United States
        Environmental Protection
        Agency
Office of Water
Washington D.C.
EPA841-R-92-002
   June 1992
EPA    COMPENDIUM OF
        WATERSHED-SCALE MODELS
        FOR TMDL DEVELOPMENT

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COMPENDIUM OF WATERSHED-SCALE MODELS
                      FOR
              TMDL DEVELOPMENT
          U S Environmental Protection Agency
        Office of Wetlands, Oceans and Watersheds
            Office of Science and Technology
                   401 M St, SW
                Washington, DC 20460
                     June 1992

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                              Disclaimer

The information contained in this compendium is based on publications and
literature provided by model developers   No verification or testing of model
accuracy or function is implied by this review  The Environmental Protection
Agency does not support any model unless  support is explicitly mentioned
Mention  of  trade  names  or  commercial  products  does  not  constitute
endorsement or recommendation for use

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                              Foreword

The process for determining specific pollution reductions needed to attain State
water quality standards under the Clean Water Act is set out in Section 303(d)
of that  Act and involves the determination  of Total Maximum Daily Loads
(TMDLs)  As interpreted in EPA regulations and guidance,  the TMDL process
can be used to address large geographic areas such as river basins and provides
water quality managers with an analytical method to address more complex
water pollution problems, such as nonpomt sources,  and to adopt a more
integrated approach to water quality management   Through recent program
initiatives such  as the  Watershed  Protection Approach,  EPA  has  been
encouraging Federal, State, and local agencies concerned with water quality
management to analyze all water quality problems and stressors, and recommend
management measures on a basmwide rather than an individual source basis

This compendium, developed in  response to recommendations made at  the
Workshop on the Water Quality-based Approach for Point Source and Nonpomt
Source  Controls held  in  Chicago on June 26-28, 1991,  has identified  and
summarized the most  widely used  (as well as some  of  the  more obscure)
watershed-scale models that can facilitate the TMDL process  It is intended to
help water quality managers and other potential users decide which model best
suits their needs and available resources
Bruce Newton, Chief
Watershed Branch
Office of Wetlands, Oceans
 and Watersheds
                                         Russ Kinerson, Chief
                                         Exposure Assessment Branch
                                         Office of Science and Technology
                                                                           Si

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                               Acknowledgments

      This compendium was developed under the direction of Don Brady m EPA's
      Watershed Branch  It was prepared by Leslie L Shoemaker, Ph D, Mohammed
      Lahlou, Ph D, Sharon Thorns, Ph D , Richard Xue, Julie Wright and Marti Martin
      of Tetra Tech, Inc , Fairfax, Virginia, under EPA Contract Number 68-C9-0013,
      for the Watershed Management Section, Watershed Branch of the Assessment
      and Watershed Protection Division of the U S Environmental Protection Agency
      The authors would like to thank Donald  Brady of the Watershed Management
      Section and Bruce Newton of the Watershed Branch for their contributions to the
      preparation of this document
IV

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                              Table of Contents

                                                                         Page

1     INTRODUCTION AND PURPOSE                                            1

      1 1  Background                                                         1
      1 2  Classification of Watershed-Scale Models                                2

2     REVIEW OF SELECTED WATERSHED-SCALE MODELS                         7

      2 1 Review Methodology                                                 7
      2 2 Overview of Watershed-Scale Models                                   7
      2 3 Model Descriptions                                                   9

           231  Simple Methods                                             13
           232  Mid-Range Models                                           16
           233  Detailed Models                                             19

3     OTHER MODELS                                                        23

4     MODEL SELECTION                                                     27

      4 1  Model Characteristics                                               27
      4 2  Model Calibration and Verification                                     37

5     REFERENCES                                                          40

APPENDIX  Watershed-Scale Model - Fact Sheets                                A 1

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                                 List of Tables
Table 1     Evaluation of Model Capabilities - Simple Methods

Table 2     Evaluation of Model Capabilities - Mid-Range Models

Table 3     Evaluation of Model Capabilities - Detailed Models

Table 4     A Descriptive List of Model Components - Simple
           Methods

Table 5     A Descriptive List of Model Components - Mid-Range
           Models

Table 6     A Descriptive List of Model Components - Detailed
           Models

Table 7     Input and Output Data - Simple Methods

Table 8     Input and Output Data - Mid-Range Models

Table 9     Input and Output Data - Detailed Models

Table 10   Input Data Needs for Watershed Models

Table 11   Range of Application of Watershed Models - Simple Methods

Table 12   Range of Application of Watershed Models - Mid-Range Models

Table 13   Range of Application of Watershed Models - Detailed Models
Page

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  38
                                                                               VII

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                       1. INTRODUCTION AND PURPOSE
Simulation models are used extensively in
water quality planning and pollution control
Many types  of  models are available  to
simulate  different  environmental
phenomena and  components of  pollution
problems  For example, there are models
to  predict the  chemical  speciation  of
contaminant metals, the fate and transport
of organic compounds, the bioaccumulation
of  polar  compounds,  the  mixing   of
wastewater   plumes,  the  eutrophication
process, flow and velocity characteristics in
channels and the effects on fishery habitat,
and so on  Historically, the Environmental
Protection Agency's (EPA) water programs
and  its counterparts in State  pollution
control agencies  have focused on pollution
problems   resulting   from   wastewater
discharges Attention  is now expanding to
encompass nonpomt source problems and
storm-related problems It is also generally
recognized that  solving  these  problems
requires  a   "watershed  approach"   to
analyzing  the  problems,   engaging  the
parties that have a  stake in the  process,
and developing solutions to the  pollution
problems     Examining  problems  on  a
watershed scale is  a new challenge for
which   there are   not  well-developed
techniques and models   The purpose  of
this document is to provide the reader with
a quick compendium  of models  that are
useful for watershed-scale analysis

7.7 Background

Section 303{d) of the Clean Water  Act
(CWA) requires  States to  develop Total
Maximum Daily Loads (TMDLs) for water
quality-limited  waters where existing or
proposed  controls  do  not or  are  not
expected to result  in  attainment  and/or
maintenance of the applicable water quality
standards {WQSs}    Implementation of
section 303{d)  of the CWA has traditionally
emphasized    point   source   wasteload
allocations, which were easily enforced by
incorporating them into National  Pollution
Discharge  Elimination  System  (NPDES)
permits   as discharge limits   Nonpomt
sources were  generally not included as a
separate component of a TMDL because of
the difficulty in  measuring water quality
impacts and the effectiveness of controls
Experience   has  shown,  however,  that
controlling point source discharges does not
necessarily  ensure attainment  of WQSs,
especially when  nonpomt sources are a
significant  contributor  to  water quality
problems

It is time to consider nonpomt  sources as
distinct  from natural background pollutant
loadings and to formally address them as a
distinct  component of the TMDL equation
in  water quality  management schemes
Recognizing this fact, EPA is now stressing
more integrated water quality management
that considers  all of the sources and types
of pollution within a watershed and brings
together all  shareholders  to  develop
cooperative solutions

This new focus was clearly stated in EPA's
programmatic guidance outlining the TMDL
process (US EPA, 1991b)   By addressing
the technical  issues of  developing  and
implementing  TMDLs  within  a   broader

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Compendium of Watershed-Scale Models for TMDL Development
water quality-based management strategy,
this document sets the stage for State and
Federal agencies to establish both point and
nonpoint source  pollution  controls  on a
watershed basis

The water quality-based approach consists
of five steps, the first three of  which
constitute the TMDL process1

1)  identification  of water quality-limited
    waters that require TMDLs  and the
    pollutants causing impairment,

2)  priority   ranking   and   targeting  of
    identified waters,

3)  TMDL development,

4)  implementation of  pollution  control
    actions, and

5)  monitoring and assessment of control
    effectiveness

In complex situations  or where  nonpoint
source reductions are part of the  TMDL, a
"phased approach" may be used  Under
this  approach, available  knowledge  on
water   quality  conditions   and   BMP
effectiveness is used in conjunction with
scheduled  monitoring  and  evaluation to
develop  TMDLs that  consider point and
nonpoint sources of pollution  In fact, the
final step of the TMDL process provides for
continuous evaluation and improvement of
the TMDL and the pollution control actions
Models and data analysis techniques may
be  used in  the  implementation  of each
phase  of the TMDL process   Models can
assist in the initial evaluation, ranking and
targeting, TMDL development, evaluation of
controls, and program  tracking
As  part of  steps  1  and  2, an  initial
evaluation of water quality may be used to
focus  or  target  resources  for  TMDL
development  The use of such preliminary
screening applications can provide  water
quality managers with an initial assessment
of water quality,  pollutant loading,  and
source determination  for key watersheds
Screening   applications   are  typically
performed  with minimal  input data  and
calibration/verification    Because  of the
preliminary nature of the application and
data limitations, the accuracy of output is
often  low    The  results  of screening
applications are nevertheless adequate for
relative  comparisons  and  preliminary
decision making  As key watersheds are
identified and  additional  monitoring data
are collected, more detailed and accurate
model analyses can be initiated
 1.2 Classification of Watershed-Scale
    Models

One  challenge  faced by water  quality
managers is the lack of highly developed,
scientifically sound approaches to  identify
problems in watersheds and to predict the
results of potential control actions on water
quality  While a wide variety of models are
available,  each comes with limitations on
its   use,   applicability,   and   predictive
capabilities  The type of study will dictate
the complexity of  the development  of a
model to be selected  For example, a high-
prionty water with a number of pollutant
sources  may  require a  detailed  model
analysis    In  determining where  to set
priorities and gathering information prior to
initiating development of a TMDL, it may be
necessary to use several models or portions
of models   A wide variety of technical
tools  and techniques  are  available to

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Compendium of Watershed-Scale Models for TMDL Development
evaluate  point  and nonpomt  loads from
watersheds containing multiple sources and
land uses.  Although these tools were not
specifically designed to address the TMDL
process,  many of their capabilities can be
directly applied  to  comprehensive water
quality-based assessments.

Existing  watershed-scale  models can  be
grouped  into  three categories  - simple
methods, mid-range models,  and detailed
models -  based on the number of processes
they incorporate and the level of detail they
provide  In addition to the different classes
of models, the  level  of application  of a
given model  may vary  depending on the
objectives of the analysis

Simple Methods  The major advantage of
simple methods  is that they can provide a
rapid means of identifying  critical  areas
with minimal effort  and data requirements

Simple methods are compilations of expert
j'udgment  and   empirical   relationships
between physiographic characteristics of
the watershed and pollutant export that can
often be applied by using a spreadsheet
program  or hand-held  calculator  Simple
methods  are  often   used  when  data
limitations and budget and time constraints
preclude the use of  complex models  They
are  used  to  diagnose nonpomt source
pollution  problems  based  on  relatively
limited available information   They may be
used to  support an  assessment of the
relative significance of different sources,
guide decisions for management plans, and
focus continuing monitoring efforts

Simple methods, in general, rely on large-
scale aggregation  and  neglect  important
features  of small patches of  land  They
rely on generalized  sources of information
and  therefore   have  low  to   medium
requirements for site-specific data  Default
values provided for these  methods  are
derived from empirical relationships that are
evaluated based on regional or site-specific
data     The   estimations  are  usually
expressed as mean annual values.

Simple   methods   provide  only  rough
estimates  of  sediment  and  pollutant
loadings  and have very limited predictive
capability The  empiricism contained in the
models limits their transferabihty  to other
regions     Because  they  often  neglect
seasonal variability,  simple methods may
not be adequate to model  water quality
problems for  which  shorter   duration
loadings  are important   They  may  be
sufficient for problems such  as  nutrient
loadings  to and  eutrophication  of long-
residence-time water bodies

Mid-Range Models  The advantage of mid-
range watershed-scale models is that they
evaluate pollution sources and impacts over
broad geographic scales and therefore can
assist in  defining target areas for  pollution
mitigation programs on a watershed basis
Several mid-range models are  designed to
interface  with  geographic  information
systems   (GIS), which  greatly  facilitate
parameter estimation  Greater reliance on
site-specific data gives mid-range  models a
relatively   broad   range  of   regional
applicability     However,  the  use  of
simplifying assumptions limits the accuracy
of their predictions to within about an order
of magnitude (Dillaha,  1992) and restricts
their analysis to relative comparisons

This class of model attempts a compromise
between  the   empiricism of  the simple
methods and  the complexity of detailed
mechanistic models  Mid-range models use

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Compendium of Watershed-Scale Models for TMDL Development
a management-level approach to assessing
pollutant   sources  and  transport  in
watersheds by  incorporating  simplified
relationships   for   the   generation   and
transport of pollutants while still retaining
responsiveness to  management objectives
and  actions  appropriate  to watershed
management planning (Clark et al , 1979)
They are relatively simple and are intended
to identify problem  areas within  large
drainage basins or to make preliminary,
qualitative  evaluations of BMP alternatives
(Dillaha, 1992)

Unlike the simple methods,  which are
restricted to predictions of annual or storm
loads,  mid-range  tools  can  be used to
assess  the   seasonal   or  inter-annual
variability  of  nonpomt  source  pollutant
loadings  and  to  assess  long-term water
quality trends   Also, they can be used to
address land use  patterns and landscape
configurations in actual watersheds  They
are   based    primarily    on  empirical
relationships  and  generalized sources of
information.   In  addition, they typically
require   site-specific   data  and   some
calibration. Mid-range models are designed
to estimate the  importance of pollutant
contributions from multiple land uses and
many  individual   source   areas   in  a
watershed. Thus, they can be  used to
target  important  areas   of  pollution
generation  and identify areas best suited for
controls on a watershed basis  Moreover,
the  continuous simulation furnished  by
some of these models provides an analysis
of the relative importance of sources for a
range of storm events or  conditions  In an
effort  to  reduce  complexity  and  data
requirements,   these  models  often  are
written  for specific  applications    For
instance,   mid-range  models  can   be
designed for  application to agricultural,
urban, or mixed watersheds   Some mid-
range models simplify the description of
transport  processes  while  emphasizing
possible reductions available with controls,
others simplify the  description of control
options and  emphasize  the  changes in
pollutant concentrations  as  they  move
through the watershed

Detailed  Models.   Detailed  models best
represent  the  current  understanding of
watershed  processes  affecting pollution
generation   Detailed models are best able
to address  problem  causes  rather than
simply  describe  overall  conditions    If
properly applied  and calibrated, detailed
models can  provide  relatively accurate
predictions of  variable flows and  water
quality at any point in a watershed.  The
additional precision they provide, however,
comes at the expense of considerable time
and resource expenditure

Detailed  models  use  storm  event  or
continuous simulation to predict flow and
pollutant concentrations for a range of flow
conditions  The models are large and were
not  designed  with  emphasis  on  their
potential use by the typical State or local
planner   Many  of these models were
developed   for   research   into  the
fundamental  land surface and instream
processes influencing runoff and pollutant
generation  rather than  to  communicate
information to decision-makers faced with
planning watershed management (Biswas,
1975)

Detailed models incorporate the manner in
which watershed processes  change over
time  in a continuous fashion rather than
relying  on  simplified terms  for rates of
change (Addiscott  and Wagenet,  1985)
They tend  to require rate parameters for

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Compendium of Watershed-Scale Models for TMDL Development
flow velocities and pollutant accumulation,
settling,  and  decay instead  of capacity
terms  The length of time steps is variable
and depends on the stability of numerical
solutions as well as the response time for
the system (Nix, 1991), Algorithms in the
detailed model more closely simulate the
physical  processes of  infiltration,  runoff,
pollutant accumulation, mstream effects,
and    groundwater/surface  water inter-
actions. The input and  output of detailed
models have greater spatial and temporal
resolution  Moreover, the manner in which
physical characteristics and processes differ
over  space  is  incorporated  within  the
governing equations (Nix, 1991)  Linkage
to biological modeling is possible due to the
comprehensive  nature  of   continuous
simulation  models   In  addition, detailed
hydrologic  simulations  can  be used  to
design controls

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Compendium of  Watershed-Scale Models for TMDL Development

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            2. REVIEW OF SELECTED WATERSHED-SCALE MODELS
2.1 Review Methodology

A three-step process was used to review
existing watershed-scale models

• Model  identification    In  addition to
  information   gained  through   user
  experience,  the  model   identification
  process was  based  on  a  review of
  abstracts   obtained   from  computer
  searches, available case studies in which
  a  modeling  approach  was  used to
  address nonpomt source  pollution, and
  available published literature Receiving
  water   quality   models  and   models
  developed for field-size studies were not
  considered in this review

• Model   acquisition    The  acquisition
  process was  initiated  by  contacting
  model distributors, potential model users,
  other consultants, and model developers
  A list  of models acquired and  their
  corresponding  distributor references  is
  presented   in  the   Appendix     The
  collection of models with potential use in
  the TMDL process is ongoing

• Model documentation  Each model was
  thoroughly reviewed with respect  to its
  theoretical basis,  range of applicability,
  and  input  requirements    Additional
  references concerning model application
  were also collected and used in this step
  The results of this review were compiled
  in the  form of  fact sheets  and are
  presented  in the Appendix  This review
  forms the primary basis for the following
  discussions
2.2 Overview of Watershed-Scale Models

During  the   last  20  years,  numerous
watershed and  nonpomt source  models
have  been developed    Some of these
models  have  been (and still  are)  used
successfully   by  watershed  and  water
quality managers  Other models have had
limited   use   or   have   been   rapidly
incorporated into larger systems prior to
real world applications or testing   This
latter  group of models is not addressed in
this review In addition, watershed models
have  been  continuously  updated  and
improved in light of new developments in
computing facilities    Older versions of
currently used models are also not included
in the present compendium  Many of the
models   reviewed   were  developed  or
sponsored by  Federal or State agencies,
however,  a  few simple and  mid-range
models were developed by  universities or
private companies

The  U S  EPA  currently  supports  and
distributes two complex watershed models
the  Hydrologic  Simulation  Program  -
FORTRAN (HSPF),  for watersheds with
multiple land use categories, and the Storm
Water  Management   Model  (SWMM),
developed primarily for urban land areas
The versatility of HSPF and SWMM  for
simulating a  wide range of  land uses and
their  continual  upgrading   make  these

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Compendium of  Watershed-Scale Models for TMDL Development
models two of the most detailed and widely
applied to watershed  studies   EPA also
supports a simple screening procedure for
assessing nonpomt loads   This procedure
(McElroy et al., 1976, Amy et al , 1974,
Mills  et  al.,  1985),  a  compilation  of
empirical  relations and loading functions,
can be applied using a hand-held calculator
The  procedure provides  average annual
estimates of loadings of toxic compounds
in  addition  to  those  of  conventional
pollutants.

