold water for later
use. Tailwater systems have paid for themselves in
several areas.
146
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Phosphorous and sediment are recognized as being
transported by surface runoff (tailwater). In
addition, surface runoff is a major transport
mechanism for pesticides. Tailwater reuse is not
considered to be effective in reducing loadings of
nitrogen or salts.
Reduction in pesticide loading would be related to
the transport mode of the particular pesticide.
Sedimentation Basins
Sedimentation basins may be used to settle out some of
the sediment. Such basins may be constructed by
damming up natural stream beds, gullies or draws,
or by excavation. The sediment trapped can be utilized
in turning gullies into usable land or redistributed.
Sediment ponds must be considered a short term
solution, since they become filled up (Robbins and
Carter 1975).
Sediment ponds are only effective in trapping sands
and silts. While some clay will settle in a pond with
sufficiently low flow-through velocities, the proportion
of the total clay removed is small for most pond designs.
Most sediment attached phosphorous and pesticides are
attached to the clay particles. Thus, while some removal
of phosphorous and pesticides may be expected, the
proportion will be smaller than the percent of sediment
removed by weight. However, phosphorous output in an
Idaho study was significantly reduced (Bondurant et
al 1975) .
Removal of clay particles requires techniques other
than sediment ponds such as chemical flocculation or
vegetated strips (Carter 1976). If ponds receive a high
loading and are to be of continued service, they must
be cleaned on a seasonal basis. A dragline or other
equipment may be required for the cleaning ( ibid).
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The ideal pond is triangular in shape with a narrow
entry and a wide exit to allow a continually
decreasing forward flow velocity. Forward velocity,
particle size and length considerations are displayed
on Figure 5-5. These considerations are based on
Stokes law and are not applicable to clay particles
(Bondurant, et al 1975). Pond design should consider
volumes of sediment expected and the size breakdown
of this sediment. The usefulness of the pond is
governed by its ability to remove the particles
causing the pollution problem.
In the Twin Falls, Idaho area, considerable work
has been done with sedimentation basins. Sediment
has been a significant water quality impairment to
the Snake River and ponds have been used effectively
in reducing the load. These ponds are considered to
be a short-term solution ( Robbins and Carter 1975.)
The more sediment-laden the water, the more effective
the pond. Sedimentation basins are not effective in
removing disaggregated clay particles. While design
and construction may be fairly simple, ponds must
either be cleaned out if sediment loads are significant
or allowed to fill in. Ponds which are allowed to fill
in eventually lose their effectiveness and other control
measures must be taken. Cleanout represents a
continuous maintenance requirement and requires heavy
equipment which the farmer may not have.
Mini-Basins
0
Mini-basins are small shallow ponds constructed on
the lower end of a field by putting in a low berm
along the bank of the drain ditch. Other berms are
constructed perpendicular to the drain ditch, so that
each basin retains the tailwater flow of just a few
furrows. The berm along the drain ditch also serves as
a spillway when necessary, so it should be seeded with
grass to minimize erosion into the ditch. Mini-basins
typically retain 90 to 95% of the sediment. ( Fitzsimmons
et al, 1977; Lindeborg et al, 1977).
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!
£*.
U3
SETTLING VELOCITY (FT./SEC.)
FIG. 5-5 POND LENGTH REQUIRED FOR QUARTZ PARTICLES TO SETTLE ONE FOOT AT
VARIOUS FORWARD VELOCITIES, USING STOKES* LAW LA:
LA] Bondurant, 1975.
toups
corporation
lowland, co.
-------
Buffer Strips
Strips of close growing crops at the end of the
field—including grass, grain, or hay—have been
found effective in reducing the sediment load
resulting from tailwater runoff. The slow move-
ment through these crops results in the settling
of a portion of the suspended solids. Results
varied from about 40 percent removal to over
90 percent removal, depending upon conditions.
(Fitzsimmons et al, 1977).
Grassed Waterways
Vegetated return flow channels can be highly
effective in settling out sediment. Depending
upon the type of vegetation, the vegetated channel
may potentially serve a dual purpose as pasture,
hay ground or wildlife habitat.
5.5.2 Drainage
While variations of subsurface drainage systems
have been studied for pollution control, they are
not widely adaptable and won't be extensively
reviewed here. Articles dealing with using
submerged drains for denitrification or using
shallow drains to remove only the shallow, less
saline groundwater are listed in the Bibliography.
5.6 SOIL CONSERVATION PRACTICES
Traditional soil conservation measures may be effectively
used as a pollution control option. Yet many traditional
techniques successful under rainfall conditions do not
apply to furrow irrigation ( Mech and Smith 1967) . Such
measures are aimed at reducing runoff and erosion. In
arid irrigated regions, rainfall of sufficient magnitude
to cause erosion is infrequent (Carter 1976). Furthermore,
irrigation by good sprinkler systems will produce no
runoff, and border systems are generally confined to flat
ground with close growing crops offering minimal erosion
potential. Furrow irrigation on the other hand has
significant erosion potential and is the predominate
form of irrigation.
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Soil conservation measures may conflict with irrigation
practice and pollution control in two ways: 1)
irrigated agriculture may require high value crops
year after year in order to be economically favorable;
2) minimum tillage measures may not be favorable from
a production standpoint and while reducing sediment
loading, may increase loadings of nitrogen and
phosphorous when chemical fertilizers are added to the
surface ( Romkens 1973). While conflicts may rule out
some types of soil conservation measures, others may
prove to be effective.
Erosion control methods may either reduce runoff or
reduce erosion. Most methods are effective at both.
Carter (1976) lists ten general methods including:
1) Eliminate or reduce irrigation return flows
when conditions permit by using irrigation
methods with little or no runoff (such as
sprinkler or truckle irrigation, discussed
elsewhere in this report);
2) Put furrows on the contour and decreasing
slope towards the end of the furrow;
3) Control furrow stream size and make proper
stream adjustments adequate measurement,
and controls as necessary;
4) Shorten length of run;
5) Control the irrigation duration to reduce
the number of irrigations per year.
Alternate furrow irrigation may also reduce
contact;
6) Cultivate only when necessary avoiding
excessive soil loosening which increases
erosion and soil loss;
7) Control tailwater by assuring that it flows
slowly enough that sediment settles before
the water leaves the field. Filtering
through grass strips removes sediments;
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8) Utilize sedimentation basins to remove
sediment from return flows.
Most of these options are discussed elsewhere in
this report. Others are self evident. Quantitive
prediction of results is only possible for no runoff
options. Other options cannot be quantified as to
effectiveness without individual site analysis.
Cultivating only when necessary is a traditional soil
conservation method. Soil losses may be around 10
times greater after the first irrigation after cultivation
than during succeeding irrigations (Mech and Smith 1967).
While soil losses may be less under minimum cultivation,
losses of surface applied fertilizer may be higher
(Romkens 1973). Problems might be encountered in using
conservation tillage, since salt accumulations at the
furrow peak may have to be plowed under.
Rainfall area soil conservation practice includes no
till planting in prior crop resideues, conservation
tillage, sod based rotations, meadowless rotations,
winter cover crops, improved soil fertility, timing of
field operations, plow-plant systems, contouring,
graded rows, contour strip cropping, terraces, grassed
outlets, ridge planting, contour listing, change of
land use and others (Stewart et al, 1975). While it is
good to know these methods since they may prove useful,
they are not generally applicable to irrigated agriculture,
5.7 FERTILIZER RESOURCE MANAGEMENT
Management of fertilizer applications has significant
potential for reducing nutrient pollution. Fertilizer
management involves using optimum application rates,
timing and type of fertilizer, as well as proper
incorporation into soil. Water management must also
be considered as a fertilizer management tool, as must
erosion control. Best management in fertilizer use
creates benefits for both the farmer and the environment.
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The application of more fertilizer than can be
effectively used by the crop is a situation of
waste. Determining nitrogen fertilizer requirements
is difficult. No rapid soil test is available to
provide an adequate estimate of soil nitrogen available
to crop during a season. Field tests combined with
local experience appears to be the best tool currently
available. Timing fertilizer applications and water
applications is perhaps the most important aspect.
If spring leaching for salts is practiced, nitrogen
should be applied afterwards.
Rotating crops from high nitrogen users (such as
corn) to plants not requiring chemical fertilizer,
especially deep rooted ones such as alfalfa, can
be effective in the utilization of nitrates in the
lower portions of the soil (Stewart 1975).
Unfortunately, economics may dictate a mono-culture.
Minimizing leaching while maintaining a safe
salinity level in the soil is the most significant
way to control fertilization, especially if
coordinated with proper fertilizer application rates
and well planned timing of fertilizer use.
5.8 EFFECTIVENESS AND COST OF POLLUTION CONTROL
The cost of altering practices for pollution control
should not be considered in terms of cost of the
practice along, but also should take into consideration
the change in labor requirements, crop yield, and other
operation and maintenance costs which result. Costs
vary not only with time, but also with locale.
Effectiveness for pollution control options is also
very highly dependent upon the specific application
involved. Soils, crops, and other localized conditions
make a difference.
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Increased irrigation efficiency (reduced leachate
and runoff) is the only universally effective method
of irrigated agriculture pollution control. Other
methods of pollution control tend to deal with
specific pollutants.
In this section, pollutant control options will be
discussed as they relate to specific pollutants.
This information is summarized in Table 5-4. The
effectiveness of control measures presented here
relates only to the results which can be achieved
in a particular field or application site.
Effectiveness on the basin-wide level is complicated
by re-use of return flows, changes occuring during
transport, etc.
5.8.1 Salinity
The effectiveness of salinity control options is
dependent upon local conditions. In most areas,
salinity levels are due to consumptive use alone.
In a few areas, however, weathering of saline rocks
and soils has been shown to represent a significant
salt load. In these areas, potentials for reducing
salt load are much greater.
Where consumptive use is the only significant cause
of increased salinity, the potential for reduced
salinity loading is very small. Strategies aimed at
reducing salinity concentrations must either reduce
non-cropland consumptive use, reduce cropland
consumptive use, or increase salt storage in and
below the root zone. These strategies, with the
exception of salt storage below the root zone, are
aimed more at reducing concentration by making more
water available. Such strategies may then be evaluated
in terms of water conservation potential.