The U S. Department of Agriculture - Soil
Conservation  Service  (USDA-SCS)  has
developed several relatively simple,  well-
documented models that may potentially be
considered for TMDL development in rural
and   agricultural   watersheds  (e  g ,
Agricultural  Non-Point Source  Pollution
Model (AGNPS);  Simulator  for Water
Resources  in  Rural Basin-Water Quality
model (SWRRB  or SWRRBQ),  Erosion-
Productivity  Impact  Calculator  (EPIC),
Groundwater Loading Effects of Agricultural
Management   Systems   (GLEAMS),
Chemicals,   Runoff,   Erosion   from
Agricultural  Management   Systems
(CREAMS);  and  Nitrate  Leaching and
Economic   Analysis  Package  (NLEAP))
These models were designed for various
purposes   ranging   from   the  simple
estimation  of  runoff and sediment loads
from  individual  storm events  to  runoff
routing,  point  and   nonpomt  source
contributions,  and  continuous runoff and
subsurface  flow modeling  on  complex
watersheds.  Field-scale models, such as
GLEAMS, CREAMS, NLEAP, and EPIC are
designed   for   specific  agricultural
applications and may be  used to target
specific pollution sources,  land  uses,  or
land activities and to test the efficiency of
control practices. The SWRRB model can
be  applied  on a  watershed  basis  for
continuous  simulation,   but  additional
development   and  testing   of  model
components for nutrient  and  pesticide
transport is under way  The AGNPS model
is watershed-scale but is currently limited in
application to design storms  The USDA is
upgrading AGNPS  to  include continuous
simulation

The   U S  Army  Corps  of  Engineers
Hydraulic  Engineering   Center   (HEC)
developed a continuous urban simulation,
including dry-weather sewer flows, in their
Storage,  Treatment,  Overflow,  Runoff
Model (STORM)   With support of HEC,
STORM  has  been  used  extensively  for
planning  purposes and  for  evaluating
control  strategies  for combined  sewer
overflows   The U S  Geological  Survey
(USGS) has developed and applied  the
Distributed Routing Rainfall Runoff Model
(DR3M-QUAL),  calculating  runoff   and
pollutant loads in several urban watersheds
The   USGS  also  developed  a  simple
statistical method based on monitoring data
from  several  gaging stations  The U S
Federal Highway Administration developed
and used a simple  pollutant loading model
(FHWA)  to assess water  quality  due to
stormwater runoff  from highways and to
develop   preliminary  pollution   control
options

A number of models  were developed at
universities or other research institutions
The   Areal* Nonpomt  Source Watershed
Environment Response Simulation model
(ANSWERS)  was  developed   at   the
University  of  Georgia  to  predict  the
movement of sediment through relatively
large  agricultural watersheds  The Source
Loading and Management Model (SLAMM)
was  developed  at   the  University  of
8

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Compendium of Watershed-Scale Models for TMDL Development
Alabama for the purpose  of evaluating
urban management practices for sediment,
nutrients,   and  other   urban pollutants
including toxics  and oxygen-demanding
substances   The Generalized Watershed
Loading Function (GWLF) model, a mid-
range model,  was  developed at Cornell
University  The GWLF  model  considers
runoff from rural and urban land uses and
integrates pollution from both point sources
and  nonpomt  sources    Watershed is a
simple nonpomt source model developed at
the University of Wisconsin to assess the
cost-effectiveness of stormwater control
practices

Several  State  and  local agencies  have
participated in the development of nonpomt
source models  Water Screen  is a loadmg-
function-based  method developed by the
Office of  Planning  and  Zoning,  Anne
Arundel County, Annapolis, Maryland The
Illinois State  Water  Survey developed a
mid-range model (Auto-Q-llludas  or Auto-
Ql) for continuous simulation  of  pollutant
loading   from   built-up  areas     The
Washington   Metropolitan   Council   of
Governments   developed  a   simplified
approach,  "the  Simple  Method,"   for
estimating pollutant  loads from urban land
uses  (Schueler, 1987)   This  approach
relies on data  from the National  Urban
Runoff Program (NURP) for default values
Watershed  Management Model (WMM) is
under   development  for  the   Florida
Department of Environmental Regulation to
evaluate nonpomt source pollution loads
and   control   strategies     The  Urban
Catchment  Model   (P8-UCM),   was
developed for the Narragansett Bay Project
The  P8-UCM   model predicts  pollutant
loading and transport of storm water runoff
from urban  watersheds
Other   models  developed   by  private
companies include the Simplified  Particle
Transport  Model   (SIMPTM)  and  the
Nonpomt  Source Model for  Analysis and
Planning  (NPSMAP)    SIMPTM     was
developed  by  OTAK,  Incorporated, to
estimate pollutant  loads from impervious
areas and to evaluate the effectiveness of
a number of urban stormwater practices
The NPSMAP is a spreadsheet-based model
designed to simulate stream segment load
capacities  (LCs), point source wasteload
allocations (WLAs), and nonpomt source
load allocations (LAs)

2.3 Model Descriptions

Several watershed-scale models have been
selected as potential candidates for use in
the TMDL development process and are
included in this compendium  A qualitative
evaluation  of each model  in terms of its
simulation   capabilities,   modeling
performance,  and   ease  of  use   was
developed  from  available  documentation
and  published applications to real-world
case studies The results of this qualitative
evaluation  for  the  three categories of
models are summarized in Tables 1, 2, and
3  These models differ in the type  and the
manner  in  which  they   describe  the
hydrologic and pollutant loss processes, the
type of pollutant and pollution sources they
address, the level of accuracy they provide,
and the input data, personnel training, and
resources and computing capabilities they
require

Simple methods generally use simplistic and
empirical  relations  to describe a  limited
number  of  hydrologic   and  pollution
processes  As can be seen from Table 1,
these methods  use large simulation time
steps to provide  long-term  averages or

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Table 1  Evaluation of Model Capabilities - Simple Models
Criteria
Land Uses
Time Scale
Hydrology
Pollutant
Loading
Pollutant
Routing
Model Output
Input Data
BMPs
Documentation
Urban
Rural
Point Sources
Annual
Single Event
Continuous
Runoff
Baseflow
Sediment
Nutrients
Others
Transport
Transformation
Statistics
Graphics
Format Options
Requirements
Calibration
Default Data
User Interface
Evaluation
Design Criteria

EPA1
Screening
O
G
_
•
o
-
_4
-
O
e
G
_
-
-
-
-
O
-
•
-
o
-
•
Simple1
Method
G
-
-
•
O
-
G
-
€
G
€
-
-
-
-
-
O
-
•
-
O
-
•
Regression
Method
G
O
-
•
0
-
-
-
G
G
€
-
-
-
-
-
O
-
G
-
-
-
•
SLOSS-,
PHOSPH
-
G
-
•
-
-
-
-
O
0
-
-
-
-
-
-
O
0
G
-
o
-
«
Water
Screen
O
o
-

-
-
-
-
0
G
-
-
-
-
-
-
o
0
o
o
o
-
G
Watershed
C
o
o
•
-
-
-
-
G
€
0
-
-
€
€
O
O
€
O
«
4
-
•
FHWA
O3
0
-
•
0
-
o
-
-
0
€
-
-
O
-
-
o
-
€
O
€
-
•
WMM
•
•
O
•
-
-
o
o
_
€
€
-
O
0
0
o
o
€
€
O
O
-
O
Not a computer program 4 Extended versions recommend use of • High C Medium O Low - Not Available
Coupled with GIS SCS-curve number method
3 Highway drainage basins for runoff estimation
                                                                                 I
                                                                                 I
                                                                                 s?
                                                                                 !
                                                                                 1
                                                                                I
                                                                                 i

-------
Table 2  Evaluation of Model Capabilities - Mid-Range Models
Criteria
Land Uses
Time Scale
Hydrology
Pollutant
Loading
Pollutant
Roubng
Model Output
Input Data
BMPs
Documentation
Urban
Rural
Point Sources
Annual
Single Event
Continuous
Runoff
Baseflow
Sediment
Nutrients
Others
Transport
Transformation
Statistics
Graphics
Format Options
Requirements
Calibration
Default Data
User Interface
Evaluation
Design Criteria

NPSMAP
•
•
€
-
0
•
9
o
-
•
-
o
-
€
G
•
€
O
•
9
O
-
•
GWLF
•
•
G
-
-
•
•
•
•
•
-
O
-
O
G
•
G
O
•
•
O
-
O
P8-UCM
•
-
•
-
•
-
•
_
-
•
•
0
-
-
•
•
G
O
G
•
•
•
*
SIMPTM
•
-
_
-
_
-
•
O
•
•
•
o
-
o
-
•
G
o
o
4)
G
O
O
Aiito-QI
•
-
-
-
-
•
•
O
•
•
•
G
-
-
-
O
O
G
O
G
G
C
G
AGNPS
-
•
•
-
•
-
•
-
•
•
-
•
-
-
•
•
c
0
o
€
€
O
•
SLAMM
•
-
•
*•
-
•
•
0
•
•
•
€
-
O
O
•
o
o
€
•
O
o
€
I
I
                                                                                        or

                                                                                        I
                                                                                        I
                                                                                        I

                                                                                       I
                                                                                       i
                                         • High  C Medium  O Low    - Not Available

-------
Table 3  Evaluation of Model Capabilities - Detailed Models
Criteria
Land Uses
Time Scale
Hydrology
Pollutant
Loading
Pollutant
Routing
Model Output
Input Data
BMPs
Documentation
Urban
Rural
Point Sources
Annual
Single Event
Continuous
Runoff
Baseflow
Sediment
Nutrients
Others
Transport
Transformation
Statistics
Graphics
Format Options
Requirements
Calibration
Default Data
User Interface
Evaluaton
Design Criteria

STORM
•
-
•
-
O
•
•
o
•
•
•
_
-
o
-
•
€
O
€
_
€
€
•
ANSWERS
-
•
-
-
•
-
•
-
•
•
-
€
-
-
•
•
•
O
O
_
€
€
O
DR3M
•
-
•
-
O
•
•
o
•
•
-
•
-
•
C
•
•
Q
•
O
•
€
O
SWRRBWQ
O
•
•
-
0
•
•
•
•
•
•
•
-
•
c
•
o
o
•
o
€
-
•
SWMM
•
0
•
-
•
•
0
•
•
•
•
o
o
•
0
•
•
•
0
-
•
•
•
HSPF
•
€
•
-









•
O
•
•
•
€
-
•
•
•
                                  f
                                                                                      9-
                                                                                      i
                                                                                      I

                                                                                     f
                              High     Q Medium
O Low
- Not Available

-------
Compendium of Watershed-Scale Models for TMDL Development
annual estimates  However, although they
can easily be adopted to estimate seasonal
or storm event  loadings, their  accuracy
decreases since  they  cannot capture the
large  fluctuations of pollutant loading or
concentration usually observed at smaller
time steps  In general, these methods rely
on  available  default values and do  not
implicitly   relate   pollutant   loads   to
hydrological processes  Pollutant loads are
determined from export coefficients (e g ,
Watershed)  or  as  a function  of  the
sediment  yield   (e g ,  EPA  screening
procedures,   SLOSS-PHOSPH,  Water
Screen)  The Simple Method, regression
method,  and    FHWA   methods   are
statistically based approaches developed
from  past monitoring information   Their
application is limited to the areas for which
they were  developed and to watersheds
with similar land uses or activities

Mid-range models attempt to use smaller
time steps  in order to  represent seasonal
variability, therefore they require additional
meteorologic data (e g , daily weather data
for the GWLF, hourly rainfall for NPSMAP)
They  also  attempt to  relate  pollutant
loadings to hydrologic (e g , runoff)  and
erosion  (e g , sediment yield) processes
These models  usually include  adequate
input-outputfeatures (e g ,AGNPS, GWLF),
making  applications  easier to  process
Several  of these models (NPSMAP, Auto-
Ql)  were developed in existing computing
environments (e  g ,  Lotus 1-2-3®) to make
use of their built-in graphical and statistical
capabilities It should be noted from Tables
1 and 2 that neither the simple nor the mid-
range models consider degradation  and
transformation    processes,   and   few
incorporate  adequate  representation  of
pollutant transport  within and  from  the
watershed    Although their  applications
may be limited  to  relative  comparisons,
however, they may provide  water quality
managers  with  necessary information for
watershed-plannmg-level decisions

More detailed models, on the other hand,
attempt to simulate the physical processes
governing   hydrologic   and   pollutant
transport and transformation mechanisms
Table 3 shows that these models use small
time steps to allow for continuous and
storm event simulations   However, input
data file preparation and calibration require
professional   training   and    adequate
resources   Some of these  models (e g ,
STORM,   SWMM,   ANSWERS)   were
developed  not only to support  planning-
level evaluations but also to provide design
criteria for pollution control  practices  If
appropriately   applied,   state-of-the-art
models such as HSPF and SWMM can
provide accurate estimations of pollutant
loads   and  expected  impacts  on  water
quality   However,  their added  accuracy
may not always justify the amount of effort
and resources they require  Application of
such detailed models is more cost-effective
when used to address complex situations or
objectives

A qualitative description of each model is
presented  in  the   following  section  to
supplement the information reported  in
Tables 1, 2, and 3   For a more technical
description, the  reader is  referred to the
Appendix to this compendium

2.3.1   Simple Methods

EPA Screening  Procedures    The  EPA
Screening Procedures were  developed by
the EPA Environmental Research Laboratory
in Athens, Georgia, (McElroy et al ,  1976,
Mills,   1985)  to  calculate pollutant loads
                                                                                 13

-------
Compendium of Watershed-Scale Models for TMDL Development
from point and nonpomt sources, including
atmospheric  deposition,  for  preliminary
assessment  of  water  quality     The
procedures consist of loading functions and
simple  empirical   expressions   relating
nonpomt pollutant loads  to other readily
available  parameters     Data   required
generally  include  information  on  land
use/land cover, management  practices,
soils, and  topography   Although  these
procedures are  not coded into a computer
program, several  computer-based models
have adapted the loading function concept
to predict pollutant loadings   An advantage
of this approach is the possibility of using
readily  available data as default values
when site-specific information is lacking
Application of  these  procedures requires
minimum personnel training and practically
no  calibration.   However,  application  to
large,  complex watersheds  should  be
limited to pre-planning activities

The Simple Method. The Simple Method is
an  empirical   approach   developed  for
estimating  pollutant  export from  urban
development sites in the  Washington, DC
area (Schueler, 1987)  It is used at the
site-planning  level  to  predict  pollutant
loadings under a  variety of development
scenarios.  Its application is limited to small
drainage areas of less than a square mile
Pollutant concentrations  of phosphorus,
nitrogen,   chemical   oxygen   demand,
biological   oxygen  demand (BOD), and
metals are  calculated from  flow-weighted
concentration  values for  new  suburban
areas, older urban areas, central business
districts, hardwood  forests, and   urban
highways.  The method relies on the NURP
data for default values (US EPA, 1983)  A
graphical relationship is used to determine
the event  mean  sediment  concentration
based on readily available information This
method is  not  coded  into a  computer
program  but  can be  easily implemented
with a hand-held calculator

USGS   Regression    Approach      The
regression approach developed  by USGS
researchers  is   based  on  a  statistical
description  of historic records  of storm
runoff responses on  a watershed level
(Tasker and Driver,  1988)   This  method
may  be  used   for  rough  preliminary
calculations of annual pollutant loads when
data  and  time  are  limiting     Simple
regression equations were developed using
available  monitoring  data  of  pollutant
discharges at over 70 gaging stations in 20
States  Separate equations are given for
ten pollutants, including dissolved and total
nutrients, chemical  oxygen demand, and
metals  Input data include drainage area,
percent  imperviousness,   mean   annual
rainfall, general land use pattern, and mean
minimum monthly temperature Application
of  this  method  provides  storm-mean
pollutant   loads   and   corresponding
confidence  intervals    The use  of this
method as a planning  tool  at a regional or
watershed  level may require preliminary
calibration and verification  with additional,
more recent monitoring data

Simplified   Pollutant   Yield   Approach
(SLOSS-PHOSPH)  This method uses two
simplified loading algorithms to evaluate
soil erosion, sedimentation, and phosphorus
transport from distributed watershed areas
The SLOSS algorithm provides estimates of
sediment   yield,  while  the  PHOSPH
algorithm  uses  a  loading function  to
evaluate  the amount of sediment-bound
phosphorus  Application to watershed and
subwatershed levels was developed by Tim
et  al  (1991)  based  on  an  integrated
approach coupling these algorithms with
14

-------
Compendium of  Watershed-Scale Models for TMDL Development
the  Virginia  Geographical  Information
System  (VirGIS)     The  approach  was
applied to the Nommi  Creek Watershed,
Westmoreland County, Virginia, to target
critical areas of nonpomt source pollution at
the subwatershed level  In this application,
analysis was limited to phosphorus loading,
however, other pollutants for which input
data or default values are available can be
modeled  in a similar fashion The approach
requires full-scale GIS capability and trained
personnel

Water  Screen     Water  Screen   was
developed by the Office of Planning and
Zoning, Anne Arundel County, Annapolis,
Maryland, for the Apple II  microcomputer
The  program can be used at the planning
level to  estimate  loadings of sediment,
nitrogen, phosphorus, BOD, lead, and zinc
from various land uses in a  watershed
This  model  uses   a   loading  function
approach similar to that developed in the
EPA screening procedures (McElroy et al ,
1976)  and does not require meteorologic
data since pollutant loads are computed
from   estimates   of   sediment   yield
Estimation of nitrogen loads considers both
losses  from surface  soils  and input  from
precipitation. This model was tested on the
Church  Creek   watershed,   south   of
Annapolis, Maryland (Bird and Conaway,
1985)

Watershed.   Watershed is a  spreadsheet
model  developed  at  the  University  of
Wisconsin to calculate phosphorus loading
from   point  sources,   combined  sewer
overflows  (CSOs),  septic  tanks,   rural
croplands,  and   other  urban and   rural
sources  The Watershed program can  be
used to  evaluate the  tradeoffs  between
control  of  point and  nonpomt sources
(Walker,  Pickard, and Sonzogni, 1989)   It
uses an annual time step to calculate total
pollution loads and  to evaluate the cost-
effectiveness of pollution control practices
in term of cost per unit load reduction  The
program uses a  series of worksheets to
summarize watershed characteristics and to
estimate pollutant loadings for uncontrolled
and controlled conditions   Because of the
simple formulation describing the various
pollutant loading  processes, the model can
be applied  using available  default values
with  minimum   calibration   effort
Watershed   was  applied  to  study  the
tradeoffs between  controlling point  and
nonpomt sources  in the  Delavan Lake
watershed in Wisconsin

The   Federal  Highway    Administration
(FHWA) Model   The Office of Engineering
and  Highway Operations  has developed  a
simple statistical  spreadsheet procedure to
estimate pollutant loading and impacts to
streams  and lakes  that receive  highway
stormwater   runoff  {Federal   Highway
Administration, 1990) The procedure uses
several  worksheets  to   tabulate  site
characteristics and other input parameters,
as well as  to calculate  runoff volumes,
pollutant loads,  and the  magnitude  and
frequency  of  occurrence  of  instream
pollutant concentrations  The FHWA model
uses a set of default values for  pollutant
event-mean concentrations that depend on
traffic volume and the rural or urban setting
of the highway's pathway  This method is
used   by   the   Federal  Highway
Administration to identify and quantify the
constituents  of highway  runoff and their
potential effects on receiving waters and to
identify areas that may require controls

Watershed Management  Model (WMM)
The  Watershed  Management Model  was
developed for the Florida  Department of
                                                                                 15