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TABLE 5-4 ESTIMATED REDUCTION IN POLLUTANT LOADING FOR VARIOUS
CONTROL OPTIONS AS COMPARED TO FURROW IRRIGATION
Pollutants
Control Option
Irrigation
Scheduling
Lateral Lining
& Pipeline
Canal Lining
Improve Surface
Systems (2)
Sprinklers
Dead Level
Irrigation
Land Leveling
Drainage
Water Measure
Device
Mini-Basins
Sediment Ponds
T.W. Pumpback
Buffer/Filter Strip
Grassed Waterways
Slow Release
Nitrogen
Reduction In
Deep Seepage
Water Loss
5-10%
5-20%
5-20%
5-30%
20-50%
20-50%
0-25%
5-20%
0- 5%
0
0
0
0
0
0
Nitrates
5-10%
0
0
5-30%
30-50%
20-50%
0-25%
0-10%
0- 5%
0
0
0
0
0
10-30%
Sediment
0- 5%
0-10%
0-10%
10-60%
90-100%
100%
0-10%
0
0- 5%
85-95%
40-90%
50-100%
30-60%
5-40%
0
Phosphorous
0- 5%
0
0
10-60%
90-100%
100%
0-10%
0
0- 5%
85-95%
40-90%
50-100%
30-60%
5-40%
0
Pesticides
(1)
0- 5%
0
0
10-60%
90-100%
100%
0-10%
0
0- 5%
85-95%
40-90%
50-100%
30-60%
5-40%
0
(1) Pesticides traveling with soil only.
(2) Improve distribution system, proper length of run, cut back operation.
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In this context, water conservation potential means
reduction in consumptive use only. As an example,
assume a canal to an irrigation project lost 25
percent of its water to seepage and phreatophyte use.
It has been determined through study of aerial photographs
and the plants involved that phreatophytes used
5 percent of the 25 percent loss. The remaining
95 percent of seepage loss went to the groundwater without
quality degradation. This groundwater eventually went
back to the stream without quality degradation. Canal
lining could reduce this non-beneficial consumptive use
along the canal by 90 percent. The resulting water
conservation effort would save 0.25 x 0.05 x 0.90 =
about 1 percent of the total project water. This 1
percent of the water would then be available for dilution.
Total salt loading would be unchanged by such practice,
however.
Reduction of salt loading through reduced leaching
fractions (increased irrigation efficiency) must be
considered in regard to a specific soil. Where the
reduction in salt loading is dependent upon storage in
the soil below the root zone, it is doubtful as to
whether irrigation practices over a large region can be
tailored to the necessary precision. Table 5-4 gives
estimated reductions in leaching fractions for several
BMP's; reduction in salt loading is not so readily
predicted.
Where saline soils or rocks result in salt pickup, it
is expected that potential improvements will result in
a more significant reduction in salt load. From this
standpoint, pollution reduction potential must be
considered in terms of the quality change which would
occur to waters lost to the groundwater.
Since any potential quality change resulting from loss
of water to deep seepage is highly localized, it is
impossible to talk about the effectiveness of pollution
control measures in the general sense. We must, rather,
consider the reduction of water traveling a certain
pathway. Quality changes this water would undergo should
then be considered under local conditions. Table 5-5
presents typical volumes of water lost to deep seepage
under several systems.
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TABLE 5-5.
AVERAGE WATER LOSSES TO DEEP SEEPAGE
FOR IRRIGATION SYSTEMS
System
Conveyance Systems
Percent of Water Delivered
To This System Lost To
Deep Seepage
Range
Average
Canals, Laterals or
Head Ditches, Unimproved
Concrete Lined or Pipeline
3-40
0-10
20
5
Application Systems
Furrow or Border Irrigation
Furrow or Border With Good
Management, Irrigation
Scheduling
Sprinkler Irrigation*
Dead Level Irrigation
5-50
5-40
5-30
5-30
30
20
10-15
10-15
* Evaporation losses may average 5 to 10%
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5.8.2 Nitrates
Nitrates are associated with leaching of irrigated
fields. Control measures include better application
efficiency (reduced leachate) and better fertilizer
management. Better fertilizer management could
probably result in a 10 to 20 percent reduction of
nitrate concentrations in the leachate, although
supportive data is lacking. Reduced deep seepage
losses (improved irrigation efficiency) offer the
real key to reduced loading. Nitrate leaching is
especially problematic on sandy soils. Achieving
efficient surface irrigation can also be quite
problematic on these sandy soils. For these reasons,
reduction in nitrate loading can be closely related
to reductions in deep seepage losses. Without change
in fertilizer practices, significant changes in nitrate
concentration of percolating waters could not be
expected.
5.8.3 Sediment
The effectiveness of sediment control measures is
related to both the quantity of surface runoff and the
quality of that surface runoff. Any reduction in
quantity can be expected to reduce the tonnage of loss
to at least an equal percentage. In fact, reductions
in quantity typically result in significantly greater
reductions in total loading, since runoff velocities
are less. Several systems can totally eliminate the
pollutants associated with it—sediment, phosphorous,
and many pesticides. These systems are:
Tailwater return
Sprinkler irrigation
Dead level irrigation
Fitzsimmons et al (1977) and Lindeborg et al (1977)
present expected results and costs for sediment control
systems. These are presented in Table 5-6.
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TABLE 5-6. EXPECTED SEDIMENT LOSS REDUCTION FOR
SELECTED CONTROL PRACTICES ON TYPICAL
IRRIGATED FARMS IN THE MAGIC VALLEY
AND BOISE VALLEY (1)
Control Practice
Percent of "Typical"
Sediment Loss Retained
On Farm
Flow cut-back
Grass or grain strip
Sediment pond
Mini-basin
Sprinklers
30
50
67
90
100
(1) Lindeborg et al 1977.
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5.8.4 Other Pollutants Associated with Surface Runoff
Loading of phosphorous and pesticides associated with
sediment or surface runoff can probably be assumed to
be reduced at least as much as sediment loading by a
given practice, although very little data is available
at the current time.
5.8.5 Costs of Irrigated Agricultural Practices
Costs of agricultural practices vary from region to
region as well as with time. Justification of costs
should consider crop value, labor costs and others as
well as fixed costs. Consultation with local irrigation
system contractors, chemical dealers, arid agricultural
experts can be expected to produce accurate costs. Doanes
Agricultural Service publishes machinery operations costs
and other costs on an up-to-date basis for most regions.
Cost-effective analysis compares the equivalent annual
cost of potential best management practices with their
effectiveness in reducing pollutant load. Equivalent
annual cost includes:
Annualized capital cost
Annual operation and maintenance costs
Annual labor cost
Annual cost or benefit of altered crop yields
Annual cost or benefit of altered chemical
use or tillage operations.
Equivalency of units is required for comparison purposes.
Since the cost of most practices is dependent upon land
area, dollars/acre/year or dollars/hectare/year provide
a good comparison criteria. Assumptions may be required
to develop equivalent units. Lindborg et al (1977)
present an excellent economic analysis of sediment
control practices.
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Costs presented in the case study in Chapter 3.0
represent costs in northern Colorado in 1977. Efforts
should be made to localize costs prior to conducting
an analysis such as seen in Chapter 3.0.
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6.0 WATER LAW
Since the passage of the Federal Water Pollution Control
Act Amendments of 1972, all states are involved in water
pollution abatement or elimination efforts. In addition,
they are responsible for water resource allocation for
the many uses made of this resource. In the western
states where irrigated agriculture is a substantial and
important part of the economy, water quality laws and
water resource (or quantity) laws are having more impact
than ever before. Potential solutions for irrigated
agriculture water pollution problems are often times just
as dependent upon institutional and legal constraints,
as technical and financial capabilities.
6.1 WATER QUALITY LAW
Prior to the Federal Water Quality Control Act of 1965,
individual state water quality laws varied significantly
in purpose and scope and had little uniformity. Since
that time, and especially after passage of the Federal
Water Pollution Control Act Amendments of 1972 (PL 92-500)
the states have been following uniform Federal programs,
with minor variations from state to state. The objectives
of PL 92-500 were to provide Federal/State programs to
prevent, reduce, and ultimately eliminate water pollution.
It seeks to achieve fishable, swimmable waters, wherever
attainable by 1983.
Radosevich (1977) has separated the Act into five basic
components:
1. Water Quality Policy
2. Criteria for Pollution Control
a. Classification of Waters
b. Water Quality Standards
c. Effluent Discharge Standards
3. Control Activities
a. Permit System
b. Construction Grants and Programs
c. Public Participation in Planning and
Setting Standards
4. Sanctions and Enforcement Measures
5. Administrative Structure
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The Act identified two sources of pollution: point
and nonpoint. Point sources are end-of-pipe discharges
such as those from municipal sewage treatment plants,
industries, and some concentrated animal feeding
operations. Such sources are controlled through a
system of individual permits which prescribe types and
amounts of pollutants allowable in the discharge and
include implementation plans and provisions for self-
monitoring .
Nonpoint pollution sources pose a more difficult problem.
They are caused by precipitation runoff and/or seepage
which ultimately reaches waterways. Examples include:
surface runoff from urban areas, farms, or construction
areas; mine drainages, waste disposal areas; and septic
tanks.
Irrigation return flows of all types are considered to
be nonpoint sources according to 1977 amendments to
PL 92-500. Section 208 of the 1972 Act provides for
areawide waste treatment management plans which are
intended to address the nonpoint source problem and
establish programs for solution.
6.2 WATER ALLOCATION LAW
State water allocation laws began evolving during the
settlement of the eastern states and are still changing
today. With no guidelines to follow, eastern states
adopted England's common law riparian doctrine as a policy
for controlling waters. As settlement and development
moved westward, local customs, state laws, and individual
court cases determined water rights. From this, a doctrine
of prior appropriation evolved and was adopted by nearly
every western state. Many states' water law is a
combination of the two. In fact, each state has developed
its own unique system of both surface water and groundwater
laws. It is commonly held that water rising within or
occurring below a state's boundaries are under its
jurisdiction, unless subject to powers reserved for the
Federal Government. Figure 6-1 describes surface water
laws systems in the western states.
163
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LEGEND
APPROPRIATIONS
APPROPRIATIONS AND
RIPARIAN RIGHTS
FIG. 6-1. SURFACE WATER LAW SYSTEMS IN THE
WESTERN STATES
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6.2.1 Riparian Doctrine
This system follows the natural flow theory which
states that a landowner adjacent to a river or body
of water is entitled to use that water. The second
concept is that of reasonable use. Riparian landowners
can divert a reasonable amount of water with respect
to other riparians on the stream for beneficial use.
Hence, he is a correlative co-user with all other
riparians on the water source and priority of use
does not establish priority of right in times of
decreased flows. The right to use water is dependent
on the extent of development, not a fixed quantity
of water. Natural wants or domestic uses hold preference
of use over other uses. Reasonableness of use determines
preference between other uses: agriculture, industrial,
and recreational.
An important characteristic of a riparian water right
is that the right will continue as long as the land and
water source remain contiguous. Abandonment of the
right is nonexistent through nonuse or misuse; however,
misuse may result in a restriction of use and/or judgement
for damages.
Recent changes include establishment of:
1. A permit system (limitation on duration) for allocation
2. Administrative machinery to assess supplies and
requirements
3. Forfeiture (not to be confused with abandonment)
for nonuse
4. Minimum flow requirements
5. Greater flexibility and certainty in acquiring right.
Again, each state totally or partially following the
riparian doctrine is unique in its system of water allocation
and has adopted some or all of these changes in varying
degrees.
165
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6.2.2 Doctrine of Prior Appropriation
This system of water resource appropriation applies
the same principle as used in staking mining claims,
namely "first in time, first in right." Unlike the
riparian doctrine, a right to use water does not
automatically exist by virtue of location. A diversion
from a natural body of water is first needed. Second,
the water must be applied to a beneficial use. After
the diversion and beneficial use was completed, a
"water right" was created. Then each right acquired
a priority date. The priority of right and not
equality of right is the basis for distributing water.
This water right is a real property right and is commonly
described as an usufructuary right - a right to use the
resource. In addition, there is no absolute ownership
prior to diversion. After diversion and prior to
escaping the right holder's control, it is considered
personal property. Summarizing, this appropriated water
right:
1. Exists to a certain source
2. Is divertable (fixed and stated quantity)
3. Has a point of diversion to maintain conditions
4. Has a specified use
5. Identifies place of use
6. Implies annual time of use
7. Assures holder of an implied protection of quality.
There are several key elements contained in the doctrine
of prior appropriation which will be dealt with in relation
to irrigation return flow later in this chapter. The
discussion that,-follows attempts to summarize these key
elements. "" The actual process of water appropriation is
considered complete after three steps. First, an
application is filed with the proper state authority.
The appropriation will then be granted if unappropriated
water is available, if it will be put to beneficial use,
and if the public interest will not be adversely affected.
Finally, diversion and beneficial use must take place
before the applicant receives a right to the water.
166
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The concept of "beneficial use" for an irrigator
desc-ibes that amount of water necessary to irrigate
his land in a beneficial manner. Closely associated
to beneficial use is "duty of water." Duty of water,
often statutory in nature, refers to the quantity of
water in terms of reasonableness. It is that measure
of water which by careful management and use, without
wasteage, is reasonably required to be applied to any
given tract of land to raise ordinary crops ( Radosevich
1977). Waste is corollary to beneficial use, i.e.,
runoff is not considered waste, providing beneficial
use criteria is met. The farmer need not apply latest
technology nor limit return flow to zero. The test is
reasonableness, not mathematical exactness. Local
customes or methods can serve as a guide.
Preferences and priority to use are often confused.
The date of right is the distinguishing factor for
priority to use. Preference to use refers to type of
use given preference by laws - agricultural, domestic,
industrial, recreational, etc.
There are four ways through which loss of water rights
can occur:
1. Abandonment - failure to use the entire
appropriated right for a statutory period
of time with intention of abandonment.
2. Forfeiture - nonuse of water for statutory
term with intent being irrelevant.
3. Adverse possession - one person uses another
persons water who does nothing about it.
4. Condemnation - similar to police power by
preferred user or public entity.
167
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Another element in the doctrine of prior appropriation
concerns the transfer of water rights. In most states
a water right is appurtenant to the land on which it is
used thereby restricting the transfer of rights.
There are certain restrictions in transfers of rights
(Celnicker 1974), such as:
1. No other appropriation can be hurt.
2. While a change may be approved, conditions
necessary to prevent injury to others must
be included.
3, In some states transfer procedures are
provided by law.
4. Some state statutes specifically declare that
water rights cannot be detached from the lands,
place or purpose for which they are acquired,
only with certain exceptions.
5. Other states require that it become impractical
to beneficially or economically use water on
appurtenant land before transferring.
6. Inadequate measurement and poor records add to
costs and uncertainty.
These restrictions in transfers become important in the
question of efficient use of water and loss of water rights,
6.2.3 Ground Water Control Systems
Radosevich (1977) has categorized groundwater allocation
doctrines into four types commonly found in the western
states. Even though groundwater has been a source of
water for many uses for many years, some states have
within the past 10 years adopted regulations to control
this resource. This body of law and system of allocation
has developed for each state through case law, customs,
and established practices.
168
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The first doctrine is that of absolute ownership.
Simply stated, a landowner may withdraw any water from
beneath his land without liability to his neighbors.
A second system evolved out of disputes arising from
absolute ownership and incorporated the "rule of
reasonable use" from the Riparian Doctrine. It is
referred to as reasonable use and is more restrictive
than absolute ownership. Correlative rights is a third
concept which maintains that each landowner can make
reasonable use as long as the supply lasts. During
periods of short supply, percentage of overlying land
owned determines the amount of use. The last kind is
prior appropriation. As in surface water prior
appropriation, the source is allowed maximum development
with recognition and protection given prior users.
These four systems are shown in Figure 6-2 for the
western states.
6.2.4 Related Law
Several states have water users conjunctively using
surface and groundwaters. In order to protect interests
and insure continued resource development, augmentation
plans and groundwater management districts have been
established. Also, realizing the interconnection between
surface and groundwater, surface rights can be retired
if affected by groundwater resource allocation and
development.
While not directly related to allocation laws, two
concepts govern drainages on agricultural lands. The
common enemy rules says that a landowner can construct
dikes, etc., to protect his land from upland drainages
or uncontrolled runoff. Conversely, the rule of natural
drainage gives an advantage to the landowner above or
at higher elevations. Drainage from his land should
be allowed to follow the natural drainage patterns.
The most reasonable interpretation of both concepts
states that there can be reasonable interference by
either party to protect his property.
169
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LEGEND
APPROPRIATION
COMMON LAW RIPARIAN
CORRELATIVE RIGHTS
REASONABLE USE
FIG. 6-2. GROUND WATER LAW SYSTEMS IN THE WESTERN
STATES
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TABLE 6-1 CHARACTERISTICS OF WATER RIGHTS IN WESTERN STATES (Radosevich, 1977)
Arizona
California
Colorado
Idaho
Kansas
Montana
Nebraska
Nevada
New Mexico
North Dakota
Oklahoma
Oregon
South Dakota
Texas
Utah
Washington
Wyoming
Evidence
of Water
Right
Permit
Permit
Decree (SW)
Permit (GW)
License
Permit
Permit
Permit
Permit
Permit
Permit
Permit
Permit
License
Permit
Permit
Permit
Permit
Date
of
Priority
A
A
First
Step A
A
A
A
A
A
A
U
A
A
A
U
A
U
A
Preference
of
Use
1-2-3-4-5
1-2
1-2 over 5
1-2
1-2-5-6-3
None
1-2 over 5
None
None
1-2-5-6
None
1-2-4
1
1-5-2-4-3-
7-6
1-2
None
1-5
Allocation
Criteria
(Duty)
BU
B & RU
BU
1 cf s/A
l-2A-ft.
1A
1 Miners
inch/A
1 cfs/70A
3 A-ft/A
Conditions
& Needs
BU & Good
Agriculture
Practice
1 cf s/SOA
BU
BU
1 cfs/70A
3 A-ft/A
BU
Nature of Use
Reasonably
Necessary
1 cfs/70A
Drainage Appurtency
Rules
CE & CL Strict
RD Unlimited
CL None
CL Unlimited
CL
CE
CE
CL
CL
RD
RD Strict
CL Strict
CL
CL
CE
CE
Undecided Strict
Forfeiture
of Rights
by Nonuse
5 Years
3 Years
10 Years is evidence
of abandonment
5 Years
3 Years
10 Years is evidence
of abandonment
3 Years
5 Years
4 Years + I Year
after notice
3 Years
7 Years
5 Years
3 Years
10 Years
5 Years
5 Years
5 Years
A - Date of Application
U - Date of Beneficial Use
CE - Common Energy
CL - Civil Law
RD - Reasonable Discharge
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6.3 EFFECTS ON BEST MANAGEMENT PRACTICES
Both water quality laws and water quantity laws are
used in determining optimum management practices for
a particular area to control water pollution from
irrigated agriculture, specifically irrigation return
flows. Each state is unique in its system of water
pollution control and water rights allocation. There
are numerous issues involving interpretation of case
and statute law which should be analyzed on a state-
by-state basis before implementing best management
practices.
6.3.1 Water Quality Law Issues
The goal of the Federal Water Pollution Control Act
is to have fishable, swimmable waters where attainable
by 1983. Presumably, if all point and nonpoint source
pollution were controlled based on effluent standards
and water quality standards, this goal would be met.
However, many rivers in the arid weatern states are
used entirely for irrigation making the "fishable,
swimmable" criteria unnecessarily restrictive. Even
if that quality level could be attained, the quantity
of water remaining in a river after diversions during
irrigation seasons is sometimes too low to propagate
aquatic life or recreation. The phrase "where attainable"
has to be emphasized in the West.
A second question that many states have had to address
concerns the terms "nation's water" and "navigable
waters". Some states have included irrigation waters
in the definition of navigable waters, thereby applying
stream classifications and water quality standards to
irrigation waters. While it is reasonable to require
that return flows not degrade receiving waters, best
management practices should be tailored to the level of
water quality necessary to maintain an existing or
recommended classification. Here again, case-by-case
flexibility may reduce total pollution control costs.