-------
Compendium of Watershed-Scale Models for TMDL Development
Environmental Regulation for watershed
management planning  and estimation  of
watershed pollutant loads (Camp, Dresser,
and McKee, 1992).  Pollutants simulated
include nitrogen, phosphorus, lead, and zinc
from  point  and  nonpomt sources   The
model is implemented in the Lotus 1-2-3®
spreadsheet environment and  will  thus
calculate standard statistics and produce
plots and bar charts of  results Although it
was developed to predict annual loadings,
this  model  can  be adapted  to  predict
seasonal loads provided that seasonal event
mean concentration data are available  In
the absence of site-specific information, the
event concentration derived from the NURP
surveys may be used as default values The
model includes computational components
for stream and lake water quality analysis
using simple transport  and transformation
formulations  based on travel  time  The
WMM  has   been   applied  to   several
watersheds including the development of a
master plan for Jacksonville, Florida, and
the Part II estimation of watershed loadings
for the NPDES permitting  process   It has
also  been  applied  in Norfolk County,
Virginia; to a Watershed Management Plan
for North Carolina, and  to a  wasteload
allocation study for Lake Tohopekaliga, near
Orlando, Florida.
2.3.2 Mid-Range Models

Nonpoint  Pollution  Source   Model  for
Analysis  and   Planning  (NPSMAP).
NPSMAP is spreadsheet program developed
to simulate  nonpomt source  runoff and
nutrient  loadings,  in  addition  to  point
source  discharges  (Omicron  Associates,
1990). Nonpoint source runoff simulations
incorporate  irrigation, evapotranspiration,
and drainage to groundwater  Point source
discharge simulations include  infiltration,
overflows and bypasses, and  changes in
treatment plant performance  NPSMAP can
also  evaluate surface water  storage  in
reservoirs and wetlands,  evaluate water
uses, and perform preliminary water quality
analyses  The  model can  be  used  to
evaluate user-specified alternative control
strategies, and it simulates stream segment
load  capacities  (LCs)  in  an  attempt  to
develop point source wasteload allocations
(WLAs)  and   nonpomt   source   load
allocations  (LAs)  Probability distributions
for  runoff  and nutrient loadings can  be
calculated by the model based on either
smgle-eventor continuous simulations  The
model can be applied in urban,  agriculture,
or complex watershed simulations   The
spreadsheet-based   NPSMAP    operates
within   the   Lotus  1-2-3®  programming
environment  and  is capable of producing
graphic  output   Although  this  model
requires  a  minimum calibration  effort, it
requires  moderate effort to prepare input
data files    The current  version of  the
program considers  only nutrient  loading,
sediment and other pollutants  are not yet
incorporated into the program The model is
easily interfaced with CIS (ARC/INFO) to
facilitate preparation of land use files  The
developers also plan to interface the model
with remote sensing facilities for updated
land  use information  NPSMAP has been
applied to the Tualatin River basin for the
Oregon  Department   of  Environmental
Quality
Generalized Watershed Loading Functions
(GWLF) Model   The  GWLF model  was
developed at Cornell University to assess
the point and nonpomt loadings of nitrogen
and  phosphorus from  a relatively large,
agricultural and  urban  watershed and  to
16

-------
Compendium of Watershed-Scale Models for TMDL Development
evaluate the effectiveness of certain land
use  management  practices  (Harm  and
Shoemaker, 1987)  One advantage of this
model  is  that  it was written with the
express purpose of requiring no calibration,
making   extensive   use  of   default
parameters.   The GWLF  model includes
rainfall/runoff and  erosion and sediment
generation components, as  well as  total
and  dissolved  nitrogen and phosphorus
loadings  The current version of this model
does not account for loadings of toxics and
metals, but with  minimal  effort improve-
ments  can be made to add this feature
This model uses daily time steps and allows
analysis of annual and seasonal time series
The  model  also  uses  simple transport
routing,  based  on   the  delivery  ratio
concept In addition, simulation results can
be  used   to  identify  and rank  pollution
sources   and   evaluate    basmwide
management   programs   and   land  use
changes  The model also includes several
reporting and graphical representations of
simulation output to aid in interpretation of
the results  This model was successfully
tested  on a medium-size watershed in New
York (Haith and Shoemaker, 1987)   It is
currently  being updated  to  include  an
enhanced  user  interface  with  potential
Jinking to  available national databases for
rapid   and   effective   assessment   of
watershed point and  nonpomt  source
pollution problems

Urban  Catchment Model (P8-UCM)  The
P8-UCM  program was developed for the
Narragansett  Bay Project  to simulate the
generation and transport of stormwater
runoff  pollutants in small urban catchments
and to assess impacts of development  on
water  quality, with  minimum site-specific
data   It includes  several  routines for
evaluating the expected removal efficiency
for particular site plans, selecting or siting
best   management   practices   (BMPs)
necessary to achieve a specified pollutant
removal,  and  comparing  the   relative
changes in pollutant loads as a watershed
develops (Palmstrom and  Walker, 1990)
Default input parameters  can  be  derived
from NURP data  and are available as a
function of land use, land cover, and soil
properties   However, without  calibration,
the use of model results should be limited
to relative comparisons   Spreadsheet-like
menus  and on-line  help documentation
make  extensive user interface possible
On-screen  graphical  representations  of
output  are  developed   for  a   better
interpretation of simulation  results   The
model   also  includes  components  for
performing  monthly   or   cumulative
frequency  distributions  for flows  and
pollutant loadings

Simplified   Particle   Transport   Model
(SIMPTM)      The   Simplified   Particle
Transport Model was developed by OTAK,
Inc  to simulate  runoff,  sediment, and
pollutant yield from urban watersheds and
to determine the effectiveness of controls
such   as  street  sweeping  (Sutherland,
Green, and Jelen,  1990)  Runoff volumes,
durations,  pollutant  loadings,  and  event
mean concentrations are reported for each
rainfall  event  on a watershed  and  a
subcatchment basis  Included in the model
results are standard statistics for  average
monthly and annual loadings  SIMPTM is
an event- or multiple-event-based model for
simulation   of  urban   nonpomt   source
loadings  for   six  pollutants,  including
sediment, metals, nutrients,  and chemical
oxygen demand The model simulates the
accumulation,  washoff,  and  mechanical
removal  of   pollutants  contained   in
particulate matter that builds up on streets
                                                                                 77

-------
Compendium of Watershed-Scale Models for TMDL Development
SIMPTM  was  calibrated using the NURP
data from  Lake Hills basin in Bellevue,
Washington    NURP data from  nearby
Surrey Downs  basin were used for testing
SIMPTM  The observed variability of runoff
was greater than  was  predicted  by the
model,  but the  estimates were  good
considering the simplistic approach used for
generating runoff  SIMPTM was used for
planning  stormwater management for the
area surrounding Reno, Nevada

Automated Q-ILLUDAS (AUTO-QI)  AUTO-
QI is a watershed model developed by the
Illinois State  Water  Survey  to perform
continuous  simulations  of  stormwater
runoff from pervious and impervious urban
lands (Terstnep et al , 1990)  It also allows
the examination of storm events or storm
sequence impacts  on  receiving   water
Critical events are  also identified by the
model   However,  hourly weather input
data  are required    Several  pollutants,
including   nutrients,  chemical   oxygen
demand,  metals,  and  bacteria can be
analyzed simultaneously  This  model also
includes  a  component  to evaluate the
relative effectiveness of best management
practices    An updated  version  of Q-
ILLUDAS, with an improved user interface
and linkage to the Geographic Information
System (ARC/INFO on PRIME  computer),
has  been completed by the Illinois State
Water Survey  This interface is provided to
generate the necessary input files relating
to land use, soils, and control measures
AUTO-QI was recently  verified  on the
Boneyard Creek in Champaign, Illinois  The
model was also applied to the Greater Lake
Calumet  area to determine annual pollutant
loadings  to the Calumet and Little  Rivers,
south of Chicago
Agricultural  Nonpomt  Source  Pollution
Model (AGNPS)  Developed by the USDA
Agricultural  Research  Service,   AGNPS
addresses concerns related to the potential
impacts  of  point  and  nonpomt  source
pollution on surface  and  groundwater
quality  (Young  et al ,  1989)    It was
designed   to   quantitatively  estimate
pollution loads from agricultural watersheds
and  to  assess  the  relative effects  of
alternative  management  programs  The
model simulates surface water runoff along
with nutrient and  sediment constituents
associated   with  agricultural  nonpomt
sources, and   point  sources  such  as
feedlots, wastewater treatment plants, and
stream bank or gully erosion  The available
version of AGNPS is storm-event based,
however, the USDA will soon be releasing
a   continuous  simulation   version,
ANNAGNPS  The structure  of the model
consists of  a square grid cell system to
represent  the   spatial  distribution  of
watershed  properties  This  grid  system
allows the model to be connected to other
software such as Geographical Information
System (GIS) and Digital Elevation Models
(DEM)   This connectivity can facilitate the
development of a number of the  model's
input  parameters    Two   new  terrain-
enhanced versions of the model, AGNPS-C,
a contour-based version, and AGNPS-G, a
grid-based version, have been developed to
automatically generate the  grid  network
and  the required topographic parameters
(Panuska et al , 1991)   The model also
includes enhanced  graphical  represen-
tations  of input and output information
AGNPS  has been  extensively used  by
resource  agencies   in   Minnesota  and
surrounding States  It was also applied to
develop  cost-effective  nonpomt  pollution
control alternatives in Idaho and Illinois and
St  Albans Bay, Vermont  GIS was linked
18

-------
Compendium of  Watershed-Scale Models for TMDL Development
with AGNPS to model sediment loading to
surface  waters of the Wet Beaver Creek
watershed of North-Central Arizona

Source  Loading and Management Model
(SLAMM)   SLAMM was developed at the
University  of   Alabama  to  assist  in
evaluating the effects of alternative control
practices and development characteristics
on urban runoff quality and quantity (Pitt,
1986)   It evaluates only runoff charac-
teristics  at  the source  areas  in   the
watershed and the discharge outfall, it does
not  directly  evaluate  receiving  water
responses  However, output data from the
model have been used in conjunction  with
other receiving water models to examine
the ultimate effects of urban runoff  The
model  performs continuous storm mass
balances for both particulate and dissolved
pollutant loadings,  and computes runoff
flow volume for different development and
ram  characteristics   It is  intended to be
used as a plannmg-level tool and to provide
rapid assessment   of  the  effects  of a
number  of  urban  stormwater  control
practices   including  detention   basins,
infiltration devices, porous pavement, street
cleaning,  grass swales, and roof runoff
disconnections  Proposed  features to be
added in an upcoming version of the model
include  cost   estimates  of  stormwater
control practices, graphical summaries, and
baseflow   and   snowmelt   predictions
SLAMM was used in Wisconsin to evaluate
the  trade-offs  between increased street
sweeping,  diversion  of  roof  drains  to
pervious areas, and detention basins, as
well as combinations of these practices
The  costs per unit of suspended solids
removal was compared in order to rank the
control  options  The model has also  been
used to evaluate pathogens from CSOs, for
Madison,  Wisconsin's stormwater permit
program, and in Birmingham, Alabama and
in Ottawa and Toronto, Canada

Sewer Overflow Model (SOM)  SOM was
developed by Limnotech as a hybridized
version of the  urban STORM and SWMM
models   It  generates pollutant  loadings
from  urban  land  uses  and evaluates
transport through interconnected sewer line
networks   SOM  has been applied in  six
locations to  study CSOs and stormwater
pollution  A  15-year continuous simulation
was performed  for Portland, Oregon, and
options  for  controlling dissolved oxygen
(DO) problems associated with large storm
events   in  Richmond,   Virginia   were
analyzed   It also has  been applied  for
evaluation of  CSOs  in  Wayne  County,
Michigan, and South Bend, Indiana   SOM
can perform simulations of an event or a
continuous series of events  It is used to
evaluate  existing  conditions as well  as to
perform plannmg-level analysis of controls

2.3.3 Detailed Models

Storage, Treatment, Overflow Runoff Model
(STORM). STORM is a U S  Army Corps of
Engineers (COE)  model  developed  for
continuous simulation of  runoff  quantity
and quality, including sediments and several
conservative pollutants   It also simulates
combined  sewer  systems  (Hydrologic
Engineering  Center, 1977)  STORM has
been  widely   used  for   planning  and
evaluation   of   the   trade-off   between
treatment and  storage control options for
CSOs    Long-term  simulations of  runoff
quantity and quality lend themselves to the
construction   of   duration-frequency
diagrams   These diagrams are  useful  in
developing urban  planning alternatives and
designing structural  control  practices
STORM  was   primarily   designed   for
                                                                                 19

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Compendium of  Watershed-Scale Models for TMDL Development
modeling stormwater runoff  from urban
areas.   It requires relatively moderate to
high calibration and  input data   STORM
was initially  developed   for  mainframe
computer usage; however, several versions
have been  adapted by various  individual
consultants for use on microcomputers

Areal   Nonpoint   Source   Watershed
Environment Response Simulation  Model
(ANSWERS).      ANSWERS   is   a
comprehensive model  developed at the
University  of  Georgia to evaluate the
effects of land  use, management schemes,
and conservation practices or structures on
the quantity and quality of water from both
agricultural and nonagncultural watersheds
(Beasley, 1986)  The distributed structure
of this model allows for a better analysis of
the spatial as well as temporal  variability of
pollution sources and loads  It was initially
developed  on   a  storm  event  basis  to
enhance the physical  description of erosion
and sediment  transport processes   Data
file preparation for the ANSWERS program
is rather complex and requires mainframe
capabilities,  especially when  dealing with
large watersheds  The output routines are
quite flexible;  results may be obtained in
several tabular and graphical  forms   The
program has   been  used  to   evaluate
management  practices  for  agricultural
watersheds  and   construction   sites   in
Indiana.   It  has  been  combined  with
extensive monitoring programs to evaluate
the  relative   importance  of  point  and
nonpomt source contributions to Saginaw
Bay.     This  application  involved  the
computation of unit area loadings under
different land use scenarios for evaluation
of the trade-offs between LAs and WLAs
Recent   model   revisions   include
improvments to the nutrient transport and
transformation subroutines (Dillaha et al ,
1988)   Future improvements may include
linkage of the grid-based system with CIS
technology

Distributed Routing Rainfall Runoff Model
(DR3M  or  DR3M-QUAL)    The  DR3M
model,  including  a  quality  simulation
component, is  supported  by  the U S
Geologic  Survey  (USGS)  (Alley,   1986)
This model was developed for the study of
conventional pollutants  m  predominantly
urban watersheds and includes components
for sewer flow routing   It can  be  used at
the planning assessment level  and as  a
design tool  It is both a continuous and
storm event-based simulator of nutrient and
sediment  loadings   The  model requires
moderate to high calibration combined with
a high level of personnel training   It also
requires mainframe computing capabilities
Adequate   input/output   features  are
incorporated into the model to facilitate use
and result  interpretations  Time  series
hydrographs and  pollutographs can  be
presented in tabular or graphical form  The
USGS has used DR3M-QUAL for calculating
urban  runoff pollutographs in  Southern
Florida, Anchorage, and Fresno (Donigian
and Huber, 1991)

Simulation for Water Resources m Rural
Basins  -  Water  Quality  (SWRRB  or
SWRRBQ)    The  SWRRBQ model was
adapted  from  the  field-scale  CREAMS
model  by USDA  to  simulate hydrologic,
sedimentation,  nutrient,  and  pesticide
movement  in    large,   complex  rural
watersheds  (Arnold  et  al ,    1989)
SWRRBQ uses a daily time step to evaluate
the effect of  management decisions  on
water,  sediment  yields,   and  pollutant
loadings  The processes simulated within
this  model  include   surface   runoff,
percolation,  irrigation   return   flow,
20

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Compendium of Watershed-Scale Models for TMDL Development
evapotranspiration,  transmission  losses,
pond and reservoir storage, sedimentation,
and  crop growth   The model is useful for
estimation  of the order of magnitude of
pollutant  loadings  from  relatively small
watersheds  or   watersheds  with fairly
uniform properties  Input requirements are
relatively high, and experienced personnel
are  required for successful simulations
The  National Oceanic  and Atmospheric
Administration (NOAA) is using SWRRBQ to
evaluate  pollutant  loadings  to   coastal
estuaries and embayments  as part of its
national   Coastal   Pollution   Discharge
Inventory  The model has been run for all
major estuaries  on the east coast, west
coast, and gulf coast for a  wide range of
pollutants (Donigian and Huber, 1991)

Storm Water Management Model (SWMM)
SWMM is a comprehensive watershed-scale
model  developed  by  EPA  (Huber  and
Dickinson, 1988)  It was initially developed
to address  urban  stormwater and assist in
storm-event  analysis  and  derivation of
design criteria for structural  control of
urban stormwater  pollution   Recently,
SWMM was upgraded to allow continuous
simulation  and   application to  complex
watersheds and land uses   SWMM can be
used to model several types of pollutants
provided that input data are available  No
user-enhanced   interface   is   currently
provided to  assist in input data  entry
However a windows-based user interface is
under development  Recent versions of the
model can be used for either continuous or
storm event simulation with user-specified
variable time steps  The model is relatively
data-intensive and requires special effort for
validation and calibration  Its application in
detailed studies   of complex watersheds
may  require a team effort and highly trained
personnel.   SWMM  has been applied to
address various urban water quantity and
quality problems in many locations in the
United States and other countries  (Huber,
1989, Donigian and Huber,  1991)   In
addition   to   developing  comprehensive
watershed-scale planning, typical uses of
SWMM include predicting CSOs, assessing
the effectiveness of BMPs, providing input
to short-time- increment dynamic receiving
water quality  models,  and  interpreting
receiving  water quality  monitoring data
(Donigian and Huber, 1991)

The  Hydrological  Simulation Program -
FORTRAN   (HSPF)      HSPF   is   a
comprehensive package developed by the
U S EPA for simulating water quantity and
quality for a wide range of organic and
inorganic   pollutants  from  agricultural
watersheds  (Barnwell   and   Johanson,
1981)    The  model  uses  continuous
simulations of water balance and pollutant
generation, transformation, and transport
Time series   of  the  runoff  flow  rate,
sediment yield, and user-specified pollutant
concentrations can be generated  at any
point m the watershed   The model also
includes in-stream  quality components for
nutrient fate and transport, BOD, DO, pH,
phytoplankton, zooplankton, and benthic
algae  Statistical features are incorporated
in the model to allow for frequency-duration
analysis  of specific output parameters
Data requirements  for HSPF are extensive,
and   calibration   and  verification  are
recommended  The program is maintained
on  IBM  microcomputers  and  DEC/VAX
systems   Because of its comprehensive
nature, the  HSPF model  requires  highly
trained personnel  It is recommended that
its  application  to  real  case  studies  be
carried out as a team  effort  The HSPF
model has been extensively  used for both
screening-level   and  detailed  analyses,
                                                                                 21

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Compendium of  Watershed-Scale Models for TMDL Development	

including application to pesticide  runoff      1986), and analysis of best management
testing (Lorberand Mulkey, 1982), aquatic      practices (Donigian et al , 1983)
fate and transport testing (Mulkey et al ,
22