172
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6.3.2 Water Quantity Law Issues
These water laws have evolved to regulate the use of
a limited resource in the western states. Although
there exist only two basic surface water law doctrines
and four groundwater law doctrines, each state has
developed its own allocation system using different
combinations of existing law. Also, case law in each
state is unique, causing still more diversity. The
technology involved with various best management
practices is available, but not necessarily implementable
in every state because of water rights laws restrictions
and limitations.
Best Management Practices implies that the predominant
pollution control strategy lies with management of the
irrigation practice itself as opposed to collecting
wastewater, applying treatment technology, and returning
it to the stream. Any control option which allows an
irrigator to divert his entire appropriated water right
each year, to use that water beneficially and
economically, and to discharge the return flow back
into the stream in such quality and quantity as required
by law, would not appear to pose any problem. The
conflict begins when a management practice consumptively
uses water belonging to a downstream user or endangers
the irrigator's continued right to that water, by water
management efficiency practices.
Many control options emphasize the efficient use of
water, the theory being that high levels of agricultural
production can be maintained using less water throughout
the system, consequently reducing the amount of return
flow- However, within the realm of the Prior Appropriation
Doctrine, there are disincentives to efficient water use.
The potential for loss of water rights through abandonment
and forfeiture encourages an irrigator to divert his total
appropriated amount of water. A farmer will not place
himself in a position of having forfeited a portion of his
water right through nonuse during years of average or
above average rainfall, knowing he will need his entire
appropriation in the event of a dry year. More lenient
173
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water rights transfer provisions insuring a farmer
access to his total appropriation when needed would
encourage greater water use efficiency in wet years.
It is feasible that efficient on-farm use of water
can result in additional quantities of water available
for use. Differing court opinions have confused the
answer to the question of whether an irrigator has
the right to use that additional quantity of water.
Although the general rule is that he can, the argument
of appurtenancy remains. "Commendable practices do
not in themselves create a legal right. Doctrine of
beneficial use precludes application of water gained
by conservation practices. Beneficial use is the
measure and the limit to the use of water." (Salt
River Valley Water Users Association vs. Kovacovich -
Arizona) ( Radosevich 1977). The case Reno vs. Richards
(ibid) states the general rule "... if one, by his own
efforts, adds to the supply of water in the stream,
he is entitled to the water which he has developed even
though an appropriator with more senior priority might
be without water."
While there may be a fine line differentiating irrigation
return flow and irrigation wastewater, certain case laws
clearly distinguish the two in terms of recapture and
reuse. Generally speaking, an individual irrigator can
recapture wastewater in his own property and reuse it
thereon. Also, a downstream user can appropriate
wastewater, but he cannot be assured that the upstream
user will continue to discharge. As a rule irrigation
districts can recapture return flow before it' leaves the
district's boundaries; however, this rule is not normally
extended to individuals. Reusing watewater may prevent
injury to a downstream user in terms of water quality,
but may cause injury because of decreased water quantity.
Both irrigators are affected in this case.
174
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In most states there are no explicit provisions
regarding the protection of water quality in water
allocation law. At best, the owner of the right has
a vested right to the quality as well as the quantity
which he has beneficially used. The quality to which
an appropriator has right is that which is sufficient
to "substantially fulfill the purpose for which his
appropriation was made." Case law is very limited
or non-existent with respect to private action based
on pollution caused by return flow. Any damage,
usually caused by many upstream users, must be
substantial. Prior to new state water quality laws,
any legal action must be brought by the downstream user.
175
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APPENDIX A
REFERENCES
176
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SUGGESTED REFERENCES
U.S. Department of Interior, Bureau of Reclamation,
1967. Water Measurement Manual, Second Edition,
U.S. Environmental Protection Agency and Colorado
State University, May 16-18, 1972. Managing
Irrigated Agriculture to Improve Water Quality.
Proceedings of National Conference on
Managing Irrigated Agriculture to Improve
Water Quality.
U.S. Environmental Protection Agency and Colorado
State University, May 16-19, 1977. Proceedings
of National Conference, Irrigation Return Flow
Quality Management.
U.S. Geological Survey, Water Supply Paper 1473,
Study and Interpretations of the Chemical
Characteristics of Natural Water.
177
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REFERENCES
CHAPTER 1.0 - INTRODUCTION
Miles, Don. 1977. "Salinity in the Arkansas Valley
of Colorado," Colorado State University and
U.S. Environmental Protection Agency.
Personal Communication. Toups Corporation and John
Erickson, Water Resource Associates, Scottsdale,
Arizona.
The Clean Water Act Showing Changes Made by the
1977 Amendments. U.S.G.P.O. Serial No. 95-12,
1977. (Federal Water Pollution Control Act
PL 92-500).
Toups Corporation. September, 1975. "Cost and
Effectiveness of Point Source Pollution Control
Options for Irrigated Agriculture," report to
National Committee on Water Quality.
U.S. Department of Commerce. 1969. Census of
Agriculture.
U.S. Department of Commerce.' 1974. Census of
Agriculture.
178
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REFERENCES
CHAPTER 2 - EVALUATION OF IRRIGATED AGRICULTURE
AS A POLLUTANT SOURCE WITHIN THE REGIONAL CONTENT
CHAPTER 3 - DEFINITION OF BEST MANAGEMENT
PRACTICES FOR IRRIGATED AGRICULTURE
Larimer-Weld Regional Council of Governments. 1978.
"Best Management Practices for Irrigated
Agricultural Pollution Control. Toups
Corporation.
Larimer-Weld Regional Council of Governments.
April 1977. Water Quality Impacts of Irrigated
Agriculture. Toups Corporation.
179
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CHAPTER 4.0 - POLLUTANTS ASSOCIATED
WITH IRRIGATION RETURN FLOW AND THEIR EFFECTS
UPON BENEFICIAL USE
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Three Cropping Sytems and Two Fertility Levels
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Broadbent, F.E., and H.D. Chapman. "A Lysemeter
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Buckman, H.O. and N.C. Brady. 1969. The Nature and
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September 1974.
U.S. Department of Agriculture, Agricultural Research
Service, U.S. Salinity Laboratory, Western Region,
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Irrigation Drainage Water, I. Effects of Irrigation
Water Composition, Leaching Fraction and Time of Year
on The Salt Compositions of Irrigation Drainage Waters."
Soil Science Society of America Proceedings, Vol. 37,
No. 5. J. 0 Rhoades, et.al.
184
-------
U.S. Department of Agriculture. 1954. Handbook 160
Diagnosis and Improvement of Saline and Alkali
Soils. U.S. Government Printing Office, Washington,
D.C.
U.S. Department of Agriculture, Soil Conservation Service.
1975. Agricultural Research Service. Control of
Water Pollution from Croplands. Vol. 1. "A Manual
for Guideline Development."
U.S. Department of Agriculture, Soil Conservation
Service, National Engineering Handbook on Sedimentation.
(For in-service use) 1968 ef.seq.
U.S. Department of Agriculture, Soil Conservation Service,
Special Projects Division, Denver, Colorado.
Irrigation Water Use, unpublished paper, Feb. -1975.
U.S. Environmental Protection Agency, Methods and Practices
for Controlling Water Pollution from Agricultural
Nonpoint Sources, EPA-430/9-73-015. October 1973.
U.S. Environmental Protection Agency. 1972. "The Effect
of Agricultural Pesticidse in the Aquatic Environment,
Irrigated Croplands, San Joaquin Valley." Pesticide
Study Series, Volume No. 6. Office of Water Programs,
Environmental Protection Agency, Washington, D.C.
U.S. Environmental Protection Agency. Water Quality Criteria
1972. A Report of the Committee on Water Quality
Criteria, Environmental Studies Board, National
Academy of Sciences, National Academy of Engineering.
Washington, D.C. 1972. U.S. Government Printing
Office: 1974-499-296.
Uttormark, O.E., J. D. Chapin, and K. M. Green. August
1974. "Estimating Nutrient Loadings of Lakes from
Nonpoint Sources." EPA 660/3-74-020. Environmental
Protection Agency. National Environmental Research
Center, Corvallis, Oregon.
Vom Rumker, R., E. W. Lawless, and A. F. Meiners. 1974.
Production, Distribution, Use, and Environmental Impact
Potential of Selected Pesticides.EPA 540/1-74-001.
Environmental Protection Agency Deputy Assistant
Administrator for Pesticide Programs.
185
-------
Weidner, R. B., A. G. Christiansen, and S. R. Weibel.
1969. "Rural Runoff as a Factor in Stream Pollution."
Journal Water Pollution Control Federation. 41:377-384
Wesseling, J. and Oster, J. D. July-August 1973.
"Response of Salinity Sensors to Rapidly Changing
Salinity." Soil Science Society of America Proceedings.
37:4:553.
186
-------
REFERENCES
CHAPTER 5- IRRIGATED AGRICULTURAL PRACTICES
AND POLLUTION CONTROL OPTIONS
ASCE. August 1974. "Irrigation Research to Increase
Production Without Environmental Damage." from
Contribution of Irrigation and Drainage to World Food
Food Supply.
Bondurant. J. A. 1970. "Get Double Use Of Our
Irrigation Water.: Idaho Farmer. Vol. 88, No. 6.
Bondurant. J. A., C. E. Brockway, and M. J. Brown.
1975. "Some Aspects of Sedimentation Pond Design."
presented at the National Symposium on Urban
Hydrology and Sediment Control (University of
Kentucky, Lexington, Kentucky. July 18-31, 1975).
Buckman, H.O., N. C. Brady. 1969. The Nature and
Properties of Soils. MacMillian.
Carter, D. L. 1976. "Guidelines for Sediment Control
in Irrigation Return Flows." Journal of
Environmental Quality. Vol. 5. April-June 1976.
Carter, D. L. May 1972. "Irrigation Return Flows in
Southern Idaho." Managing Irrigjated Agriculture
to Improve Water Quality. Proceedings of National
Conference on Managing Irrigated Agriculture to
Improve Water Quality sponsored by U.S. Environemental
Protection Agency and Colorado State University.