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                                3. OTHER MODELS
Many models have been  developed  to
assess pollutant movement, transformation,
and leaching in field-scale studies Like the
watershed-scale   models,  these  models
range in detail from empirical relationships
to physical  and  deterministic simulation
models  Many of these models provide for
detailed analysis of the  efficiencies  of
management practices  and evaluation of
alternative control options  Although these
models are not applicable to watershed or
subwatershed analysis, they may be used
in the TMDL process to assess  more
localized  problems  and to help develop
appropriate   nonpomt   source  pollution
control strategies

The  Occoquan Method   The  Occoquan
Method was developed by the Northern
Virginia  Planning  District  Commission,
Annandaie,  Virginia,  to  determine  the
design criteria required  to achieve a given
level of pollutant removal from development
areas  using  structural  practices   The
approach develops a site runoff coefficient
as  a function  of  imperviousness after
development   Overall  pollutant removal
efficiency for a given site is derived from
the type of control practices used and the
fraction of the total area controlled   This
method can be  used  for  reviewing  the
adequacy of proposed control practices It
was used in the  development of BMPs for
the Occoquan watershed (Northern Virginia
Planning District Commission, 1987)

Water Resources Evaluation of Nonpoint
Silvicultura!  Sources (WRENS)  WRENS
was  originally  developed  by  EPA  to
evaluate   the  effects  of   forest  and
silvicultural  activities  on  water  quality
(USEPA, 1980)  The method is compiled in
a   handbook  that   provides   various
quantitative  techniques   to   estimate
potential  changes in stream flow, surface
erosion  and  sediment yield, and water
temperature  The handbook also provides
directions on how to  compare alternative
silvicultural  management  practices  The
basic formulations of  this approach  are
similar to  those  developed  in  the  EPA
screening procedures

Chemicals,  Runoff,   and   Erosion from
Agricultural   Management  Systems
(CREAMS)  CREAMS is the most detailed
field-scale  model  available   to  evaluate
agricultural runoff  It was developed by the
U  S Department of Agriculture (USDA) to
provide detailed information necessary for
designing agricultural management systems
(Knisel,  1980)   CREAMS is  a  physically
based,   daily  simulation   model  that
estimates   runoff,   erosion/sediment
transport,  plant nutrients,  and  pesticide
yield from field-size areas   CREAMS  can
compare   relative  effects  of   different
agricultural  BMPs    The  model  is data-
intensive   and   requires  highly   trained
personnel   However,  it may be  applied
with  minimum  calibration  efforts    A
microcomputer  version   is   currently
available     The hydrology,   erosion and
sediment, and  pesticides  components of
CREAMS   were   used   to   develop
Groundwater Loading Effects of Agricultural
Management Systems (GLEAMS) (Leonard
et  al ,  1987)  to simulate  the vertical
                                                                                 23

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Compendium of Watershed-Scale Models for TMDL Development
movement  of  pesticides  and  evaluate
effects on groundwater quality

Pesticides Root Zone Model (PRZM)  PRZM
was developed by the EPA Environmental
Research Laboratory, Athens, Georgia, to
simulate   chemical   movement   in  the
unsaturated zone within and  below the
plant root zone (Carsel  et al , 1984)   It
considers  pesticide   application   and
accounts for  plant  uptake,  decay,  and
transformation,  and   the  dissolved,
adsorbed, and vapor phase concentrations
This model is linked to  other models to
simulate  the   transport  and   fate  of
pesticides and to assess the risk to drinking
water  wells.     PRZM  is  a   relatively
comprehensive model   requiring  highly
trained personnel   However, it requires  a
moderate level of  input data

The Water  Erosion  Prediction  Project
{WEPP). WEPP is  a simulation model using
daily time steps  It is the result of a multi-
agency  effort  to enhance researchers'
ability  to  model  erosion and   sediment
transport  processes  at field-scale  and
watershed levels (Laflan, Lane, and Foster,
1991).  The  model  is  currently  under
development and is intended to be used in
soil  erosion assessment and to provide
necessary information for siting agricultural
management practices on specific fields

Eutromod.   Eutromod  is a spreadsheet-
based   modeling   procedure  for
eutrophication management developed at
Duke University  and distributed by the
North American Lake Management Society
(Reckhow,  1990). It is a watershed and
lake model designed to estimate nutrient
loadings, various trophic state parameters,
and tnhalomethane concentrations in lake
water. The computation algorithms used in
Eutromod   were  developed   based  on
statistical relationships and a continuously
stirred tank reactor model  At present, the
model  is specific to  watersheds  in the
southeastern  United States with multiple
land uses including rural and urban areas,
feedlots, septic tanks, and discharges from
wastewater   treatment   plants  and
construction sites   Model results include
the most likely  predicted phosphorus and
nitrogen loading for the watershed and for
each land  use category  The model also
determines the  lake  response to various
pollution loading rates   The  spreadsheet
capabilities of the model allow graphical
representations  of the  results and  data
export  to  other spreadsheet  systems for
statistical analyses

Precipitation-Runoff    Modeling   System
(PRMS) PRMS is a deterministic physical-
process model developed by the USGS to
evaluate   the   impacts   of   various
combinations of precipitation, climate, and
land use  distribution  on  surface water
runoff,  sediment  yield,   and   general
watershed  hydrology  (Leavesley et al ,
1983)  It simulates watershed response to
normal and extreme rainfall and snowmelt
and determines changes in  water balance
relationships, flood peaks, and groundwater
recharge It includes several capabilities for
parameter  optimization  and  sensitivity
analysis  The model divides the watershed
into homogeneous   hydrologic-response
units (HRUs)  and can be applied to  both
agricultural and  urban land uses   Input
variables include  descriptive  data on the
physiography,   vegetation,   soil,  and
hydrologic and climatic characteristics  It
is,  however,  designed to  run with  data
retrieved directly from the USGS's National
Water   Data   Storage   and   Retrieval
(WATSTORE) system  The modular system
24

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Compendium of  Watershed-Scale Models for TMDL Development
approach provides an adaptable modeling
system for both management and research
applications  PRMS was initially developed
for  use  on mainframe computers   New
model components proposed by the USGS
as future additions to PRMS include water-
quality routines and  expanded saturated-
unsaturated  flow and groundwater flow
components

The  Unified Transport Model for Toxic
Materials  (UTM-TOX).   UTM-TOX  was
developed  by  the  Oak  Ridge  National
Laboratory for the analysis of hydrologic,
atmospheric,  and  sediment transport of
pesticides and toxic substances (Patterson
et al ,  1983)   This  model consists of a
multi-media   simulation  approach
Considering  a  chemical  release  to the
atmosphere  from  a  given source  (e g ,
stack, area, or line source), the model uses
mass balance  formulations to compute
chemical fluxes from the source through
the atmosphere, deposition on watersheds,
transport in surface runoff and percolation
through the soil profile,  and transport  in
sediment and streamflow    The  model
generates summary tables and plots of the
average  monthly  and  annual  chemical
concentrations in the various media  It also
considers biotic processes  and computes
chemical accumulation m stems, leaves,
and fruits of impacted vegetation  Limited
applications of this model were reported in
the literature due  primarily to the complex
nature of the model  and  the lack of user
support (Donigian and Huber, 1991)

Exposure   Analysis   Modeling   System
(EXAMS)  EXAMS was developed for the
USEPA to provide rapid evaluations of the
behavior of synthetic organic chemicals in
aquatic  systems (Burns and Cline, 1985)
The initial version  of EXAMS computes the
long term  results of  continual,  steady
discharges of single chemicals into typical
aquatic systems  The new version includes
updated  routines  which   consider  the
seasonal  variations  of  transport   and
transformation kinetics  and  computes the
fate and transport of  products resulting
from transforation reactions   The updated
version also includes capabilities for flexible
timing and durations of chemical loadings.
The model requires laboratory information
on  the  reactivity and  transformation of
chemicals  as well  as  state  variables
describing the transport mechanisms and
physical/chemical   properties   of   the
receiving water This model  is widely used
for exposure analysis and for deriving  basic
information  necessary  to perform health
and ecological risk assessments

The Water  quality  Analysis  Simulation
Program (WASP4)  WASP4 is a detailed
receiving water quality model supported by
the US  EPA (USEPA, 1988)   It allows
users to interpret and predict water quality
responses to natural phenomena and  man-
made   stresses   for   various  pollution
management decisions    WASP4  is  a
dynamic compartment  modeling  program
for  aquatic  systems,  including both the
water column and the underlying benthos
The model  includes  the   time-varying
processes of advection, dispersion,  point
and nonpomt mass loading,  and boundary
exchanges   WASP4 may be applied in two
modes  (1) EUTROWASP for nutrient and
eutrophication analyses  and (2) TOXIWASP
for analysis of toxic pollutants and metals
The flexibility of WASP4 is unique in that it
permits  the modeler to structure one, two,
or three dimensional model applications to
rivers,  lakes, estuaries, or  open  coastal
areas   The model's  computer  code  is
structured to permit easy development of
                                                                                25

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Compendium of Watershed-Scale Models for TMDL Development
new kinetic or reactive subroutines without
having  to  rewrite   large  sections  of
computer code   The mam advantage to
using  WASP4  is the  ability to  more
realistically  portray  the  relative  spatial
influence of each major pollutant source on
the receiving  water  as well  as  a more
accurate representation  of the transport/
water  quality  kinetics  phenomena  (i e
mixing and diurnal process) It may also be
useful  to assist in  designing long  term
monitoring programs for receiving waters
The model has been successfully applied to
a wide range of estuary water bodies  such
as the Peconic Bay,  Long Island,  and the
Bird River estuary, Maryland

Enhanced Stream Water Quality Mode!
(QUAL2E).   QUAL2E  is  an US  EPA
supported model.  It is a one dimensional
(longitudinal  water  quality model)  that
assumes steady state  flow  but allows
simulation  of   diurnal   variations  in
temperature or  algal  photosynthesis and
respiration.  QUAL2E simulates a series of
nonuniform segments that make up a river
reach  and  incorporates  the  effects  of
withdrawals,  branches, and  tributaries
Water quality parameters simulated include
conservative   substances,   temperature,
bacteria,  BOD,  DO,  ammonia,  nitrate,
nitrate and organic nitrogen, phosphate and
organic phosphorus, and algae  QUAL2E is
widely  used  for  stream  waste   load
allocations   and  discharge   permit
determinations in the  United States and
other countries (USEPA,  1992a)

Simplified  Method  Program  -  Toxics
(SMPTOX)     SMPTOX   is   an  USEPA
supported model    It  was developed to
provide   a  user-friendly  microcomputer
program  for  performing screening   level
modeling of toxic chemical concentrations
resulting from discharges from POTWs into
streams and  rivers  It provides a simplified
technique for performing load allocation for
dissolved oxygen/ammonia/CBOD  Because
of its simplistic approach, several versions
of SMPTOX are currently available (USEPA,
1992b)    The program  contains  a  full
screen editor to facilitate the entry and
modification of input data as well as high
resolution  graphics  to  present  model
results
26

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                              4. MODEL SELECTION
Watershed models are becoming more and
more integrated at various levels of water
quality  analysis    At  the  same time,
selecting the model that best matches the
project or objective in hand is  becoming
difficult  as  more   models  are  being
developed     The   watershed   models
presented in the previous section cover a
wide range of functions and can be applied,
either   directly  or   with   minimum
modification, to  the  majority of planning
problems  associated  with  point  and
nonpomt source  pollution  Selection of a
watershed or water quality model may be
considered an important decision process,
not only because of the time and  resources
a modeling effort involves, but also because
of  the  wide  variety  and   amount  of
information a water  quality project may
require

4.1 Model Characteristics

In addition to information presented in the
previous sections  of this  compendium,
relevant characteristics generally associated
with   model   selection   for   specific
applications are presented in this section
Tables  4, 5, and 6 present the basic
simulation functions used in each model to
generate pollutant loadings   Most water-
shed models include three components  a
hydrology component, which estimates the
quantity  of   runoff  and   streamflow
generated   from  the  watershed   or
subwatersheds,  an  erosion and  sediment
component, which derives the amount of
sediment delivered to  a  receiving water
body, and  a  quality  component,  which
computes the pollutant loadings  Tables 4-
6 also present the type of pollutant handled
by  each model and  the  corresponding
computation time steps

As shown in Tables 4-6, most models are
based on similar mathematical formulations
The   curve   number   equation   (CNE)
developed by the USDA-SCS is widely used
for  simulating runoff  and  stream flows
(e g , NPSMAP, GWLF, P8-UCM, AGNPS,
STORM, SWRRBQ), and the Universal Soil
Loss Equation (USLE) is commonly used for
determining erosion and sediment  yield
from rural areas or watersheds (e g , EPA
screening   procedures.   Water  Screen,
Watershed,   SLOSS-PHOSPH,   GWLF,
AGNPS,  STORM,  SWRRBQ)    Pollutant
loadings from  rural   areas  are  often
calculated based on loading functions or
potency  factors  (e g ,  EPA  screening
procedures,  Water   Screen,   AGNPS,
SWRRBQ, HSPF)   For urban areas, unit
area loading rates (e g  , GWLF) or build-up
and  washoff  functions  (e g ,  STORM,
SWMM) are widely used   The advantage
of the CNE- and USLE-based models is that
detailed default parameters are available for
a wide variety  of soil  conditions and
agricultural  management techniques  The
differences  among models using similar
simulation functions reside in the degree of
spatial discretization they use, the number
                                                                               27

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                           Table 4. A Descriptive List of Model Components - Simple Methods
Model
EPA Screening
Procedures
The Simple
Method
Water Screen
Watershed
FHWA
WMM
SLOSS/PHOSPH
Regression
Mam Land
Use
Mixed
watershed
Urban
Mixed
watershed
Mixed
watershed
Highways
Mixed
watershed
Rural
Urban
Hydrology
N/A
Runoff coefficient
N/A
N/A
Runoff coefficient,
observed data
Runoff coefficient
N/A
N/A
Erosion/
Sediment
USLE-
MUSLE
N/A
USLE
USLE
N/A
N/A
USLE
N/A
Pollutant
Load
Loading functions,
potency factors
Mean
concentration
Loading functions,
potency factors
Unit area loadings
Median
concentration
Event mean
concentration
Loading functions
Regression
equations
Pollutants
Wide range1
NURP data
TSS, P, metals,
O&G
N, P, organics
Wide range1
TSS, N, P
Organics, metals
N, P, lead,
zinc
P
TSS, N, P,
COD, metals
Time
Scale
Mean annual
Variable
(annual,
monthly,
event)
Mean annual
Annual
Storm event
Annual
Annual
Storm event
I
I
                                                                                                                         0?
                                                                                                                         I
                                                                                                                         I
                                                                                                                         «•
                                                                                                                         i
                                                                                                                         I
                                                                                                                         t
                                                                                                                         i
                                                                                                                         s
                                                                                                                         I
                                                                                                                         i
1 Depends on available pollutant parameters and default data

 N     Nitrogen
 0 + G Oil and gas
 P     Phosphorus
 TSS   Total suspended solids
 COD  Chemical oxygen demand

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                                  Table 5  A Descriptive List of Model Components - Mid-Range Models
Model
NPSMAP
GWLF
P8-UCM
SIMPTM
Auto-QI
AGNPS
SLAMM
Main Land
Use
Mixed
watershed
Mixed
watershed
Urban
Urban
Urban
Agriculture
Urban
watershed
Hydrology
SCS curve number
SCS curve number
SCS curve number
-modified
TR20
Trapezoidal
hyetograph
Water balance
SCS curve number
Small storm-based
coefficient
Erosion/
Sediment
N/A
Modified USLE
N/A
Modified Yalm
equation
N/A
Modified USLE
N/A
Pollutant
Load
Runoff
concentration
Unit loading
rates
Nonlinear
accumulation
Nonlinear
accumulation
Accumulation
and washoff
Potency
factors
Nonlinear
accumulation
and washoff
Pollutants
N, P
N, P
TSS, N, P,
metals
Wide Range1
Wide Range1
N, P
N, P, COD
bacteria,
metals
Time
Scale
Continuous
Continuous
Storm
sequence
Storm
sequence
Storm event,
Continuous
Storm event
Continuous
                                                                                                                                   o
                                                                                                                                   I
                                                                                                                                   I
                                                                                                                                   I
                                                                                                                                  t
1 Depends on available pollutant parameters and default values

 N     Nitrogen
 0 + G Oil and gas
 P     Phosphorus
 TSS   Total suspended solids
 COD  Chemical oxygen demand

-------
                           Table 6. A Descriptive List of Model Components - Detailed Models
Model
ANSWERS
SWMM
HSPF
STORM
SWRRB
DR3M
Main Land
Use
Agriculture
Urban
Mixed
watershed
Urban
Agriculture
Urban
Hydrology
Distributed storage
model
Nonlinear reservoir
Water balance of land
surface and soil
processes
Runoff coefficient -
SCS curve numbers -
Unit hydrograph
SCS curve number
Surface storage
balance
kinematic wave
method
Erosion/
Sediment
Detachment
transport
equations
Modified USLE
Detachment/
washoff
equations
USLE
Modified USLE
Related to runoff
volume and peak
Pollutant
Load
Potency factors
(correlation with
sediment)
Buildup/washoff
functions
Loadmg/washoff
functions and
subsurface
concentrations
Buildup/washoff
functions
Loading functions
Buildup/washoff
functions
Pollutants
N/A
Wide range1
Wide range1
P, N, OD,
metals
N, P, OD,
metals,
bacteria
TSS, N, P,
organics,
metals
Time
Scale
Storm event
Storm event,
continuous
Storm event,
Continuous
Continuous
Continuous
Continuous
s
                                                                                                                         o
                                                                                                                         -s

                                                                                                                         I
                                                                                                                         I
                                                                                                                         $
                                                                                                                         i

1 Depends on available pollutant parameters and default values

 N     Nitrogen
 0 + G Oil and gas
 P     Phosphorus
 TSS   Total suspended solids
 COD  Chemical oxygen demand


-------
Compendium of Watershed-Scale Models for TMDL Development
of processes for which they account, and
the computational time steps they use

Many of the simple methods do not take
hydrologic  processes  into account  when
simulating pollutant loads  When dealing
with  urbanized  areas,  simple  methods
usually generate runoff based on empirical
or statistical relationships between runoff
coefficients   and    the  degree   of
imperviousness (e g , the Simple Method,
FHWA, and WMM) It is, however, difficult
to extrapolate such relationships to rural
and agricultural areas

Detailed   models  use  more  complex
formulations  for simulating   runoff and
sediment yield  The hydrology component
generally involves a  set of deterministic
equations to represent the elements of the
water balance equation  (e g , infiltration,
evapotranspiration, groundwater recharge
and/or  seepage,  depression  storage)
These   models   also   use   a   physical
description of the erosion and  sediment
yield mechanisms  (e g ,  soil detachment,
transport, and deposition)  Predictions of
pollutant washoff are usually made  based
on  exponential  decay  functions  (e g ,
SWMM)  with hourly time steps  Default
values for  parameters are pollutant- and
site-specific and therefore  may not  be
readily available, making calibration difficult
and  time-consuming     In  most  cases,
additional  laboratory  testing  and  field
measurement may be required