Carter, D.L. "Irrigation Return Flows in Southern
Idaho-" Snake River Conservation Research Center,
ARS, U.S.D.A.
Coleman, C. 1970 "How to Reclycle Runoff." World
Irrigation. Vol. 10, No. 3
Griddle, W. D., C. Kalisvaart. 1967. "Subirrigation
Systems." in Irrigation of Agricultural Lands.
American Society of Agronomy. 1967.
Davenport, L. A., W. D. Lembko, and B. A. Jones. March
1973. "Nitrate Reduction in the Vicinity of Tile
Drains." Illinois Water Resources Center, Urbana
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187
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David, M. L. and G. M. Manner. October 6-8, 1971.
"Economic Evaluation of Irrigation in Humid Areas."
Paper presented at ASCE Specialty Conference,
Lincoln, Nebraska.
Davis, J. R. and W. E. Hart. 1963. "Efficiency
Factors in Sprinkler Irrigation Design." Sprinkler
Irrigation Association. Open Technical Conference
Proceedings.
De Remer, E. D. November 1970. "Starting with Trickle
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Fitzsimmons, D. W. et.al. "On-Farm Methods for Controlling
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Proceedings. J. P. Law and G. V. Skogerboe, Eds.
May 1977, Colorado State University.
Frost, K. R. 1963. Twelve Years of Sprinkler Irrigation
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Edminster, Barnes, Soil and Water Conservation
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Gear, R. D., A. S. Dransfield, and M. D. Campbell.
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Irrigation of Agricultural Lands, American Society
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Hedlund, J. D. December 1975. Meeting Future Water
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Houck, L. E. 1956. Irrigation Engineering.
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Jensen, M. E. 1975. Scientific Irrigation Scheduling for
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189
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Kansas State University, Cooperative Extension Service.
1973. North Kansas Irrigation Demonstration Farm.
Annual Report. D. R. Hay.
King, L. G. and R. J. Hanks. 1973. "Irrigation Management
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EPA R2-730265. U. S. Environmental Protection Agency.
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"Economic Analysis of On-Farm Methods for
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National Conference on Irrigation Return Flow
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Lyons, C. G., Jr. Winter 1972. "Trickle Irrigation...
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Pages 3-4.
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190
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Powell, G. M.f M. E. Jensen, and L. G. King. 1972.
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St. Amant, P. and L. A. Beck. October 1970. "Nitrate
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the Irrigation and Drainage Division ASCE. Vol. 94,
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Schwab, G. 0. R. K. Frevert, T. W. Edminister, and K. K.
Barnes. 1966. Soil and Water Conservation Engineering.
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Skogerboe, G. V. and W. R. Walker. "Evaluation of Canal
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EPA-R2-72-047. U.S. Environmental Protection Agency.
1972.
Skogerboe, G. V., W. R. Walker, J. H. Taylor, and R. S.
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U.S. Environmental Protection Agency. National Environ-
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Stewart, B. A.,D- A. Woolhiser, W. H. Wishchmeier, J. H.
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Pollution from Cropland. Vol. 1.
Toups Corporation. 1975. Cost and Effectiveness of Point
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U.S. Bureau of Reclamation, Engineering and Research Center,
Denver, Colorado. "Shut Off the Water, The "Root Zone
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191
-------
U.S. Department of Agriculture, Soil Conservation Service,
Agricultural Reserach Service. November 19/b.
Control of Water Pollution from Cropland. Vol. i
U.S. Department of Agriculture, Soil Conservation Service,
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July 1973. 1969 Census of Agriculture. Vol. VI,
"Drainage of Agricultural Lands."
U.S. Department of Commerce, Bureau of the Census. July
1973. 1969 Census of Agriculture. Vol IV, "Irrigation."
U.S. Department of Interior, Bureau of Reclamation.
Possibility of Reducing Nitrogen in Drainage Water
by On-Farm Practices. 13030 ELY 5-72-11.
U.S. Department of Interior, Bureau of Reclamation. 1975.
Water and Resource Accomplishments, 1974. Summary
Report.
University of California, Agricultural Extension Service.
April 1972. An Analysis of Corn Production Costs in
California. A. D. Reed.
University of California. November 1964. Agricultural
Extension Service, AXT-161, "Guides to Selecting An
Economical Surface Irrigation System."
Utah State University. December 1974. Energy Inputs to
Irrigation. J. C. Batty, S. N. Hamad, and J. Keller.
Van Schilfgaarde. J. L., Bernstein, J. D. Rhoades, and
S. L. Rawlins. September 1974. "Irrigation
Management for Salt Control." ASCE Journal of the
Irrigation and Drainage Division. Vol. 103, No. IR3.
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Production,Distribution, Use and Environmental
Impact of Selected Pesticides. EPA 540/1-74-001. 1974.
Von Rumker, R, G. L. Kelso. July 1975. A Study of the
Use of Pesticides in Agriculture. EPA-540/9-75-025.
U.S. Environmental Protection Agency. Deputy
Assistant Administrator for Pesticide Programs.
Williardson, L. S., G. D. Meek, G. L. Dickey, and J. W.
Bailey. January-February 1972. "Nitrate Reduction
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192
-------
REFERENCES
CHAPTER 6.0 - WATER LAW
Celnicker, Arnold. "State Water Laws and Pollution
Caused by Irrigation Return Flow." Environmental
Protection Agency, Office of Enforcement,
National Field Investigations Center, Denver,
Colorado. September 1974.
Radosevich, George E. and Gaylord Skogerboe.
"Achieving Irrigation Return Flow Quality
Control Through Improved Legal Systems."
(Draft Copy) Resources Administration and
Development, Inc., Fort Collins, Colorado.
Radosevich, George E. 1977. "Interface of Water
Quantity and Water Quality Laws in the West."
Proceedings. National Conference on Irriga-
tion Return Flow Quality Management. Fort
Collins.
193
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APPENDIX B
GLOSSARY
194
-------
APPENDIX B
GLOSSARY
Climate: The sum total of all atmospheric or meteorological
influences, principally temperature, moisture, wind,
pressure, and evaporation, which combine to characterize
a region and give it individuality by influencing the
nature of its land forms, soils, vegetation, and land
use.
Consumptive use: The water used by plants in transpiration
and growth, plus water vapor loss from adjacent soil
or snow, or from intercepted precipitation in any
specified time. Usually expressed as equivalent depth
of free water per unit of time.
Denitrification: The biochemical reduction of nitrate or
nitrate to gaseous nitrogen either as molecular nitrogen
or as an oxide of nitrogen.
Erosion: (i) The wearing away of the land surface by running
water, wind, ice, or other geological agents, including
such processes as gravitational creep. (ii) Detachment
and movement of soil or rock by water, wind, ice, or
gravity. The following terms are used to describe
different types of water erosion:
accelerated erosion: erosion much more rapid
than normal,natural, geological erosion,
primarily as a result of the influence of the
activities of man or, in some cases, of animals.
gully erosion: 'the erosion process whereby water
accumulates in narrow channels and, over short
periods, removes the soil from this narrow area
to considerable depths, ranging from 1 or 2 feet
to as much as 75 to 100 feet.
natural erosion: wearing away of the earth's surface
by water, ice, or other natural agents under
natural environmental conditions of climate,
vegetation, etc., undisturbed by man. Synonymous
with geological erosion.
normal erosion: the gradual erosion of land used
by man which does not greatly exceed natural erosion.
rill erosion: an erosion process in which numerous
small channels of only several inches in depth are
formed; occurs mainly on recently cultivated soils.
sheet erosion: the removal of a fairly uniform
layer of soil from the land surface by runoff water.
splash erosion: the spattering of small soil par-
ticles caused by the impact of raindrops on very
wet soils. The loosened and separated particles
may or may not be subsequently removed by surface
runoff.
195
-------
Glossary continued - 2
Eutrophication; A means of aging of lakes whereby aquatic
plants are abundant and waters are deficient in oxygen.
The process is usually accelerated by enrichment of
waters with surface runoff containing nitrogen and
phosphorus.
Evapotranspiration: The combined loss of water from a given
area, and during a specified period of time, by evap-
oration from the soil surface and by transpiration
from plants.
Fertilizer; Any organic or inorganic material of natural
or synthetic origin which is added to a soil to supply
certain elements essential to the growth of plants.
Fixation: The process or processes in a soil by which
certain chemical elements essential for plant growth
are converted from a soluble or exchangeable form to
a much less soluble or to a nonexchangeable form;
for example, phosphate "fixation." Contrast with
nitrogen fixation.
Groundwater: Water that fills all the unblocked pores of
underlying material below the water table, which is
the upper limit of saturation.
Herbicide; A chemical substance used for killing plants,
especially weeds.
Infiltration Rate: A soil characteristic determining or
describing the maximum rate at which water can enter the
soil under specified conditions, including the presence
of an excess of water.
Irrigation Efficiency; The ratio of the water actually
consumed by crops on an irrigated area to the amount
of water diverted from the source onto the area.
Irrigation Methods: The manner in which water is artificially
applied to an area. The methods and the manner of
applying the water are as follows:'
border strip; the water is applied at the
upper end of a strip with earth borders to
confine the water to the strip.
check-basin; the water is applied rapidly to
relatively level plots surrounded by levees. The
basin is a small check.
corrugation: the water is applied to small,
closely-spaced furrows, frequently in grain.and
forage crops, to confine the flow or irrigation
water to one direction.
196
-------
Glossary continued - 3
flooding: the water is released from field
ditches and allowed to flood over the land.
furrow: the water is applied to row crops in
ditches made by tillage implements.
sprinkler: the water is sprayed over the soil
surface through nozzles from a pressure system.
subirrigation: the water is applied in open
ditches or tile lines until the'water table is
raised sufficiently to wet the soil.
wild-flooding: the water is released at high
points in the field and distribution is uncon-
trolled.
Leaching; The removal of materials in solution from the soil.
Nitrification: The biochemical oxidation of ammonium to nitrate.
Nitrogen fixation; The conversion of elemental nitrogen (N2)
to organic combinations or to forms readily utilizable in
biological processes.
Percolation, soil water: The downward movement of water through
soil. Especially, the downward flow of water in saturated
or nearly saturated soil at hydraulic gradients of the
order of 1.0 or less.
Pesticide: A chemical agent used to control pests.
Plant nutrients: The elements or groups of elements taken
in by a plant which are essential to its growth and
used in elaboration of its food and tissues. Includes
nutrients obtained from fertilizer ingredients.
Runoff; That portion of the precipitation on an area which
is discharged from the area through stream channels.
That which is lost without entering the soil is called
surface runoff and that which enters the soil before
reaching the stream is called ground water runoff or
seepage flow from ground water. (In soil science
"runoff" usually refers to the water lost by surface
flow; in geology and hydraulics "runoff" usually includes
both surface and subsurface flow.)
Sediment; Solid material, both mineral and organic, that is in
suspension, is being transported, or has been moved from
its site or origin by air, water, gravity, or ice and has
come to rest on the earth's surface either above or
below sea level.
197
-------
Glossary continued - 4
Sodium-adsorption ratio (SAR): =
where the cation concentrations are in milliequivalents
per litter.
Soil; (i) A dynamic natural body on the surface of the
earth in which plants grow, composed of mineral and
organic materials and living forms. (ii) The collection
of natural bodies occupying parts of the earth's surface
that support plants and that have properties due to
the integrated effect of climate and living matter
acting upon parent material, as conditioned by relief,
over periods of time.
Soil alkalinity: The degree or intensity of alkalinity of
a soil,expressed by a value > 7.0 on the pH scale.
Soil conservation: A combination of all management and
land use methods which safeguard the soil against
depletion or deterioration by natural or by man-
induced factors.
Soil management: The sum total of all tillage operations,
cropping practices, fertilizer, lime, and other treatments
conducted on or applied to a soil for the production of
plants.
Soil salinity: The amount of soluble salts in a soil, expressed
in terms of percentage parts per million, or other
convenient ratios.
Water table: The upper surface of ground water or that
level below which the soil is saturated with water;
locus of points in soil water at which the hydraulic
pressure is equal to atmospheric pressure.
198
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APPENDIX C
PESTICIDES
199
-------
APPENDIX C
PESTICIDES
Agricultural herbicides: types, transport modes, toxicities, and persistence in soil
Common Names of
Herbicides
Alachlor
Ametrync'
Amitrolc
Asulam
Atrazinc
Harban
Ucnef'in
Bensulidc
Bcntazon
Bii'enox
Bromacil
Broinoxynil
Butylale
Cacodylic Acid
CDAA
CDliC
Chlorambcn
Chlorbromuron
Cliloroxuron
Chlorpropluun
Cyanazine
Cycloatc5
2,4-D Acid
2, 4-D Aminc
2,4-D I-sler
Dalapon
2,4-DB
DC'PA
Diallatc
Dieamba
Dichlobenil
Dinitraminc
Dinoseb
Diphcnumid
DU]uat
Diuron
DSMA
Fndothall
I:PTC
I'cnac
l''cnuron
Duomcturon
riuorodilen
Glyphosaie
Isopropalin
Linuron
MBR 825 1
MCPA
Metribu/.in
Molinatc
Monuron
MSMA
Naptalam
Chemical Class1
AM
TZ
TZ
CB
TZ
CB
NA
AM
DZ
AR
DZ
NT
CB
AS
AM
CB
AR
UR
UR
CB
TZ
CB
PO
PO
PO
AL
PO
AR
CB
AR
NT
NA
PH
AM
CT
UR
AS
PH
CB
AR
UR
UR
AR
AL
NA
UR
AM
PO
TZ
CB
UR
AS
AR
Predominant
Transport
Mode2
SW
sw
W
W
SW
S
S
S
W
S
W
SW
S
S
W
SW
W
SW
S
SW
SW
SW
W
W
S
W
S
S
S
W
S
S
SW
W
S
S
S
W
SW
SW
W
SW
S
S
S
S
SW
SW
W
W
SW
S
W
Toxicity3
Rat, Acute
OralLD50,
mg/kg
1200
1110
2500
>8000
3080
1350
800
770
1100
4600
5200
250
4500
700
850
3500
2150
3700
1500
334
2000
370
370
500-875
6590
300
3000
395
1028
3160
3000
5
970
400
3400
600
38
1360
1780
6400
7900
15000
4320
5000
1500
633
650
1930
501
3500
700
1770
Fish4 LC ; , ,
mg/lit er
2.3
Low toxicity
>50
6 5000
12.6
7 1.3
6 0.03
0.72
190
1.8
70
0.05
4.2
e
8>40
2.0
4.9
6 7.0
0.56
8>15
6 10
4.9
4.5
9>50
8>15
8 4.5
MOO
4.0
>500
5.9
35
10-20
6.7
7.'°0.4
25.0
12.3
>60
>15
1.15
19.0
7.5
53
10>60
0.18
Low toxicity
Toxic
16.0
312
10.0
>100
0.29
1.8
>15
>180
Approximate
Persistence
in Soil,
days
40-70
30-90
15-30
25-40
300-500
20
120-150
500-700
40-60
700
40-80
2040
2040
40-60
300400
120-260
120-220
10-30
10-30
10-30
15-30
400
120
60-180
90-120
15-30
90-180
>500
200-500
30
350-700
30-270
150
150
120
30-180
150-200
80
150-350
20-60
*"Control of Water Pollution From Cropland," Vol. I A Manual for
Guideline Development. Agricultural Research Services, U.S D A
and Office of Research and Development, U.S. EPA, November'1975
200
-------
Agricultural herbicides: types, transport modes, toxicities, and persistence in soil-(continued)
Common Names of
Herbicides
Nitralin
Nitrofen
Oryzalin
Paraquat
Pebulate5
Phenmedipham
Picloram
Profluralin
1'rometone
Prometryne
Pronamide'
Propachlor'
Propanil5
Propazine
Propliam
Pyrazon
Silvcx
Simazinc
2,4,5-T
TCA
Terbatil
Terbutrync5
"riallatc5
Trifluralin
Vcrnolate
Chemical Class1
NA
PO
AM
CT
CB
CB
AR
NA
TZ
TZ
AM
AM
AM
TZ
CB
DZ
PO
TZ
PO
AL
DZ
TZ
CB
NA
CB
Predominant
Transport
Mode2
S
S
S
S
S
S
w
S
S
S
S
w
S
S
w
w
sw
S
w
w
w
sw
S
S
sw
Toxicity'
Rat, Acute
OralLD,0,
mg/kg
2000
2630
> 10000
150
921
2000
8200
2200
1750
3750
5620
710
1384
5000
5000
2500
375
5000
300
3370
5000
2400
1675
3700
1625
Fish4 LC, „ ,
me/liter
Low toxicity
Toxic
Low toxicity
6 400
"6.3
10 20
2.5
Toxic
9>1.0
9>1.0
1.3
> 10.0
>100
6 32
12 40
9 0.36
5.0
0.5-16.7
13 >2000
14 86
Low toxicity
4.9
6 0.1
9.6
Approximate
Persistence
in Soil,
days
>500
50-60
100
550
320-640
>400
30-90
60-270
30-50
1-3
200400
20-60
30-60
200-400
20-70
700
20-70
3040
120-180
50
Chemical type designations: AL, aliphatic acids; AM, amides and anilidcs; AR, aromatic acids and esters; AS, arsenicals; CB.
carbamates and thiocarbamates; CT. cationics; DZ, diazines; NA, nitroanilines; NT, nitriles;JPH, phenols and dicarboxylic acids;
PO.phenoxy compounds; TZ, triazines and triazoles; UR^, ureas.
2 Where movement of herbicides in runoff from treated fields occurs, j^denotes those chemicals that will most likely move
primarily with the sediment,_W_ denotes those that will most likely move primarily with the water, and j>W denotes those that will
most likely move in appreciable proportion with both sediment and water.
3 Expressed as the lethal dose, or lethal concentration, to 50% of the test animals (LDS „ or LC, 0, respectively).
4 48- or 96-hour LC5 0 for bluegills or rainbow trout, unless otherwise specified.
Trade name; no corresponding common name exists.
* 24-hour LCS0.
For goldfish.
10
11
12
13
14
For killifish.
For spot .
For mullet.
For harlequin fish.
For catfish.
For sunfish.