The type and amount of input data required
for operation, calibration, and verification of
the model and the output results should be
considered in the model selection process
Depending on the type of formulations the
model  uses, input data  may  range  from
simple watershed characteristics to hourly
meteorological   parameters,   pollutant
transformation kinetic coefficients, and field
monitoring data    Tables  7, 8,  and 9
present a  brief summary  of input and
output information for each of the models
reviewed   Novotny and  Chesters  (1981)
have   developed   three  sets  of  input
parameters that  may  be required  for a
typical modeling  application (Table 10)
Interpretation of the type and amount of
data  required,  along  with  information
contained in the preceding tables, may be
used to evaluate the time  and resources
required to apply a given model for a given
situation or project  For a detailed listing of
input requirements, please refer directly to
the model documentation

Watershed models are usually developed to
target  a  specific  setting,  characterized
primarily by land use or land activity  Few
models  are   developed   to   evaluate
watersheds with mixed land uses  Among
the detailed models, HSPF appears to  be
the most versatile for watersheds  with
complex  land use/land cover   SWMM,
STORM,  and  DR3M-QUAL  are  designed
primarily for urban areas, while ANSWERS
and  SWRRB  are  primarily  agricultural
models   Among the  mid-range models,
NPSMAP and GWLF are the two  models
that account for both rural and agricultural
watersheds The  GWLF model offers the
possibility  of  generating  long-term  time
series of pollutant loadings at various time
steps,  allowing analysis  of seasonal and
inter-annual variabilities GWLF also allows
evaluation  of  watershed   response  to
changes in land use patterns and point and
nonpomt source loadings  Urban  models
such as P8-UCM, SIMPTM, and SLAMM
were   mainly  designed   for  evaluating
management practices to  control  urban
stormwater runoff  Simple  methods use
                                                                                 31

-------
Jo
Nj
  Table 7. Input and Output Data - Simple Methods
                       Models
              EPA Screening Procedures
              The Simple Method
              Regression
              SLOSS/PHOSPH
              Water Screen
              Watershed
              FHWA
              WMM
            Main Input Data
Watershed and land use data
Loading factors (default values)
Annual rainfall data
Land use and imperviousness data
Pollutant mean concentration
BMPs removal efficiencies
Mean annual rainfall
Mean minimum January temperature
Drainage areas and land use
Percent imperviousness
Rainfall erosivity factor
Soil, crop, topography, and land use data
Rainfall erosivity factor
Watershed and land use data
Loading factors (default values)
Rainfall erosivity factor
Land use and soil parameters
Unit loading rates
BMP cost information	
Site and receiving water data
Flow and storm event concentrations
Land use and soil data
Annual precipitation and evaporation
Inputs from baseflow and precipitation
Event mean concentrations in runoff
Reservoir, lake or stream hydraulic
  characteristics
Removal efficiencies of proposed BMPs
           Output Information
Mean annual sediment and pollutant loads
Runoff volume and pollutant
 concentration/load, storm or annual
Mean annual storm event load and
 confidence interval
Mean annual loads of sediment and
phosphorus
Mean annual sediment and pollutant loads
Mean annual pollutant loads
BMP cost-effectiveness
Statistics on storm runoff and
 concentrations
Impacts on receiving water
Annual urban and rural pollutant loads
 from point and nonpoint sources,
 including septic tanks
Load reductions from combined effects of
  multiple BMPs
In-lake nutrient concentrations as related
  to trophic state, also concentrations
  of metals                      "^r
I
i
o

 i
 I

I

-------
                           Table 8. Input and Output Data - Mid-Range Models
                                                     f
                                                     o
                                                     I
                                                     I
                                                                                                                   I
                                                                                                                   I
                                                                                                                   I
                                                                                                                   i
                                                                                                                   f
 Models
NPSMAP
GWLF
P8-UCM
SIMPTM
Auto-QI
AGNPS
SLAMM
                             Mam Input Data
           Meteorologic and hydrologic data, hourly or daily
             maximum one year
           Watershed and channel parameters
           Point sources and pollutant parameters (e.g , decay)
           Meteorologic and hydrologic data, daily
           Land use and soil data parameters
           Nutrient loading rates
Meteorologic and hydrologic data, hourly storm or
 storm sequence
Land use and soil parameters
BMP information
Rainfall event statistics
Watershed parameters
Accumulation and washoff rates (default values)
Hourly/daily rainfall
Watershed and land use data
BMP removal rates
Watershed, land use, management, and soil data
Rainfall data, topography
BMP removal data
           Hourly rainfall data
           Pollution source characteristics, areas, soil type,
             imperviousness, and traffic
           Structure characteristics
                                                                Output Information
                                                    Runoff and nutrient loadings
                                                    Pollution load allocations
                                                    Monthly and annual time series of runoff,
                                                     sediment, and nutrients
Daily runoff and pollutant loads
BMP removal efficiencies
Storm runoff volume and hydrograph
 characteristics
TSS/sediment and pollutant washoff
Continuous or storm event simulation of
 runoff and selected pollutants
Storm runoff volume and peak flow
Sediment, nutrient, and COD concentrations
                                                    Pollutant load by source area
                                                    BMP evaluation and cost estimates

-------
                             Table 9. Input and Output Data - Detailed Models
I
  Models
                  Main Input Data
                                                                             Output Information
STORM
Hourly rainfall data
Buildup and washoff parameters
Runoff coefficient and soil type
                                                                 Event-based runoff and pollutant loads
                                                                 Storage and treatment utilization and
                                                                  number of overflows
                                                                 Hourly hydrographs and pollutographs
                                                                                                        I
ANSWERS
Hourly rainfall data
Watershed, land use, and soil data
BMP design data
                                                                 Predicts storm runoff (volume and peak flow),
                                                                 Sediment detachment and transport
                                                                 Analysis of relative effectiveness of
                                                                  agricultural BMPs
DR3M
Meteorologic and hydrologic data
Watershed characteristics related to runoff
Channel dimensions and kinematic wave parameters
Characteristics of storage basins
Buildup and washoff coefficients
                                                                 Continuous series of runoff and pollutant yield
                                                                  at any location in the drainage system.
                                                                 Summaries for storm events
                                                                 Hydrographs and pollutographs
I

SWRRB
Meteorologic and hydrologic data
Watershed and receiving waterbody parameters
Land use and soil data
Ponds and reservoir data
                                                                 Continuous water and sediment yield
                                                                 Peak discharge
                                                                 Water quality concentrations and loads
SWMM
Meteorologic and hydrologic data
Land use distribution and characteristics
Accumulation and washoff parameters
Decay coefficients
                                                                 Continuous and event-based runoff and
                                                                  pollutant loads
                                                                 Transport through streams and reservoirs
                                                                 Analysis of control strategies
HSPF
Meteorologic and hydrologic data
Land use distribution and characteristics
Loading factors and washoff parameters
Receiving water characteristics
Decay coefficients
                                                                 Time series for runoff and pollutant loadings
                                                                 Analysis of impacts on receiving water
                                                                 Analysis of controls

-------
Compendium of Watershed-Scale Models for TMDL Development
                     Table 10. Input Data Needs for Watershed Models
                             (after Novotny and Chesters, 1981)
             System Parameters

             Watershed size
             Subdivision of the watershed into homogenous subareas
             Imperviousness of each subarea
             Slopes
             Fraction of impervious areas directly connected to a channel
             Maximum surface storage (depression plus interception storage)
             Soil characteristics including texture, permeability, credibility, and composition
             Crop and vegetative cover
             Curb density or street gutter length
             Sewer system or natural drainage characteristics
             State Variables

             Ambient temperature
             Reaction rate coefficients
             Adsorption/desorption coefficients
             Growth stage of crops
             Daily accumulation rates of litter
             Traffic density and speed
             Potency factors for pollutants (pollutant strength on sediment)
             Solar radiation (for some models)
            Input Variables

            Precipitation
            Atmospheric fallout
            Evaporation rates
                                                                                              55

-------
Compendium of Watershed-Scale Models for TMDL Development
generic empirical relationships that can be
used  in  both  rural and urban  settings
provided site-specific or default values are
available.

Model applications may be  classified as
screening,   intermediate,   or   detailed
depending on the focus and  objectives of
the application.  Simple methods are most
frequently used for screening applications,
however, mid-range and detailed  models
may allow for a wider range of applications
Screening   applications  are  generally
performed at the  preplanning level, with
specific objectives such as comparisons of
the  relative  contribution  of  point  and
nonpoint sources using a relatively limited
set of available  information   Screening
analyses may consider a broad range of
land use types and sources and  may be
performed  at various stages of  project
development (e g , planning, evaluation of
alternatives,  preliminary  design)   At the
planning level, screening applications may
be  directed  toward scoping the  project
objective and  identifying  general  areas
where controls or additional sampling may
be required.

Intermediate  applications provide  a  more
detailed  description  of the geographic
variables contributing to nonpoint pollution,
in addition to  consideration of multiple point
sources.  Intermediate  applications  may
assist in identifying  specific point and
nonpoint source activities and in preliminary
selection  of pollution  control   options
incorporating a  higher degree of spatial
variation within land uses

As it  becomes necessary  to accurately
distinguish   differences   in  pollutant
characteristics from multiple  source areas,
pollutant behavior is considered  in  more
detail and a more  mechanistic description
of pollutant generation, transformation, and
removal  by various control practices  is
required      Detailed   applications   are,
therefore,  necessary  to  provide  either
storm-based  or  continuous simulation of
water and water quality processes and to
assist  in  developing design  criteria  for
achieving project objectives

The  potential  range of applications of
watershed models m planning, evaluation of
management measures, and  analysis of
impacts on the quality of receiving waters
is illustrated in Tables 11, 12, and 13  The
tables show that the majority of the models
may   be   used   for   screening-level
applications    The simple  methods  in
particular  provide  only   an   order-of-
magnitude estimate on an annual basis and
therefore   are   limited  to   screening
applications at the planning level  Some of
the  mid-range   models  (e g ,  GWLF,
NPSMAP, and  AGNPS)  incorporate point
and nonpoint source pollution routines and
are also good  candidates  for  screening
activities  SLAMM, P8-UCM, and SIMPTM
are primarily urban runoff models, and their
application   to   evaluation   of   urban
stormwater control practices and strategies
may be  useful  at an intermediate  level
SWMM,   HSPF,  DR3M,  STORM,  and
SWRRB  stand  out from  the  others as
models capable  of providing  a detailed
indication of the contribution of pollutants
from various point and nonpoint sources
Their  simulation  capabilities  allow  for
evaluation   of  control  strategies  and
development of design criteria

Application  of  detailed  models  such as
HSPF and SWMM for screening purposes,
using estimated default values for a number
of parameters, may reduce time and input
36

-------
Compendium of Watershed-Scale Models for TMDL Development
requirements    However, representative
default  values  for  many of the detailed
models  are difficult to obtain  In addition,
their accuracy as screening tools may be
jeopardized   by   replacing  mechanistic
equations with their simplified  forms and
including  inappropriate   default  values
Urban stormwater runoff models, such as
SWMM, HSPF, SLAMM,  P8-UCM,  and
DR3M-QUAL,  are  capable of  providing
design criteria for a number of structural
practices   Models  with  such capabilities,
however,  are data-intensive and  require
trained professionals to operate the model,
select   appropriate  default values,  and
interpret the results
                        4.2 Model Calibration and Verification

                        The results of watershed simulations are
                        more    meaningful   when   they   are
                        accompanied by some sort of confirmatory
                        analysis   The capability of any model to
                        accurately depict water quality conditions is
                        directly related to the accuracy of input
                        data and the  level of expertise required to
                        operate the  model    It  is  also  largely
                        dependent on the amount of data available
                        Detailed  models  lacking  the required
                        calibration and verification data are limited
                        in accuracy.
           Table 11  Range of Application of Watershed Models - Simple Methods
Simple
Methods
EPA Screening
The Simple Method
Regression
SLOSS/PHOSPH
Water Screen
Watershed
FWHA
WMM
Watershed Analysis
Screening
•
•
•
o
•
•
•
•
Intermediate
-
-
-
-
-
-
-
O
Detailed
-
-
-
-
-
-
-
-
Control Analysis
Planning
-
O
-
-
-
0
o
€
Design
-
-
_
-
-
-
-
-
Receiving
Water
Quality
O
-
-
-
-
-
O
€
           High
Medium
O Low
                    - Not Available
                                                                                  37

-------
Compendium of Watershed-Scale Models for TMDL Development
          Table 12 Range of Application of Watershed Models - Mid-Range Models
Mid-Range
Methods
NPSMAP
GWLF
P8-UCM
SIMPTM
Auto-QI
AGNPS
SLAMM
Watershed Analysis
Screening
•
•
•
o
•
•
•
Intermediate
O
€
€
€
•
•
G
Detailed
0
o
G
G
0
O
0
Control Analysis
Planning
G
-
O
€
O
•
•
Design
-
-
•
O
o
o
o
Receiving
Water
Quality
0
_
-
-
0
0
0
             High
  Medium
O Low
           - Not Available
           Table 13.  Range of Application of Watershed Models - Detailed Models
Detailed
Methods
STORM
ANSWERS
SWRRBQ
DR3M-Q
SWMM
HSPF
Watershed Analysis
Screening
•
•
0
G
G
G
Intermediate
•
•
•
•
•
•
Detailed
O
€
•
•
•
•
Control Analysis
Planning
•
•
•
•
•
•
Design
O
O
O
C~
G
0
Receiving
Water
Quality
O
O
G
G
-
•
             High
Q Medium
O Low
           -  Not Available

-------
 Compendium of  Watershed-Scale Models for TMDL Development
Calibration   involves   minimization   of
deviation   between   measured   field
conditions and model output by adjusting
parameters of the model  (Jewell  et al ,
1978)  Data required for this step are a set
of   known  input  values  along   with
corresponding  field observation  results
The  results  of  the sensitivity  analysis
provide information as to which parameters
have the greatest effect on  output  For the
best  results,   CSO  models  should  be
calibrated during storm events as opposed
to dry flow periods (Water Pollution Control
Federation, 1989)

Verification involves the use of a second
set of independent information to check the
model  calibration   The  data  used  for
verification   should   consist   of   field
measurements of the same type as the data
output from the model   Specific features
such as mean values,  variability, extreme
values,  or  all predicted values may  be of
interest to  the modeler and require testing
(Reckhow and Chapra, 1983)  Models are
tested  based  on  the  levels  of  their
predictions,   whether  descriptive   or
predictive  More accuracy  is required of a
model designed for absolute versus relative
predictions    If the model is calibrated
properly, the  model  predictions will be
acceptably close to the field observations

Observed data for model  calibration and
verification  may,  in  many  cases,  be
insufficient or unavailable  Model selection
must be based on an assessment of the
available data Screening-level applications
may be possible with limited input data  As
noted  by Donigian and Rao (1988), most
models are more accurate when applied in
a relative rather than an absolute manner
Model output data concerning the relative
contribution  of  a  watershed  to overall
pollutant loads is  more reliable than an
absolute prediction of the impacts of one
control alternative  viewed alone   When
examining model  output from watershed-
pollution sources, it is important to note
three factors that may influence the model
output and  produce  unreasonable  data
First,  suspect  data  may  result  from
calibration  or verification  data that are
insufficient   or   inappropriately  applied
Second, any given model, including detailed
models, may not represent enough detail to
adequately describe existing conditions and
generate reliable output  Finally, modelers
should remember that all  models  have
limitations and the selected model may not
be capable of simulating desired conditions
Model results must therefore be interpreted
within  the limitations of their testing and
their  range  of application    Inadequate
model calibration and verification can result
in spurious model results, particularly when
used  for absolute   predictions     Data
limitations may require that model results
be used only for relative comparisons
                                                                                  39

-------
                                5. REFERENCES
Addiscott, T.  M.,  and  R  J  Wagenet
1985. Concepts of solute leaching in soils
A review of modeling approaches  Journal
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Alley, W.M 1986  Summary of experience
with the distributed  routing rainfall-runoff
model   (DR3M).   In   Urban  Drainage
Modeling, ed. C   Maksimovic and  M
Radojkovic, pp 403-414 Pergamon Press,
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Amy, G.R., R  Pitt, W L Singh, Bradford,
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management  for  urban runoff. , U   S
Environmental   Protection  Agency,
Washington,  D.C ,   EPA  440/9-75/004
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Arnold, J.G., J R. Williams, A D  Nicks, and
N.B.  Sammons  1989.  SWRRB,  a  basin
scale simulation model for soil and  water
resources management Texas A&M Press

Barnwell, T.O., and R  Johanson 1981
HSPF:  A comprehensive  package  for
simulation of watershed  hydrology and
water quality. Nonpoint pollution control:
 Tools  and  techniques for the future.
Interstate Commission  on  the Potomac
River Basin, Rockville, MD.

Beasley, D B. 1986  Distributed parameter
hydrologic and  water  quality modeling
Agricultural  Nonpoint Source Pollution:
Model  Selection  and  Application,  ed
 Giorgmi and F. Zmgales. pp  345-362
Bird,  B L.  and KM  Conaway   1985
WATER  SCREEN  -  A  microcomputer
program  for  estimating  nutrient  and
pollutant  loadings In Proceedings of the
Stormwater and Water Quality Model Users
Group  Meeting, April 12-13,  1984  ed
TO  Barnwell, pp  121-174  EPA-600/9-
85-0013

Biswas,  A K   1975     Mathematical
modelling   and environmental  decision-
making Ecological Modelling 1 31-48.

Burns, LA,  and  DM   Clme    1985
Exposure  Analysis  Modeling  System -
Reference  manual for EXAMS  II US
Environmental   Protection  Agency,
Environmental  Research   Laboratory,
Athens, Georgia  EPA/600/3-85/038.

Camp, Dresser, and  McKee (COM) 1992.
Watershed  Management  Model user's
manual,  version  2  0,  Prepared  for the
Florida  Department  of  Environmental
Regulation, Tallahassee, FL

Carsel R F , C.N  Smith, L A Mulkey, J D
Dean, and  P Jowise.   1984    User's
manual for the Pesticide Root Zone Model
(PRZM): release  1     US Environmental
Protection Agency, Environmental Research
Laboratory, Athens,  GA  EPA-600/3-84-
109

Clark, W C , D D  Jones, and C S Hollmg
1979  Lessons for ecological policy design
A case study of ecosystem management
Ecological Modelling 7 1-53
 40

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Compendium of Watershed-Scale Models for TMDL Development
Dillaha,  TA   1992    Nonpomt  source
modelling for evaluating the effectiveness
of best  management practices  NWQEP
Notes 52(March) 5-7

Dillaha, T A , C D Heatwole, M R Bennett,
S  Mostaghimi, V O  Shanholtz, and B B
Ross  1988   Water quality modeling for
nonpoint source pollution control planning:
Nutrient transport.    Virginia  Polytechnic
Institute and  State University,  Dept  of
Agricultural Engineering  Report No  SW-
88-02

Donigian, A S , G C Imhoff, B R Bicknell
1983   Modeling  water quality and the
effects of BMPs in  Four Mile Creek, Iowa.
U S.  Environmental  Protection Agency,
Environmental  Research   Laboratory,
Athens,  GA

Donigian,  AS.,  D W  Meier, and  P P
Jowise.    1986    Stream transport and
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A methodology.  Environmental Research
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EPA/600/3-86-011

Donigian, A S  , and W C Huber  1991
Modeling of nonpoint source water quality
in urban  and  non-urban  areas    U S
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EPA/600/3-91/039

Donigian, A.S  , and  PSC  Rao   1988
Selection,  application, and validation  of
environmental models. Draft  Prepared for
presentation   at   the  International
Symposium on Water Quality Modeling of
Agricultural Non-Point Sources Utah State
University, Logan, UT  June 19-23, 1988.

Federal  Highway  Administration,  1990
Pollutant  loadings  and impacts   from
highway stormwater  runoff  Research,
Development,   and  Technology   U S
Department of Transportation, McLean, VA

Haith, DA, and LL  Shoemaker 1987
Generalized watershed loading functions for
stream  flow nutrients  Water  Resources
Bulletin  107(EEI) 121-137

Huber, WC   1989   User  feedback  on
public domain  software   SWMM  case
study   In  Proceedings  of  the  Sixth
Conference  on   Computing   in   Civil
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Huber, WC and RE  Dickinson 1988
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Hydrologic  Engineering   Center  1977.
Storage,  Treatment,  Overflow,  Runoff
Model,    STORM,  User's   manual
Generalized Computer  Program  723-S8-
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Davis, CA

Jewell, T.K , T  J Nunno, and  D  D Adrian
1978     Methodology   for   calibrating
stormwater  models.   Journal  of  The
Environmental  Engineering Division,  104
485

Knisel W G 1980 CREAMS,  A field scale
model for Chemicals, Runoff, and Erosion
from Agricultural Management  Systems.
U S    Department  of  Agriculture,
Conservation Research Report No 26

Laflan J M., L.J. Lane, and  G R  Foster
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Water Conservation  46 (1). 34-38
                                                                              41

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Compendium of Watershed-Scale Models for TMDL Development
Leavesley,   G H,   R W   Lichty,  B M
Troutman,  and   LG   Saindon   1983
Precipitation-runoff  modeling   system
User's manual. U S  Geological  Survey,
Central Region, Water Resources Division,
Denver, CO.    Water-Resources Inves-
tigation 83-4238

Leonard, R.A , W G  Knisel, and D A Still
1987.  GLEAMS.  Groundwater  Loading
Effects   of   Agricultural   Management
Systems  Transactions of the ASAE 31 (3)
776-788.

Lorber, M.N , and  L A Mulkey  1982  An
evaluation of three pesticide runoff loading
models. Journal of Environmental Quality
11(3): 519-529.

McElroy, A.D , S W Chiu, J W Nabgen, A
Aleti,  R.W  Bennett   1976     Loading
functions for assessment of water pollution
for non-point sources  U S Environmental
Protection  Agency   EPA 600/2-76/151
{NTIS PB-253325)

Mills,  W.B.    1985     Water  quality
assessment: A screening procedure for
toxic and conventional pollutants in surface
and ground water. Part 1  Environmental
Research Laboratory, U S  Environmental
Protection   Agency,   Athens,  GA
EPA/600/6-85/002a.

Nix,  J.S.  1991.  Applying urban runoff
models.   Water  Environment  and
Technology, June 1991

Northern  Virginia   Planning   District
Commission   1987   BMP handbook  for
the Occoquan watershed Northern Virginia
Planning  District Commission, Annandale,
VA.
Novotny, V  and G  Chesters    1981
Handbook of nonpoint pollution-  Sources
and management.  Van Nolstrand Remhold
Company, New York, NY

Omicron  Associates   1990   Nonpoint
Pollution  Source Model for Analysis and
Planning  (NFSMAP)  -   Users  manual
Omicron Associates, Portland, OR

Palmstrom,   N ,  and W W  Walker,  Jr
1990 P8 urban catchment model- User's
guide.   Program   documentation,   and
evaluation  of  existing  models,  design
concepts,  and  Hunt-Potowomut  data
inventory The  Narragansett Bay Project
Report No NBP-90-50

Panuska, J C ,  ID  Moore, and L A
Kramer      1991     Terrain   analysis
Integration  into the agricultural  nonpoint
source (AGNPS) pollution model   Journal
of Soil and  Water Conservation 46(1)  59-
64
Patterson,  M
Sjoreen,  M G
D M  Hetrick,
Randon  1983
TOX, A unified
by  Oak  Ridge
Ridge, TN, for
Substances
R ,   T J.  Sworski,  A L
Brownman, C C  Coutant,
 B D  Murphy,  and  R J
 A user's manual for UTM-
transport model.  Prepared
 National Laboratory, Oak
U S  EPA Office of Toxic
 Pitt,  R   1986     Runoff  controls  in
 Wisconsin's priority watersheds In Urban
 Runoff Quality, ed Urbonas, B , and L A
 Roesner  Proceedings of the  Engineering
 Foundation Conference  on  Urban Runoff
 Quality   (ASCE),  June  22-27,   1986
 Henniker, NH

 Reckhow,   KH    1990   EUTROMOD
 Watershed and  lake modeling software.
 42

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Compendium of  Watershed-Scale Models for TMDL Development
Software package No. 1. North American
Lake Management Society, Alachua, FL

Reckhow, K H , and S C   Chapra  1983
Confirmation  of water  quality models
Ecological Modelling 20 113-133

Schueler,  T   1987    Controlling urban
runoff: A practical manual for planning and
designing urban  BMPs    Metropolitan
Washington   Council  of  Governments,
Washington, DC

Stewart,   B A ,  DA   Woolhiser,  W H
Wischmeier, J H  Cara, and  M H  Frere
1975  Control of  Water Pollution  From
Croplands.  Vol  I  U S   Environmental
Protection  Agency,   Washington,   DC
EPA600/2-75/026a

Sutherland, R  C , D  L Green, and S  L
Jelen    1990   Simplified   Paniculate
Transport Model.  User's manual OTAK,
Inc , Lake Oswego, OR

Tasker,  G D ,  and N E  Driver    1988
Nationwide regression models for predicting
urban runoff water quality at unmonitored
sites      Water  Resources  Bulletin
24(5) 1091-1101

Terstnep, M L , M  T  Lee, E P  Mills, A
V  Greene, and  M  R  Rahman   1990
Simulation of urban runoff and pollutant
loading from the greater Lake Calumet area,
Prepared  by the Illinois State Water Survey
for the  U S  Environmental  Protection
Agency,  Region  V,    Water  Division,
Watershed Management Unit, Chicago, IL

Tim, U S  , S Mostaghimi, V O  Shanholtz,
and N Zhang   1991   Identification of
critical nonpomt pollution source area using
geographic  information   systems   and
simulation modeling  In Proceedings of the
American Society of Agricultural Engineers
(ASAE)   International  Winter  Meeting,
Albuquerque, New Mexico, June  23-26,
1991

USEPA    1980   An  approach to water
resources  evaluation   of  nonpoint
silvicultural   sources  (A   procedural
handbook). U S  Environmental Protection
Agency,   Environmental   Reserach
Laboratory,  Athens,  GA    EPA  600/8-
80/012

USEPA  1988  WASP4, A hydrodynamic
and water quality model - Model theory,
user's manual, and programmer's guide
U S   Environmental  Protection Agency,
Environmental  Research   Laboratory,
Athens, Georgia  EPA 600/3 87/039

USEPA  1991 a   Workshop on the Water
Quality-based Approach  for Point Source
and  Nonpoint Source  Controls.    U S
Environmental  Protection  Agency   EPA
503/9-92-001

USEPA    1991b    Guidance  for water
quality-based  decisions:    The  TMDL
process   U S  Environmental  Protection
Agency  EPA 440/4-91-001

USEPA    1992a    Technical guidance
manual   for  performing   waste   load
allocations - Book II  Streams and rivers
(Draft)  U S  Evironmental   Protection
Agency, Washington, DC

USEPA    1992b     Simplified Method
Program   -  Toxics  (SMPTOX),   User's
manual    U S  Environmental  Protection
Agency,   Monitoring  and  Data Support
Division, Washington, DC
                                                                              43

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Compendium of  Watershed-Scale Models for TMDL Development
Walker, J.  F., S. A  Pickard, and W C
Sonzogni  1989.  Spreadsheet watershed
modeling  for  nonpomt-source  pollution
management in a Wisconsin basin  Water
Resources Bulletin 25(1).139-147

Water Pollution Control Federation. 1989
Combined  sewer  overflow  abatement:
Manual of practice no. FD-17.

Young, R A , C A. Onstad, D D Bosch, and
W.P.   Anderson   1986   Agricultural
nonpoint source pollution model: A
watershed analysis tool U S  Department
of  Agriculture,   Agricultural  Research
Service, Morris, MN

Young, R A , C A Onstad, D D Bosch, and
WP  Anderson    1989     AGNPS   A
nonpomt-source   pollution   model   for
evaluating  agriculture watersheds  Journal
of Soil and Water Conservation  44 168-
173
44

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            APPENDIX
WATERSHED-SCALE MODEL - FACT SHEETS

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                          EPA Screening Procedures
 1  Distributor

 Center for Exposure Assessment
   Modeling
 U S  Environmental Protection Agency
 Environmental Research Laboratory
 Athens, Georgia 30613
 (404) 546-3123

 2  Type of Modeling:

 •  Not a computer program, consists of
   a series of equations/techniques
 •  Pollutant loadings
 •  Multiple diffuse source
 •  Annual time steps, but may be used
   for storm events
 •  Screening application

 3. Model Components

 •  Loading functions for various land
   uses/land activities
 •  Irrigation return flows
 •  Atmospheric inputs
 •  Pesticides in runoff and sediment

4  Method/Techniques

Loading functions estimate pollutant
loadings for screening applications and
comparison purposes  A generic loading
function is of the following form
= a
                  X0'Cs}' fir,
where
   Le, =
   Xe
   Cs,
   Er, =
pollutant load in sediment
sediment yield
concentration of pollutant i in
soil
enrichment factor for pollutant i
                                       a  = dimensional constant

                                    Additional pollutant load from rainfall may be
                                    accounted for using the following
                                    formulation
                                    where
                                       Lr, =


                                       Qr =
                                       QP =
                                       Cn =
                                       b  =
                                        pollutant load to streams from
                                        rainfall
                                        overland flow
                                        rainfall amount
                                        concentration of pollutant in rainfall
                                        attenuation factor
                                    Runoff can be estimated from the SCS curve
                                    number equation and sediment yield can be
                                    calculated from the USLE   Soil concentra-
                                    tion and enrichment factors can be
                                    determined from field measurement or from
                                    available default values  Several variations
                                    of these forms of loading function can be
                                    used to represent other  pollutant and
                                    pollution sources

                                    5  Applications-

                                    Loading functions have been incorporated
                                    into several hydrologic models to estimate
                                    pollutant loadings  They are also widely
                                    used for screening purposes using desktop
                                    calculators  They can be used to evaluate
                                    atmospheric inputs, urban,  and agricultural
                                    sources including irrigation  return flows,
                                    mining activities, and feedlots
                                                                                  A 1

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6. Number of Pollutants:
11  Simulation Output.
Nitrogen, phosphorus, sediment, heavy
metals, pesticides, organics, salinity

7. Limitations:

•  Accuracy is limited when default
   parameters are substituted for site
   specific data
•  Neglects seasonal variation
•  Can be adapted to predict event or
   seasonal loadings
•  Does not evaluate control practices
   except through assumption of a
   constant removal rate or changes in
   USLE parameters
•  Application can be tedious and time-
   consuming for basins with complex
   multiple land uses and/or pollution
   sources

8. Experience.

EPA Screening Procedures have been
applied (Donigian and Huber,  1991) to
the Sandusky River in Northern Ohio and
the Patuxent, Ware, Chester, and
Occoquan basins in the Chesapeake Bay
region (Davis et al., 1981, Dean et al ,
 1981).

9. Updating Version:

    N/A

 10. Input Data Requirements:

 •  Pollutant concentrations in soils
 •  Enrichment ratios
 •  Nutrient concentrations in
    precipitation
 •  Parameters in the USLE
 •  Land use data
•  Annual pollutant loads (may be adopted
   for seasonal or storm events)
•  Nitrogen inputs to groundwater
•  Salinity in irrigation return flows

12. References Available.

Davis, M J , M K  Snyder, and J W  Nebgen
1981  River basin validation of the water
quality assessment methodology for
screening nondesignated 208 areas -
Volume I: Nonpoint source load estimation
U S  Environmental Protection Agency,
Athens, GA

Dean, J D , B Hudson, and W B Mills
 1981  River basin validation of the MRI
nonpoint calculator and Tetra Tech's
nondesignated 208 screening
methodologies.  Vol. II.  Chesapeake-
 Sandusky nondesignated 208 screening
methodology demonstration U S
 Environmental Protection Agency, Athens,
 Georgia

 McElroy, A D , S W  Chiu, J W  Nabgen, A
 Aleti, and R W  Bennett 1976  Loading
 functions for assessment of water pollution
 for non-point sources. U S  Environmental
 Protection Agency, Washington, DC  EPA
 600/2-76/151 (NTIS PB-253325)

 Mills W B , B B Borcella, M J  Ungs,  S A
 Ghermi, K V  Summers, Mok Lmgsung, G L
 Rupp, G L Bowie, and D A  Haith   1985
 Water quality assessment: A screening
 procedure for toxic and conventional
 pollutants in surface and ground water, Part
 1   US  Environmental Protection Agency,
 Environmental Reaserch Laboratory, Athens,
 GA EPA/600/6-85/002a
A2

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                              The Simple Method
1  Distributor:

Metropolitan Washington Council of
   Governments (MW-COG)
777 North Capitol St , Suite 300
Washington, DC 20002
(202) 962-3200
2  Type of Modeling:

•  Not a computer program
•  Pollutant concentration from urban
   drainage areas
•  Diffuse source
•  Storm-based computations
•  Screening application
3. Model Components-

•  Pollutant export in storm runoff
•  Sediment event mean concentration
   estimates
•  Threshold exceedance frequencies

4  Method/Techniques:

The Simple Method uses the following
expression as its governing equation
where
L, = pollutant loading (Ibs/year)
P = average annual rainfall (inches)
P, = unitless correction factor to account
   for storms that produce no runoff
Rv = runoff coefficient (dimensionless)
C = flow-weighted mean pollutant
     concentration (mg/L)
A =area of development (acres)

Runoff is estimated using runoff coefficients
for the fraction of rainfall converted to
runoff  The portion of storms that do not
produce runoff are accounted for by a
correction factor determined  based on
analyis of site specific or regional
precipitation pattern (p = 0 9 for
Washington, DC area).  Runoff coefficients
are  determined based on the  following
equation
          Rv = 0.05 + 0.009  • PI
where
PI =  percent imperviousness

Pollutant concentrations in runoff depend on
the land use/land activity and can be
obtained from sampling programs such as
the NURP program  Sediment event mean
concentrations are calculated as a function
of the surface area of the drainage basin  It
is assumed that the channels in urban
watersheds are a major source of sediment
and thus larger watersheds will have higher
event mean concentrations Factors such as
the channel stability, storage, and stream
velocity are taken into account in the event
mean concentration determination

5. Applications.

•  Estimate increased  pollutant loading from
   an uncontrolled development site
•  Estimate expected extreme concentration
   that occurs over a specified interval of
   time
                                                                                 A3

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6. Number of Pollutants

Phosphorus, nitrogen, COD, BOD,
metals, including zinc, copper, and lead

7. Limitations:

•  Limited to watersheds where data are
   available or must assume national
   NURP values
•  It is intended for recently stabilized
   suburban watersheds
•  It is limited to small watersheds (less
   than 1 square mile)
•  Application limited to relative
   comparisons

8. Experience:

The Simple Method is used to evaluate
development plans in the metropolitan
Washington, D.C  area

9. Updating Version:

N/A

10. Input Data Requirements:

 •  Characteristics of pollution sources
 •  Flow and concentrations of point
   sources
 •  Areas  served by urban land uses such
   as storm sewers, combined sewers,
   and unsewered areas along with their
   corresponding unit area loads for the
   pollutant of concern
•  Areas and unit area loads for grass and
   woodland areas
•  Parameters for the USLE for croplands
•  Pollutant delivery ratios and pollutant
   reduction efficiency ratio
•  Treatment schemes and associated costs

11  Simulation Output-

•  Total annual loads and load reductions
   achieved by controls for the site or
   watershed
•  Program costs and cost per unit load
   removed

12 References Available

Northern Virginia Planning District
Commission  1981 Comparison of nonpoint
pollution loadings from suburban and
downtown central business districts
Annandale, VA

Northern Virginia Planning District
Commission  1990 Analysis of the
recommended guidance calculation
procedure for the Chesapeake Bay
Preservation Act.  Draft report, Northern
Virginia Planning District Commission.
Annandale, VA

Schueler, T R  1987  Controlling urban
runoff- A practical manual for planning and
designing urban BMPs Metropolitan
Washington Council of Governments
Document  No 87703, Washington, DC
A.4

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                          USGS Regression Method
1  Name of Distributor.

Gary D  Tasker
U S  Geological Survey
430 National Center
Reston, VA 22092

2  Type of Modeling:

•  Not a computer program
•  Pollutant concentration from
   urbanized watersheds
•  Statistical approach
•  Annual, seasonal, or storm event
   mean pollutant loads
•  Screening applications

3  Model Components

•  Regression equations for mean storm
   event pollutant load estimation
•  Confidence interval around the mean

4. Method/Techniques

Regression equations were developed
from historical records of storm loads for
10 pollutants at 76 gaging stations in 20
States  Ten explanatory parameters
were used to reflect possible site
variability associated with pollutant
processes  The nonuniformity of the
variance required a generalized least
squares analysis The general form of
the regression model is as follows
 W =
clA
                          eMJT
                                  „ ~
                           where
                           W =
                           DA =
                           IA =
                           MAR  =
                           Xa =
                           BCF =
         mean storm event pollutant load
         watershed drainage area
         impervious area
         mean annual rainfall
         indicator variable
         bias correction factor
a,b,c,d,e,f = regression coefficients

The mean annual pollutant load can then be
calculated by multiplying W by the mean
annual number of storm events

5  Applications.

•  Estimation of average mean annual storm
   event loads when data are severely
   limited
•  Comparing different locations

6. Number of Pollutants-

Chemical oxygen demand, suspended solids,
dissolved solids, total nitrogen, total
ammonia-nitrogen (NHa-N), total
phosphorus, dissolved phosphorus, total
copper, total lead, and total zinc

7. Limitations

•  Valid only for areas for which regression
   coefficients are provided, i e , regional
   transferabihty is severely limited
•  Valid only within the range of observed
   values of pollutant loads and explanatory
   variables
•  Tends to  underestimate the contributions
   of snowmelt or extreme  events
•  Does not address causation
•  Applies only to small watersheds
                                                                                 A 5

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8. Experience:                              11. Simulation Output.