201
-------
Often-used trade-name synonyms of agricultural herbicides
Trade Name
AAtrcx
Alanap
Ainiben
Amino Triazole
Avadex
Avadex BW
Balan
Banvel
Basanite
Betanal
Betasan
Baladcx
Bromcx
Butoxonc
Butyrac
Caparol
Carbyne
Casoron
Chloro-IPC
C1PC
Cobex
Dacthal
Destun
DNBP
Dowpon
Dymid
Enidc
Kptam
Eradicanc
Far-Go
Purloe
Ipran
IPC
Karmex
Name in
Table 8a
Atrazine
Naptalam
Chloramben
Amitrole
Diallate
Triallate
Benel'in
Dicamba
Dinoseb
Phenmedipham
Bcnsulidc
Cyanazine
Chlorbromuron
2,4-DB
2,4-DB
Prometryne
Barban
Dichlobenil
Chlorpropham
Chlorpropham
Dinitramine
DCPA
MBR 825 1
Dinoseb
Dalapon
Diphenamid
Diphenamid
EPTC
EPTC
Triallate
Chlorpropham
Terbutryn
Propham
Diuron
Trade Name
Lasso
Lorox
Maloran
Milogard
Modown
Norex
NPA
Ordram
Paarlan
Planavin
Prcfar
Preforan
Premerge Dinitro
Princep
Pyramin
Ramrod
Randox
Ro-Nect
Ryzelan
Roundup
Sencor
Sinbar
Sinox
Soyex
Stain F-34
Surflan
Sutan
Telvar
Tenoran
Tordon
Trellan
Vegadex
Vernam
Name in
Table 8a
Alachlor
Linuron
Chlorbromuron
Propazine
Bit'enox
Chloroxuron
Naptalam
Molinatc
Isopropalin
Nitralin
Bensulide
I'luoroditen
Dinoseb
Simazine
Pyrazon
Propachlor
CDAA
Cycloatc
CJryzalin
Glyphosate
Metribuzin
Terbacil
Dinoseb
Fluoroditen
Propanil
Oryzalin
Butylate
Monuron
Chloroxuron
Picloram
Trifluralin
CDEC
Vernolate
202
-------
Agricultural insecticides and miticides: types, transport modes, and toxicities
Common Names of
Insecticicles-Miticides
Aldicarb5
Aldrin
Allethrin
Azinphos ethyl
Azinphos methyl
Benzene hexachloride
Binapacryl
Bux6
Carbaryl
Carbofuran5
Carbophenothipn
Chlorbenside
Chlordane
Chlordimeform
Chlorobenzilatc6
Chlorpyrifos
DDT
Demeton5
Diazinon5'6
Dicofol*
Dicrotophos
Dicldrin
Dimethoate
Dioxathion
Disulfoton
Kndosulfan
lindrin
EPN
Ethion
F.thoprop
Fcnsulfothion5
Fonofos
Heptachlor
Landrin
Lindane
Malathion
Metaldehyde
Mcthidathion
Mcthomyl
MethoxychlOr
Methyl domcton6
Methyl parathion6
Mevinphos
Mexacarbatc
Monocrotophos
Naled
Ovex
Oxythioquinox
Parathion
Perthane6
Phoratc5
Pliosalone
Phosmet6
Chemical Qass1
CB
OCL
PY
OP
OP
OCL
N
CB
CB
CB
OP
S
OCL
N
OCL
OP
OCL
OP
OP
OCL
OP
OCL
OP
OP
OP
OCL
OCL
OP
OP
OP
OP
OP
OCL
CB
OCL
OP
O
OP
CB
OCL
OP
OP
OP
CB
OP
OP
S
S
OP
OCL
OP
OP
OP
Predominant
Transport
Mode2
W
S
S
S
S
S
U
S
sw
W
S
S
S
W
S
U
S
W
sw
S
W
S
W
S
S
S
S
S
S
U
sw
S
S
sw
S
W
W
U
U
S
W
sw
W
sw
W
S
S
S
S
S
sw
S
S
Toxicity
Rat, Acute
OralLD,n,
mg/kg
0.93
35
680
7
11
1000
120
87
500
8
10
3000
335
162
700
97
113
2
76
684
22
46
185
23
2
18
7.3
8
27
61.5
2
8
90
178
88
480
1000
25
17
5000
65
9
4
22.5
21
250
2000
1100
4
>4000
1
96
147
Fish4LC,,,,
nig/liter
0.003
0.019
0.019
0.010
0.79
0.04
0.29
1.0
0.21
0.23
0.010
1.0
0.71
0.020
0.002
0.081
0.030
0.10
8.0
0.003
9.6
0.014
0.040
0.001
0.0002
0.10
0.23
1.0
1 0.15
0.03
0.009
0.95
0.018
0.019
> 100.0
~0.9
0.007
4.0
1.9
0.017
1.73
7.0
0.078
0.70
0.096
0.047
0.007
0.0055
3.4
8 0.03
liO'i
-------
Agricultural insecticides and miticides: types, transport modes, and toxicities-(continued)
Common Names of
Insecticides-Miticides
Phosphamidon
Propargite6
Propoxur
IDE
TEPP
Tetrachlorvinphos
Tetradifon
Thionazin
Toxaphene
Trichlorfon
Chemical Qass1
OP
s
CB
OCL
OP
OP
OCL
OP
OCL
OP
Prcdominsnt
Transport
Mode2
W
U
W
S
W
s
sw
W
s
W
Toxicity3
Rat, Acute
Oral LD -
vsioi x-f 5 (i }
mg/kg
11
2200
95
3360
1
4000
14000
12
69
275
Fish4 LCS „ ,
mg/liter
8.0
0.03
9 0.025
0.009
9 0.39
0.53
1.10
7 0.10
0.003
0.16
Chemical type designations: CB. caibamates; N, miscellaneous nitrogenous compounds; O, cyclic oxygen compounds; OCL,
organochlorines; OP, organophosphorus compounds;_PY, synthetic pyrethrin;_S, aromatic and cyclic sulfur compounds.
2 Where movement of insecticides in runoff from treated fields occurs, jS denotes those chemicals that will most likely move
primarily with the sediment,^denotes those that will most likely move primarily with the water, SW denotes those that will most
likely move in appreciable proportion with both sediment and water, and IJ denotes those whose predominant mode of transport
cannot be predicted because properties are unknown.
3 Expressed as the lethal dose, or lethal concentration, to 50% of the test animals (LD5 „ or LC5 0, respectively).
48- or 96-hour LCS „ for bluegills or rainbow trout, unless otherwise specified.
5 Registered as both insecticide and nematicide. Nematodes are controlled only on limited acreage and predominantly in the
Southern states, but application rates when used as nematicides are 2- or 3-fold higher than when used as insecticides.
6 Trade name; no corresponding common name exists.
7 24-hour LC5n
8 For killifish
9 For minnows
204
-------
Often-used trade-name synonyms of agricultural insecticides and miticides
Trade Name
Acaraben
Azodrin
Basudin
Baygon
BHC
Bidrin
Cygon
Dasanit
ODD
Dclnav
Dibrom
Dlmecrom
Uipterex
Di-Syston
Dursban
Dyfonate
Dylox
Ethyl Guthion
l-undai
1 uradan
Galecron
Gamma-BHC
Gardona
Guthion
Name in Table 9a
Chlorobenzilate
Monocrotophos
Diazinon
Propoxur
Benzene Hexachloride
Dicrotophos
Dimethoate
1'ensulfothion
TDE
Dioxathion
Naled
Phosphamidon
Trichlorfon
Disulfoton
Oilorpyrifos
honofos
Trichlorfon
Azinphos ethyl
Chlordimcform
Carbofuran
Chlordimeform
Linda nc
Totrachlorvinphos
Azinphos methyl
Trade Name
Imidan
Kelthane
Lannate
Maria te
Mcta-Systox
Mocap
Morestan
Morocide
Ncguvon
Omite
Phosdrin
Prolate
Rabon
Sevin
Spectracide
Supracidc
Systox
Ted ion
Temik
Thimct
Thiodan
Trithion
Zectran
Zinophps
Zolone
Name in Table 9a
Phosmct
Dicofol
Mctliomyl
Mcthoxychjor
Methyl demeton
Ethoprop
Oxythioquinox
Binapaeryl
Irichlorfon
Propargite
Mevinphos
Phosmet
Tetrachlorvinphos
Carbaryl
Diazinon
Mcthidathion
Demeton
Tetradifon
Aldicarb
Phorate
Endosulfan
Carbophcnothion
Mexacarbate
Thionazin
Phosalonc
205
-------
Agricultural fungicides: transport modes and toxicities
Common Names of F'ungieidcs
Anilazine
Benomyl
Captafol
Captan
Carboxin
Chloranil
Chloroncb
Cyclohcximide
DCNA
Dichlone
Dichlozoline
Dinocap
Dodine
ETMT
Fenaminosulf
F'crbam
Folpet
Maneb
Metiram
Nabam
Ocycarboxin
Parinol
PCNB
SMDC
Thiram
TPTH
Zincb
Ziram
Predominant Transport Mode1
S
S
S
S
SW
W
U
W
S
S
TJ
S
W
u
W
SW
S
S
u
W
W
u
S
W
S
u
S
W
Toxicity2
Rat, Acute Oral LDjQ, mg/kg
2710
>9590
5000
9000
3200
4000
11000
2.5
4040
1300
3000
980
1000
2000
60
>17000
>10000
6750
6400
395
2000
>5000
1650
820
375
108
>5200
1400
Fish LC50, mg/liter
0.015
0.5
4 0.031
0.13
2.2
5.0
>4200.0
1.3
0.047
5 0.14
0.9
23.0
4 12.6
6 1.56
7 1.0
>4.2
4 21.1
8 ~5.0
0.7
7 1.0
4 0.79
0.5
4 1.0
Where movement of fungicides in runoff from treated fields occurs, S denotes those chemicals that will most likely move pri-
marily with the sediment, W denotes those that will most likely move primarily with the water, SW denotes those that will most likely
move in appreciable proportion with both sediment and water, and U denotes those whose predominant mode of transport cannot be
predicted because properties are unknown.
Expressed as the lethal dose, or lethal concentration, to 50% of the test animals
48- or 96-hour LCso for bluegills or rainbow trout, unless otherwise specified.
F'or catfish
For harlequin fish
For mullet
or
, respectively).