Limited                                     •  Average annual storm event load and
                                              confidence interval
9. Updating Version:
                                           12 References Available:
   N/A
                                           Tasker, G D , and N E Driver  1988
10. Input Data Requirements:                 Nationwide regression models for predicting
                                           urban runoff water quality at unmonitored
•  Drainage areas                           sites  Water Resources Bulletin 24(5) 1091-
•  Percent imperviousness                   1101
•  Mean annual rainfall
•  Land use indicator
•  Mean minimum January temperature
•  Mean annual number of storm events
A6

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       Sediment and Phosphorus Prediction  (SLOSS, PHOSPH)
1. Name of Distributor.

   N/A (see reference below)

2 Type of Modeling

•  Not a computer program
•  Sediment yield and phosphorus
   loading from a watershed
•  Annual simulation (may be adopted to
   storm events)
•  It is used in combination with GIS
   capabilities
•  Screening  application

3. Model Components

•  Two simple models for sediments and
   phosphorus

4 Method/Techniques

SLOSS uses the Universal Soil Loss
Equation (USLE) to predict erosion and a
sediment delivery ratio is used to
estimate the sediment yreld  Phosphorus
loading is calculated as the product of
the average phosphorus content of the
surface soil and a phosphorus enrichment
ratio  The unique feature of this
approach is not the manner in which the
pollutant loads are calculated but the
ability to integrate simple algorithms with
the Virginia Geographic Information
System (VirGIS), which greatly facilitates
parameter input.
5  Applications:

•  Identify critical areas of pollutant
   production in watersheds
•  Predict annual soil loss and phosphorus
   yields

6. Number of Pollutants1

•  SLOSS predicts erosion and sediment
   yield
•  PHOSPH predicts phosphorus loading

7  Limitations:

•  Does not address seasonal variation
•  Considers sediment and phosphorus only
•  Requires access to GIS data

8  Experience:

   Applied to Nommi Creek watershed in
   Westmoreland County, Virginia

9. Updating Version:

   N/A

10. Input Data  Requirements

•   Parameters for the USLE (soil erodibihty,
   cropping and management factors,
   topography, and rainfall erosivity factor)
   and channel parameters
•   Phosphorus  concentration in soil,
   phosphorus  enrichment ratio
                                                                               A7

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11. Simulation Output:

•  Mean annual loads of sediment and
   phosphorus

12. References Available*

Tim, U.S , S. Mostaghimi, V O
Shanholtz, and N  Zhang 1991
Identification of critical nonpomt pollution
source area using geographic information
systems and simulation modeling  In
Proceedings of The American Society of
Agricultural Engineers (ASAE)
International Summer Meeting,
Albuquerque, New Mexico, June 23-26,
1991.
A.8

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                                  Water Screen
 1  Distributor:

   Office of Planning and Zoning
   Anne Arundel County
   Annapolis, MD

 2  Type of Modeling-

 •  Pollutant loading functions
 •  Screening application

 3  Model Components

 •  Apple II computer program
 •  Modified USLE erosion and sediment
   yield
 •  Loading functions for nutrient and
   organic loadings

 4  Method/Techniques

 Loading factors are calculated for
 watersheds with sufficient data and
 applied to similar watersheds  Sediment
 yield is estimated using the modified
 USLE and a delivery ratio  The specific
 forms of the loading functions differ for
 nitrogen and phosphorus Phosphorus
 inputs are based on concentrations in
 eroded material and an enrichment ratio
 Nitrogen inputs include those associated
 with precipitation  The loading function
 formulations are similar to those used in
the EPA Screening Procedures (McElroy
et  al , 1976, and Zison et al  , 1977)
 5 Applications.

 •  Estimation of pollutant loadings
 •  Preplanning  and screening applications

 6. Number of Pollutants:

 Phosphorus, nitrogen, metals, and organics

 7 Limitations

 •  Cannot assess seasonal variability
 •  Limited to watersheds where data are
   available to calculate loading functions
 •  Limited documentation and applications

 8  Experience

 Water Screen has been applied on the
 Church Creek watershed south of Annapolis,
 Maryland, where it showed discrepancy
 between predictions of the MUSLE and the
 loading functions   Either the loading
functions for  nitrogen and  phosphorus or the
factors used to  estimate nitrogen and
phosphorus concentrations in erosion
predicted by the MUSLE were inappropriate
for this watershed

9  Updating Version.

   N/A

10 Input Data Requirements

 •  Parameters for the MUSLE including the
   rainfall factor (R) for all subwatersheds
   and land uses
 •  Sediment delivery  ratios
                                                                                  A 9

-------
•   Nitrogen, phosphorus, and organic
   matter contents of eroded soils and
   enrichment ratios
•   Atmospheric depositions
•   Loading factors as a function of land
   use

11. Simulation  Output

•   Sediment, total nitrogen, total
   phosphorus, and organic (BOD and
   COD) yield for each land use

12. References Available:

Bird, B.L , and  K M  Conaway  1985
WATER SCREEN - A microcomputer
program for estimating nutrient and
 pollutant loadings In Proceedings of the
Stormwater and Water Quality Model Users
Group Meeting, April 12-13, 1984  ed  by
TOBarnwell  pp 121-174  EPA-600/9-85-
0013

McElroy, A D , D S Chiu, J W Nebgen, A
Aleti, and F W Bennett 1976 Loading
functions for assessment of water pollution
from nonpoint sources.   U S  Environmental
Protection Agency, Washington, DC  EPA-
600/2-76-151

Zison, S W , K F Haven, and W.B  Mills
1977 Water quality assessment - A
screening method for nondesignated 208
areas   U  S  Environmental Protection
Agency, Athens, GA  EPA600/9-77-023
A.10

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                                  WATERSHED
1. Distributor.

John F  Walker
U S Geological Survey
6417 Normandy Lane
Madison, Wl 53719-1133
(608) 274-3535

2. Type of Modeling:

•  Various multiple point sources plus
   continuous and diffuse source/release
•  Screening application

3  Mode! Components-

•  Program is divided into seven
   worksheets.  The first summarizes
   basic watershed characteristics
   The next three worksheets estimate
   pollutant loads from point sources and
   cropland and non-cropland agricultural
   land  uses for controlled and
   uncontrolled conditions.  Sources are
   totaled for controlled and uncontrolled
   conditions by worksheet 5
•  Program costs and cost-effectiveness
   per unit load reduction are also
   calculated

4  Method/Techniques

Separate methods are used to calculate
urban, rural non-cropland, and rural
cropland loads  Urban loads are
calculated from point estimates of flow
and concentration, rural non-cropland
loads are estimated on a unit area basis,
and rural cropland loads are based on the
Universal Soil Loss Equation (USLE)  The
rainfall factor (R) in the USLE is
 unspecified for use as a calibration
 parameter  Delivery ratios and trapping
 efficiencies for tributary wetlands are used
 to convert  eroded sediment to sediment
 delivered   These values are also calibrated
 The model  used the sorting features of the
 EXCEL® spreadsheet program for the
 Macintosh  computer to rank the most cost-
 effective alternatives

 5  Applications:

 •  Phosphorus loading from point sources,
   CSOs, septic tanks, rural cropland,  and
   non-cropland rural sources was estimated
   for Delavan Lake watershed  in
   Wisconsin
 •  Evaluation of the trade-offs between
   control of point and nonpomt sources

 6  Number  of Pollutants:

 Used for only one at a time, e g  phosphorus

 7  Limitations:

 •  Cannot  assess seasonal variability
 •  Can assess only a limited number of land
   management control practices
 •  Requires calibration to determine the
   rainfall factor and the sediment delivery
   ratio
 •  Can assess only contaminants  associated
   with soils and sediments

8. Experience:

Watershed  was applied to the study of point
and nonpomt sources in the Delavan Lake
watershed in Wisconsin  It was determined
that runoff  controls would be insufficient to
                                                                                 A 11

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meet water quality standards  Instead of
focusing controls for phosphorus on
nonpomt sources, the study
recommended several in-lake controls

9. Updating Version

   N/A

10. Input Data Requirements:

•  Sources of pollution along with their
   respective position and point of entry
   to the basin
•  Flows and concentrations of point
   sources
•  Areas served by urban land uses such
   as storm sewers, combined sewers,
   and unsewered areas along with their
   corresponding unit area loads for the
   pollutant of concern
•  Areas and unit area  loads for grass
   and woodland areas
•   Parameters for the USLE for croplands
•   Pollutant delivery ratios and pollutant
   reduction efficiency ratio
•   Treatment schemes and associated costs

11. Simulation  Output.

•   Total annual loads and load reductions
   achieved by controls for the site or
   watershed
•   Program costs and cost per unit load
   removed

12  References Available-

Walker, J  F , S  A Pickard, and W C
Sonzogni  1989  Spreadsheet watershed
modeling for nonpomt-source pollution
management in a Wisconsin basin  Water
Resources Bulletin 25(1) 139-147
A 12

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          FHWA:  The Federal Highway Administration Model
1. Distributor.

Office of Engineering and Highway
   Operations R&D
Federal Highway Administration
6300 Georgetown Pike
McLean,  VA 22101

2  Type of Modeling

-  Statistical
•  Screening application

3  Model Components

•  Computation of water quality impact
   from site data for either lakes or
   streams
•  Simple evaluation of controls

4  Method/Techniques.

Pollutant  loadings and the variability of
loadings are estimated from runoff
volume distributions and event mean
concentrations for the median runoff
event at a site.  Rainfall is converted to
runoff using a runoff coefficient
calculated from the percent
imperviousness  Runoff velocity is
estimated from runoff intensity.  Mean
runoff concentrations are calculated from
site median pollutant concentrations,
coefficient of variation for event mean
concentrations (EMCs), and the mean
EMC as
      MCR = TCR •  Vd+CVC/?2)
where
MCR=   mean EMC for site (mg/L)
TCR=   site median pollutant concentration
         (mg/L)
CVCR =  coefficient of variation of EMCs

Mean event mass loading is computed as

    M(Mass) = MCR-MVR- (62 45 • 10'6}
where
M(Mass) =  mean pollutant mass loading
         (pounds per event)
MCR=   mean runoff concentration (mg/L)
MVR =   mean storm event runoff volume
         (cf)

Annual loads are calculated by multiplying
by the number of storms per year  Pollutant
build-up is based on traffic volumes  and
surrounding area characteristics

5 Applications

•  Evaluation of lake and stream impacts of
   highway stormwater discharges
•  Uncertainty analysis of runoff and
   pollutant concentrations, or loads
•  Highway stormwater runoff management

6 Number of Pollutants.

Heavy metals (copper, lead, and zinc),
nitrogen, and phosphorus

7 Limitations:

•  Assesses seasonal variability in a limited
   manner as expressed in the probability
   distributions of the output
•  Limited in its evaluation of controls
                                                                               A 13

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•  Does not consider the soluble fraction
   of pollutants or the precipitation and
   settling of phosphorus in lakes

8. Experience:

The FHWA model was used by the
Federal Highway Administration to
evaluate the impacts of stormwater
runoff from highways and their
surrounding drainage areas

9. Updating Version:

   N/A

10. Input Data Requirements-

 •  Hourly rainfall data to be transformed
   into mean and coefficient of variation
 •  Drainage and paved areas, average
   rainfall volumes, intensities, and
   durations
 •  Coefficients of variation are required
   for all average rainfall characteristics
 •  Traffic volumes for the surrounding
   area are required
 •  Runoff concentrations (average and
   coefficient of variations) for each
   pollutant
11  Simulation Output

•  Mean and variance of m-stream or lake
   concentrations
•  Mean and variance of pollutant loadings
   and concentrations in runoff

12  References Available

Dnscoll, E D , P E Shelley, and E W
Strecker 1990  Pollutant loadings and
impacts from highway stormwater runoff.
Volume I.  Design procedure  Prepared for
the Office of Engineering and Highway
Operations R&D, Federal Highway
Administration

Dnscoll, E D , P E Shelley and E W
Strecker 1990 Pollutant loadings and
impacts from highway stormwater runoff.
Volume II. Users guide for interactive
computer implementation of design
procedure  Prepared for the Office of
Engineering and Highway Operations R&D,
Federal Highway Administration
A.14

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                  I/I/MM/ Watershed Management Model
 1  Distributor:

 Prepared by Camp Dresser & McKee Inc
 for Stormwater Management Division,
 Florida Department of Environmental
 Regulation
 Twin Towers Office Building
 2600 Blair Stone Road
 Tallahassee, Florida  32301-8241
 (904) 488-6221

 2. Type of Modeling:

 •  Watershed Stormwater pollutant loads
 •  Multiple diffuse source release
 •  Annual time steps
 •  Screening application

 3. Model Components

 •  Computation of annual nutrient and
   metal loads to  reservoirs
 •  Computation of m-lake or m-stream
   water quality from  pollutant loads
 •  Load reduction estimates for site or
   regional BMP implementation
 •  Uptake and removal in stream courses
 •  Estimates of annual pollutant loads
   from baseflow
 •  Comparison with point sources
 •  Failing septic tank loads
 •  Chlorophyll-a and nutrient
   concentrations in downstream lakes
   and reservoirs

4. Method/Techniques.

 Runoff coefficients are used for rural
areas, for urban areas  runoff is based on
a linear function of the percent
imperviousness Loading  of nutrients and
metals is based on event mean
concentrations measured locally or from
NURP data  Baseflow is estimated from
flow records and concentrations  There is a
choice of three lake water quality routines
that output mean annual concentrations of
chlorophyll-a. (The model can be adapted to
predict seasonal loads or chlorophyll-a
concentrations provided that seasonal event
mean concentration data are available )
Simple calculations are included for m-
stream transport and transformation based
on travel time  The program can assess the
relative contributions of point and nonpomt
sources  Resultant water quality is
predicted with a version of the Vollenweider
eutrophication model, adapted to lakes in
the southeastern United States  Removal  of
metals associated with sediments in
reservoirs  is estimated from the sediment-
trapping efficiency of the reservoir

5  Applications:

Estimates  the annual nonpomt source loads,
including baseflow and precipitation inputs,
for management planning

6. Number of Pollutants

Total phosphorus, total nitrogen, lead, and
zinc

7. Limitations

•  Accuracy is limited when default
   parameters are substituted for site-
   specific data
•  Neglects seasonal variation
•  Does not predict sediment yields
                                                                                A 15

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•  Does not evaluate control practices
   except through assumption of a
   constant removal fraction
•  Does not consider loadings associated
   with snowmelt events
•  Can assess only  relative impacts of
   land use categories or controls

8. Experience:

The model has been applied to between
10 and 15 watersheds   It has been used
as part of a wasteload allocation study
for Lake Tohopekaliga and for
Jacksonville, Florida, watershed's Master
Plan.  It has been applied in Norfolk
County, Virginia, and to a Watershed
Management Plan for North Carolina

9. Updating Version

Under development

10. Input Data Requirements

 •  Land use and soil types
 •  Average annual precipitation,
   evaporation, and evapotranspiration
 •  Nutrient concentrations in
   precipitation
•   Annual baseflow and baseflow pollutant
   concentrations
•   Event mean concentrations in runoff
•   Reservoir, lake, or stream hydraulic
   characteristics
•   Removal efficiencies of proposed BMPs

11  Simulation Output

•   Annual pollutant loads from point and
   nonpomt  sources, including both
   agricultural and  urban land use
•   Relative magnitude of inputs from point
   sources and septic tanks
•   Load reductions from combined effects
   of multiple BMPs
•   In-lake nutrient concentrations as related
   to trophic state, also, concentrations of
   metals are evaluated for the reservoir
•   Standard  statistics and bar graphs of
   results

12. References Available

Camp, Dresser and McKee (COM)  1992
Watershed Management Model user's
manual. Version  2 0  Prepared for the Florida
Department  of Environmental Regulation,
Tallahassee, FL
A16

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                 NPSMAP: Nonpoint Pollution Source Model for
                              Analysis and Planning
1  Distributor

Dr  Jack Douglas Smith
Project Manager
Water Resources/Quality
Fetrow Engineering, Inc
12300 S E Mallard Way, Suite 205
Milwaukee, OR 97222
(503) 652-1526

2  Type of Modeling

•  Multiple land use watersheds
•  Water quality analysis
•  Continuous simulation (hourly data,
   one year at a time)
•  Point and nonpomt sources
•  Wasteload and load allocations
•  Screening application

3. Model Components:

•  Runoff and pollutant loading
   assessment
•  Water quality and resources
   management analysis
•  Simulation of wet detention or
   wetland system controls for each
   subbasm or stream segment
•  Irrigation and drainage
•  Snowfall and snowmelt
•  Uses Lotus 1-2-3® spreadsheet

4. Method/Techniques

NPSMAP is a spreadsheet-based program
that operates within the Lotus 1-2-3®
programming environment  NPSMAP is a
dynamic simulation program that includes
three primary computation modules
(SIMULATE, ALLOCATE, and
PROBABILITY). SIMULATE computes daily
runoff, pollutant loadings, streamflow, and
water quality ALLOCATE simulates stream
segment load capacities (LCs), point source
wasteload allocations (WLAs), and nonpomt
source load allocations (LAs)  PROBABILITY
computes the probability distributions of
runoff and loadings

5  Applications

•  Nonpoint source runoff and pollutant
   (nutrient) loadings, including surface
   water storage in reservoirs and wetlands
•  Point source discharges and streamflow
•  Groundwater levels, irrigation and other
   water uses, and water quality

6  Number of Pollutants*

Nitrogen and phosphorus

7  Limitations.

•  No sediment is evaluated
•  Limit on simulation period  (one year at a
   time)

8  Experience

Applied to the Tualatin River basin for
Oregon Department of Environmental Quality

9  Updating Version

Version 1 0 (1990)
                                                                               A 17

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10. Input Data Requirements.