F'or fathead minnow
206
-------
Often-used trade-name synonyms of agricultural fungicides
Trade Name
Actidione
Ben late
Botian
Cyprex
DCNA
Demosan
Dilolatan
Dexon
Dyrene
Karathanc
Parnon
Name in Table lOa
Cycloheximide
Benomyl
DCNA
Dodine
Botran
Chloroneb
Captafol
Fenaminosulf
Anilazinc
Dinocap
Parinol
Trade Name
Phaltan
Phygon
Plantvax
Polyram
Spergon
Terrachlor
TMTD
Vapam
Vitavax
Name in Table lOa
Folpet
Dichlonc
Oxycarboxin
Metiram
Chloranil
PCNB
Thiran)
SMDC
Carboxin
207
-------
Major crops and principal pesticides registered for use on them throughout the United States
Crop
Alfalfa
Corn
Cotton
Fruit crops
Herbicides
Benefin
Chlorpropham
2, 4-DB
Diallate
Dinoseb
Diuron
Atrazine
Butylate
CDAA
CDEC
Chloramben
Cyanazine
2,4-D
Bensulide
Cacodylic acid
DCPA
Dintramine
Diphenamid
Diuron
DSMA
Endothall
Bromacil
Chlorpropham
2,4-D
Dalapon
DCPA
Pichlobenil
Dinoseb
Diphenamid
EPIC
MCPA
Nitralin
Propham
Simazine
Trifluralin
Dalapon
DCPA
Dicamba
Dinoseb
Diuron
EPTC
Linuron
Paraquat
Prometryne
Propachlor
Simazine
EPTC
Fluometuron
MSMA
Nitralin
Paraquat
Promotryne
Propachlor
Trifluraiin
Diuron
EPTC
Naptalam
Paraquat
Simazine
Tcrbacil
Trifluralin
Insecticides and miticidcs
Azinphos methyl
Carbaryl
Carbofuran
Carbophenothion
Demeton
Diazinon
Dimcthoate
Disulfoton
Endosulfan
Malathion
Bux
Carbaryl
Carbofuran
Carbophenothion
Chlordane8
Diazinon
Disulfoton
EPN
Ethoprop
Fcnsulfothion
Fonofos
Aldicarb
Azinphos methyl
Carbaryl
Carbophenothion
Chlordanea
Chlordirncform
Chlorobenzilate
Demeton
Diazinon
Dicofol
Dicrotophos
Dimethoate
Disulfoton
Endosulfan
Endrin
Azinphos methyl
BHC
Binapacryl8
Carbaryl
Carbophenothion
Chlordane'
Chlordirncform
Chlorobenzilate
Demeton
Diazinon
Dicofol
Dimethoate
Dioxathion
Endosulfan
EPN
Ethion
Methomyl
Methoxychlor
Methyl parathion
Mevinphos
Naled
Parathion
Phorate
Phosmct
Toxaphene
Trichlorfon
Heptachlora
Landrin
Malathion
Methomyl
Methoxychlor
Methyl parathion
Mevinphos
Parathion
Phoratc
Tetrachlorvinphos
Toxaphene
Trichlorfon
EPN
Ethion
Malathion
Mcthidathion
Methyl parathion
Monocrotophos
Naled
Parathion
Phoratc
Phosphamidon
Propargite
Toxaphene
Trichlorfon
Lindane
Malathion
Metaldchyde
Methoxychlor
Methyl parathion
Mevinphos
Naled
Ovex
Oxythioquinox
Parathion
Perthane
Phosalone
Phosmet
Phosphamidon
Propargite
Tetrachlorvinphos
Tetradifon
Toxaphene
208
-------
Major crops and principal pesticides registered for use on them throughout the United States-Continued
Crop
Peanuts
Rice
Small gtainsb
Sorghum
Soybeans
Sugar beets
Sugarcane
Herbicides
Alachlor Diphenainid
Bcnefin Naptalam
2, 4-DB Nitralin
Dinitramine Vernolatc
Dinoseb
Chlorpropham Propanil
2, 4-D Silvex
MCPA 2, 4, 5-T
Molinate
Bromoxynil Dicamba
2, 4-D Dinoseb
Diallate MCPA
Atrazine Dicamba
Bifenox Linuron
CDAA Paraquat
2, 4-D Propachlor
Dalapon Propazine
Alachlor Dinoseb
Barban Diphenainid
Bifenox Fluorodifen
CDEC Linuron
Chloramben Naptalam
Chloroxuron Nitralin
Chlorpropham Paraquat
Dalapon Trifluralin
2, 4-DB Vernolate
DCPA
Dinitramine
Barban Pebulate
Chlorpropham Phenmedipham
Cycloate Propham
Dalapon Pyrazon
Diallate Trifluralin
EPTC
Paraquat
Ametryn Fluometuron
Atrazine Simazine
2, 4-D Trifluralin
Dalapon
Fcnac
Insecticides and miticides
Carbaryl
Diazinon
Fensulfothion
Fonofos
Malathion
Methomyl
Carbaryl
Chlordanea
Disulfoton
Chlordanea
Dcmeton
Diazinon
Disulfoton
Endosulfan
Endrin
Carbaryl
Carbophenothion
Demeton
Diazinon
Dimethoate
Disulfoton
Ethion
Azinphos methyl
Carbaryl
Carbophenothion
Chlordanea
Diazinon
Disulfoton
EPN
Aldicarb
Carbaryl
Carbophenothion
Demeton
Diazinon
Disulfoton
Endosulfan
EPN
Fensulfothion
Azinphos methyl
Carbofuran
Diazinon
Monocrotophos
Parathion
Phorate
Toxaphene
Trichlorfon
Malathion
Methyl parathion
Parathion
Toxaphene
Heptachlor3
Malathion
Methyl parathion
Parathion
Toxaphene
Trichlorfon
Malathion
Methyl parathion
Mevinphos
Parathion
Phorate
Toxaphene
Heptachlora
Malathion
Methomyl
Methoxychlor
Methyl parathion
Parathion
Toxaphene
Trichloifon
Fonofos
Malathion
Methyl paralhion
Parathion
Phorate
Trichlorfon
Endosulfan
Endrin
Fonofos
Parathion
209
-------
Major crops and principal pesticides registered for use on them throughout the United States-Continued
Crop
Tobacco
Vegetable crops
Herbicides
Benefin Pebulate
Diphcnamid
Isopropalin
Barban Dinoseb
Bensulide Diphenamid
CDAA Endothall
CDEC EPTC
Chloramben Flurodifen
Chlorbromuron Linuron
Chloroxuron Nitralin
Chlorpropham Paraquat
Dalapon Propham
DCPA Trifluralin
Diallatc Vernolate
Insecticides and miticides
Azinphos methyl
Carbaryl
Carbofuran
Chlordanea
Diazinon
Dimcthoate
Disulfoton
Endosult'an
Ethoprop
Fensulfothion
Azinphos methyl
BHC
Carbaryl
Carbophenothion
Chlordane*
Demeton
Diazinon
Dicofol
Dimethoate
Disulfoton
Endosulfan
EPN
Ethion
L'ensulfothion
Fonofos
Heptachlor3
Fonofos
Heptachlora
Malathion
Methidathion
Methyl parathion
Monocrotophos
Parathion
Trichlorfon
Lindane
Malathion
Metaldchyde
Methomyl
Methoxychlor
Methyl parathion
Mevinphos
Naled
Parathion
Perthane
Phorate
Phosphamidon
Tetradifon
Toxaphene
Trichlorfon
a Registration status under review.
Wheat, oats, barley, millet, rye.
210
-------
APPENDIX D
CONVERSIONS AND CALCULATIONS
211
-------
APPENDIX D
CONVERSIONS AND CALCULATIONS
Multiply
Cubic feet/second
Cubic feet/second
Cubic feet
Grams/liter
Liters
Milligrams/liter
Million gals/day
Parts/million (ppm)
(Temp°C + 17.78)
(Temp°F - 32)
1 Kilogram
1 Pound
1 Gallon
1 Cubic foot/sec.
1 Cfs
By
448.831
0.646317
7.5
1000
1.057
1
1.54723
8.345
1.8
0.556
To Obtain
Gallons/minute
Million gallons/day
Gallons
Parts/million
Quarts
Parts/Million (ppm)
Cubic feet/second
Ibs/million gals.
o
Temp F
Temp C
= 2.205 pounds
= 453.6 grams
= 3.785 liters
= 646,300 gals/day
= 449 gals/min.
= 1.547 cfs
1,000,000 gals/day
1,000,000 gals/day = 694 gals/min.
1 Pound/million gals = 0.1199 ppm
Milligrams per liter x 8.34 x flow in mil. gals, day = Ibs/day
Milligrams per liter x 3.785 x flow in mil. gals./day = kg/day
REPORTING OF LABORATORY RESULTS
Parameter Report to Nearest Example
7.2 units
BODr
TSS
Report to Nearest
0.1 unit
1 mg/1
1 mg/1
34 mg/1
27 mg/1
912
-------
TECHNICAL REPORT DATA 1
(Please read Instructions on the reverse before completing)
1. REPORT NO.
4 TITLE AND SUBTITLE
Manual for Control of Pol]u1
Agriculture
Pollution Control Manual foi
2.
,
:ants Generated By Irrigated
r Irrigated Agriculture
7. AUTHOR(S)
Keith Kepler, P.E.
Don Carlson and W. T. Pitts, P.E.
9 PERFORMING ORGANIZATION NAME Af
toups Corporation
1966 West 15th Street, #1
Loveland, Colorado 80537
U' SPONSORING AGENCY NAME AND ADI
!S. Environmental Protects
1860 Lincoln Street
Denver, Colorado 80295
vID ADDRESS
3RESS i
jn Agency, Region VIII
3. RECIPIENT'S ACCESSION NO.
5. REPORT DATE 1
August 1Q7R
6. PERFORMING ORGANIZATION CODE 1
8. PERFORMING ORGANIZATION REPORT NO. 1
10. PROGRAM ELEMENT NO. I
11. CONTRACT/GRANT NO. I
68-01-3562
13. TYPE OF REPORT AND PERIOD COVERED I
Final
14. SPONSORING AGENCY CODE I
15. SUPPLEMENTARY NOTES I
manual is intended to expand understanding of irrigated agricultureTwater quality
relationships to a broad group, including water quality interests, water resource
interests, and agricultural field technicians.
Information on collecting pertinent information on the irrigation system, sampling
techniques, and evaluation techniques for determining the water quality impacts of
return flows, combined with beneficial use aspects allow irrigation to be put into
perspective with other elements of a water quality plan. Development of best
management practices (BMP's) incorporate this water quality information plus infor-
mation on the various agricultural practices. Understanding of local conditions
affecting BMP's can be developed within the evaluation framework.
Technical information on irrigated agricultural practices and the pollutants associated
with return flows is presented in a thoroughly-organized manner which makes it
available to the layman as well as to experienced personnel. Traditional and recently
developed irrigation practices are developed and evaluated in terms of use, pollu-
tant loading pathways, cost, and effectiveness. Pollutants are discussed in terms of
occurence in nature, loading mechanisms, evaluation techniques, and effect upon
beneficial use.
17. KEY WORDS AND DOCUMENT ANALYSIS |
a. DESCRIPTORS
Water Quality Water Law
Water Pollution
Agriculture
Salinity
Sediment
Nitrates
Pesticides
18. DISTRIBUTION STATEMENT
Distribution Unlimited
.IDENTIFIERS/OPEN ENDED TERMS
rrigation Systems
irrigation Management
Practices
rrigati on- Return Flow
alt Balance
Dilution Control Options
9. SECURITY CLASS (This Report)
Unclassified
20. SECURITY CLASS (This page)
c. COS ATI Field/Group I
21. NO. OF PAGES 1
223
22. PRICE 1
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
213
1?U.S, GOVERNMENT PRINTING OFFICE:1978—677-220 / 161
------- |