•  Hydrology data stream segment
   volumes and streamflow recession
   coefficients, parameters for upland
   groundwater, parameters and
   exchange matrix for valley fill
   groundwater model, and rainfall
   intensity
•  Land use data land use distributions
   and parameter values in each stream
   segment, soil parameters, and SCS
   curve number and retention
   coefficients
•  Weather  records including rainfall,
   snowfall, temperature, and
   evapotranspiration

11. Simulation Output

•  Daily runoff and streamflow
•  Nonpomt source runoff and loads
•   Treatment plant discharges, loadings,
   overflows/bypasses
•   Groundwater, streamflow, and water
   quality (loads and concentrations)
•   Bar graphs, two- and three-dimensional
   graphs are available for simulation results
•   Statistical summary
•   Probability distributions of runoff and
   loadings
•   Stream segment load capacities (LCs),
   point source wasteload allocations
   (WLAs), and nonpomt source load
   allocations(LAs)

12 References Available

Omicron Associates  1990 Nonpomt
Pollution  Source Model for Analysis and
Planning  (NPSMAP) - Users manual
Omicron Associates, 11265 NW Rammont
Road, Portland, OR
A.18

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           GWLF: Generalized Watershed Loading Functions
1  Distributor

Dr Douglas A  Haith
Department of Agricultural and
   Biological Engineering
Cornell University
Ithaca, NY 14853
(607) 255-2802

2  Type of Modeling

•  Pollutant loads from urban and
   agricultural  watersheds
•  Continuous simulation  using daily time
   step
•  Point and nonpomt sources
•  Screening to intermediate application
•  Evaluation of effects of land use
   changes

3  Model Components:

•  Rainfall/runoff assessment
•  Surface water/groundwater quality
   analysis

4. Method/Techniques

This  model is based on simple runoff,
sediment, and  groundwater relationships
combined with empirical chemical
parameters.  It evaluates streamflow,
nutrients, soil erosion, and sediment yield
values from complex watersheds   Runoff
is calculated by means of  the SCS  curve
number equation  The Universal Soil
Loss Equation  (USLE) is applied to
simulate erosion   Urban nutrient loads
are computed by exponential wash-off
functions. Groundwater runoff and
discharge are obtained from a lumped-
parameter watershed water balance for both
shallow saturated and unsaturated zones
Calibration is not required for water quality
data

5. Applications:

Relatively large watersheds with multiple
land uses and point sources

6. Number of Pollutants:

Total and dissolved nutrients  (nitrogen and
phosphorus) and sediment

7. Limitations:

•  Simulation of peak nutrient fluxes is
   weak
•  Stormwater storage and treatment are
   not considered

8 Experience:

GWLF was validated for an 85,000-hectare
watershed from the West Branch Delaware
River Basin in New York using a 3-year
period of record

9. Updating Version

Under development

10. Input Data Requirements.

•  Daily precipitation and temperature data
   and runoff source areas
•  Transport parameters'  runoff curve
   numbers, soil loss factor,
   evapotranspiration cover coefficient,
   erosion product, groundwater recession
                                                                               A 19

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   and seepage coefficients, and
   sediment delivery ratio
 •  Chemical parameters  urban nutrient
   accumulation rates, dissolved nutrient
   concentrations in runoff, and solid-
   phase nutrient concentrations in
   sediment
 •  Point sources

 11. Simulation  Output-

 •  Annual and  seasonal runoff,
   streamflow, watershed erosion, and
   sediment yield
 •  Annual and  seasonal total and
   dissolved nitrogen and phophorus
   loads in streamflow and groundwater
   discharge to streamflow
 •  Annual erosion and total/dissolved
   nitrogen and phosphorus loads from
   each land use
 •  Annual and  seasonal pollutant
   loadings by  land use type and
   pollution sources

 12. References Available

 Brown, M P., M.R Rafferty, and P
 Longabucco. 1985   Nonpoint source
 control of phosphorus - A watershed
 evaluation. Report to the U S
 Environmental Protection Agency, Ada,
 OK.
Delwiche, L L D  and D A Haith. 1983
Loading functions for predicting nutrient
losses from complex watersheds  Water
Resources Bulletin 19(6) 951-959

Haith, D A 1985 An event-based procedure
for estimating monthly sediment yields
Transactions of the American Society of
Agricultural Engineers 28(6) 1916-1920

Haith, D A and L L  Shoemaker  1987
Generalized watershed loading functions for
stream flow nutrients  Water Resources
Bulletin 23(3) 471-478

Haith, D A andLJ Tubbs 1981
Watershed loading functions for nonpomt
sources Proceedings of the American
Society of Civil Engineers Journal of the
Environmental Engineering Division
107(EE1)  121-137

Wu, S  R , D A  Haith, and J H Martin, Jr
1989  GWLF - Generalized Watershed
Loading Functions - User's manual.
Department of Agricultural Engineering,
Cornell  University, Ithaca, NY
A.20

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                    P8-UCM:  Urban Catchment Model
1 Distributor

Narragansett Bay Project
291 Promenade Street
Providence, Rl 02908-5767
(401)  521-4230

2. Type of Modeling

•  Urban watersheds
•  Storm event/sequence simulation
•  Surface water quality analysis
•  Evaluation of BMPs and development
   of  design criteria
•  Single, continuous, and diffuse
   source/release
•  Screening application

3 Model Components:

•  Rainfall, stormwater runoff
   assessment
•  Surface water quality analysis
•  Routing through structural controls

4 Method/Techniques

The P8 program predicts the generation
and transport of stormwater runoff
pollutants in small urban catchments  It
consists mainly of methods derived from
other  tested urban runoff models (i e ,
SWMM, HSPF, D3RM, TR-20).  Runoff
from impervious areas is calculated
directly from rainfall once depression
storage is exceeded  Particle build-up
and wash-off processes are obtained
using  equations derived primarily from
the SWMM program  The SCS curve
number equation is used to  predict runoff
from pervious areas  Water balance
calculates percolation from the pervious
areas  Baseflow is simulated by a linear
reservoir  Without calibration, use of model
results should be limited to relative
comparisons

5 Applications

•  Surface water quantity and quality
   routing
•  Small urban area assessments
•  Watershed-scale land use planning
•  Site planning and evaluation for
   compliance
•  Selecting and sizing BMPs

6. Number of Pollutants*

Ten pollutants, including total suspended
solids (TSS), total phosphorus, total Kjeldahl
nitrogen, lead, copper, zinc, and
hydrocarbons

7 Limitations.

•  No snowfall, snowmelt, or erosion is
   calculated
•  Effects of variations in vegetation type/
   cover on evapotranspiration are not
   considered
•  Watershed lag is not simulated

8 Experience:

   N/A

9. Updating Version

Version 1  1 (1990)
                                                                                A 21

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 10. Input Data Requirements.

 •  Device (hydraulic) parameters for
   pond, basin, buffer, pipe, splitter, and
   aquifer
 •  Watershed parameters areas,
   impervious fraction and depression
   storage, street-sweeping frequency,
   SCS runoff curve number for pervious
   portion
 •  Particle parameters
   accumulation/wash-off parameters,
   runoff concentrations, street-sweeper
   efficiencies, settling velocities, decay
   rates, filtration efficiencies
 •  Water quality component parameters
   pollutant concentrations
 •  Air temperatures required for stream
   baseflow computations

 11. Simulation Output:

 •  Water and mass balances, removal
   efficiencies, mean inflow/outflow
   concentrations, and statistical summaries
   by device and component
•  Comparison of flow, loads, and
   concentration across devices
•  Peak elevation and outflow ranges for
   each device
•  Sediment accumulation rates by device
•  Violation frequencies for event mean
   concentrations

12. References Available

Palmstrom, N , and W W  Walker, Jr  1990
P8 Urban Catchment Model: User's guide,
program documentation, and evaluation of
existing models, design concepts, and Hunt-
Potowomut data inventory. The
Narragansett Bay Project Report No  NBP-
90-50
A.22

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             SIMPTM:  Simplified Particle Transport Model
 1. Distributor-

 Roger C  Sutherland
 Software Distribution
 OTAK, Inc
 17355 Boones Ferry Road
 Lake Oswego, OR 97035
 (503) 635-3618
 Cost:  §495

 2  Type of Modeling.

 •  Stormwater from urban watersheds
 •  Storm event/sequence simulation
 •  Continuous and diffuse source release
 •  Screening applications
 •  Evaluation of BMPs

 3  Model Components.

 •  Rainfall/runoff assessment
 •  Surface water quality analysis

 4  Method/Techniques

 SIMPTM simulates the accumulation,
 wash-off, and mechanical removal of up
 to six different pollutants contained in
 total solids or particulate matter
 accumulating on paved areas that are
 directly connected to storm dram
 systems  Runoff is calculated using
 runoff thresholds and originates only
 from paved areas directly connected to
 storm dram systems  SIMPTM converts
 event trapezoidal hyetographs into
trapezoidal hydrographs using the runoff
duration and small storm impervious area
 loss equations developed by Pitt (1987)
Street cleaning, catchbasm accumulation,
and on-site retention are expressed as a
 function of particle size distribution
 Simulation of runoff or pollutant loads from
 pervious areas and baseflow is ignored

 5 Applications:

 •  Simulation of runoff and sediment yields
   from urban watersheds with small,
   storm-based hydrology
 •  Effectiveness of various, primarily
   nonstructural controls, such as street and
   catchment cleaning

 6. Number of Pollutants

 Six pollutants including sediment
 components, nitrogen, phosphorus, chemical
 oxygen demand

 7  Limitations:

 •  Snow accumulation and snowmelt are
   ignored in the hydrology simulation
 •  Nutrient transformations are not
   evaluated
 •  Runoff and  pollutants are assumed to
   originate  solely from impervious areas
   directly connected to the drainage
   system
 •  Model testing in Pacific Northwest only

8  Experience.

The model was calibrated using National
Urban Runoff Program (NURP) data from the
Lake Hills  basin in Bellevue, Washington
Subsequently, the model was tested using
NURP data for the Surrey Downs basin, also
in the Bellevue area  The simulation of
variability  of runoff events was excellent
considering the simplistic approach used to
                                                                               A 23

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convert rainfall into runoff volumes  The
predicted variability in pollutant loads
was less variable than was actually
observed.

Version 1  (1980) was applied to over
57,000 acres of urban and urbanizing
land surrounding Reno, Nevada, for the
Washoe County Council of Governments
for the purpose of comprehensive
stormwater management

9. Updating Version:

Version 2  1 November 1990

10. Input  Data  Requirements:

•   Rainfall depths for 1-, 3-, or 6-hour
    periods
•   Pollutant strengths and accumulation
    and wash-off parameters
•   Particle size distributions
•   Curb lengths and  characterization of
    impervious surfaces

11. Simulation  Output-

•   Runoff volumes, durations, pollutant
    loadings, and event mean
    concentrations for each rainfall event
•   Results may be reported for each
    subcatchment or  for the entire
    watershed
•  Although graphic output is not available,
   results can be imported to spreadsheets,
   such as Lotus 1-2-3®
•  Average monthly and annual statistics
   are calculated for rainfall depths,
   durations, and intensities

12 References Available:

Pitt, R E  1987 Small storm urban flow and
particulate wash-off contributions to outfall
discharges Ph D Dissertation, Civil and
Environmental Engineering Department,
University of Wisconsin, Madison, November
1987

Sutherland, R C , D L  Green, and S L  Jelen
1990 Simplified Particulate Transport
Model, Users manual  OTAK, Inc Lake
Oswego, Oregon

Sutherland, R C 1991   Modeling  of urban
runoff quality in Bellevue, Washington using
SIMPTM  In Proceedings from the  technical
sessions of the regional conference on
nonpoint source pollution: The unfinished
agenda for the protection of our water
quality, March 20-21, 1991, Tacoma, WA
Published by the State of Washington Water
Research Center
A.24

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                    Automated Q-ILLUDAS  (AUTO-QI)
 1  Distributor.

 Michael L  Terstnep
 Illinois State Water Survey
 2204 Griffith Drive
 Champaign, Illinois 61820-7495
 Cost  $50

 2  Type of Modeling

 •  Urban stormwater processes
 •  Storm event simulation
 •  Continuous and diffuse pollutant
   sources
 •  Screening and intermediate
   applications
 •  Evaluation of BMPs

 3  Model Components

 •  Rainfall/runoff assessment from
   pervious and impervious areas
 •  Water quality analysis (emphasis on
   nutrients and sediments)
 •  Simulation of BMPs, separate or
   overlapping
 •  Linkage to geographic information
   system  (GIS)

4  Method/Techniques

AUTO-QI is based on continuous
simulation of soil moisture  Runoff
volumes are adjusted for soil moisture,
pervious and impervious depression
storage, interception, and infiltration
based on Morton infiltration curves
Exponential pollutant accumulation and
wash-off functions are used to determine
the pollutant loads  The impacts of a
 series of pollutant reduction practices are
 simulated based on user-supplied removal
 efficiencies

 5 Applications-

 •  Simulation of runoff volumes, pollutant
   loads, and event mean concentrations
 •  Comparison of pollutant levels with and
   without BMPs and with various fertilizer
   application rates

 6 Number of Pollutants.

 Several pollutants including nitrogen,
 phosphorus, chemical oxygen demand
 (COD), metals,  and bacteria (at least three at
 once)

 7  Limitations-

 •  Does not calculate pollutant removal
   efficiencies, removal efficiencies  must be
   supplied by the user
 •  Lacks nutrient transformation and
   mstream processes
 •  Tested in the State of Illinois only
 •  No simulation of subsurface soil
   processes

8. Experience

Simulation of urban pollutant loads for
suspended solids, phosphorus, and lead
from the greater Lake Calumet area after
calibration on Boneyard Creek in Champaign,
Illinois (1990)
                                                                                A 25

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9. Updating Version:

October 1990

10. Input Data Requirements-

•  Daily and hourly rainfall data
•  Monthly evaporation and
   evapotranspiration values
•  BMP removal efficiencies
•  Soil infiltration parameters
•  Land use parameters and  soil types
   for each subcatchment
•  Build-up and wash-off characteristics
   of each pollutant

11. Simulation Output:

•  A summary for the watershed by
   event is created for rainfall, runoff,
   and runoff duration
•  Event mean concentrations and
   loadings
12. References Available.

Terstnep, M. L , M T  Lee, E  P Mills, A V
Greene, and M R. Rahman  1990
Simulation of urban runoff and pollutant
loading from the Greater Lake Calumet area
Prepared by the Illinois State Water Survey
for the U S Environmental Protection
Agency, Region V, Water Division,
Watershed  Management Unit,  Chicago, IL
A 26

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        AGNPS: Agricultural Nonpoint Source Pollution Model
1  Distributor

Basil Meyer
North Central Soil
Conservation Research Laboratory
U S  Dept  of Agriculture
Agricultural Research Service
Morris, MN 56267
(612) 589-3411

2  Type of Modeling

•  Simulation of pollutant loads from
   agricultural watersheds
•  Storm-event simulation
•  Point source/release
•  Distributed modeling using a grid
   system with square elements
•  Screening, intermediate, and detailed
   applications
•  Evaluation of BMPs

3  Model Components

•  Rainfall/runoff assessment
•  Water quality analysis (emphasis on
   nutrients and sediments)
•  Point source inputs available (feedlots,
   springs, wastewater treatment plant
   discharge, bank and gully erosion)
•  Unsaturated/saturated zone routines
•  Economic analysis
•  Linkage to CIS possible

4  Method/Techniques

This model can identify critical areas of
sediment and nutrient production in a
watershed and can assess the impacts of
best management practices (BMPs). Soil
erosion is simulated by the modified
Universal Soil Loss Equation (USLE)  The
unit hydrograph approach is used to predict
water flow, while the SCS curve number
equation is applied to estimate runoff
volume Some versions are linked to GIS
and DEM with automatic generation of
terrain parameters (Panuska et al , 1991)

5  Applications

•  Erosion, sediment, and chemical
   transport
•  Surface water flow routing

6  Number of Pollutants

Four pollutants nitrogen, phosphorus,
chemical oxygen demand (COD), and
sediment

7  Limitations

•  Only single event version is currently
   available, although a continuous
   simulation version (ANNAGNPS) should
   be released soon
•  Does not handle pesticides
•  Lacks nutrient transformation and
   mstream processes
•  Needs further field testing for pollutant
   transport component
•  No simulation of subsurface soil
   processes
•  Rainfall intensity is not considered in the
   runoff analysis

8.  Experience.

•  Economic assessment of soil erosion and
   water quality in Idaho (1987)
                                                                                A 27

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•  Economic effect of nonpomt pollution
   control alternatives (1988)
•  Analysis of agricultural nonpomt
   pollution control options in St  Albans
   Bay, Vermont (1987)
•  Water quality evaluation of Garvm
   Brook watershed (1989)
•  Alternative management practices in
   Salmonson Creek watershed (1989)
•  Applied along with a GIS to the Owl
   Run watershed, which is part of the
   Chesapeake  Bay watershed, to predict
   the effectiveness of BMP  installation

9. Updating Version

Single event AGNPS Version 3 65
Soon to be released are AGNPS Version
4 0 (written in C)  and continuous
simulation AGNPS (ANNAGNPS)

10. Input Data Requirements

•  Topography  and soil characteristics
•  Meteorologic data
.  Land use data  (cropping history and
   nutrient applications)
•  Point source data

11. Simulation Output

 •  Hydrology output storm runoff
   volume and  peak rate
 •  Sediment  output sediment yield,
   concentration, particle size
   distribution,  upland erosion, amount
   of deposition
 .  Chemical output  pollutant
   concentration  and load

 12. References Available

 Frevert, K and  B M  Crowder 1987
Analysis of agriculture nonpoint pollution
 control options in the St. Albans  Bay
watershed  Economic Division, ERS, USDA,
Staff Report No AGES870423

Hewitt, M J 1991  GIS for nonpoint source
watershed modeling applications In EPA
Workshop on the Water Quality-based
Approach for Point Source and Nonpoint
Source Controls, June 1991, p  34
EPA503/9-92-001

Kozloff, K , S J Taff, and W Wang  1992
Microtargetmg the acquistion of cropping
rights to  reduce nonpoint source water
po 11 utio n  Wa ter Resources Research
28(3) 623-628

Lee, M T 1987 Verification and
applications of a nonpoint source pollution
model  In Proceedings of the National
Engineering Hydrology Symposium,  ASCE,
New York,  NY

Panuska, J C , I D  Moore, and  L A  Kramer
1991 Terrain analysis  Integration into the
agricultural nonpoint source (AGNPS)
pollution model Journal of Soil and Water
Conservation 46(1) 59-64

Prato, T  , H Shi, R  Rhew, and M  Brusven
1989 Soil  erosion and nonpomt-source
pollution control in an Idaho watershed
Journal of Soil Water Conservation
44(4) 323-328

Setia, P P , R S Magleby, R S , and D G
Carvey   1988  Illinois rural clean water
project - An economic analysis Resources
and Technology Division,  ERS,  USDA  Staff
Report No  AGES830617

Young, R A , C A  Onstad, D D Bosch, and
W P Anderson 1986 Agricultural Nonpoint
Source Pollution Model A watershed
analysis tool Agriculture  Research Service,
U S Department of Agriculture, Morris, MN
A 28

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           SLAMM: Source Loading and Management Model
1  Distributor

Dr  Robert Pitt
Department of Civil Engineering
University Station
Birmingham, AL
(205) 934-8430

2  Type of Modeling

•  Continuous and diffuse source/release
•  Continuous series of storm events (up
   to 150)
•  Screening application
•  Evaluation of controls

3  Model Components

•  Rainfall/runoff assessment
•  Water quality analysis

4  Method/Techniques.

This program can evaluate the effects of
a number of different stormwater control
practices on runoff routines  SLAMM
performs continuous mass balances for
particulate and dissolved pollutants and
runoff volumes   Runoff is calculated by
a method developed by Pitt (1987) for
small storm hydrology  Runoff is based
on infiltration minus initial abstraction
and is calculated for both pervious and
impervious areas  Triangular
hydrography is used to simulate the
hydrology  A statistical approach is used
to parametrize the hydrographs
Exponential build-up and wash-off
functions are  used for pollutant loading,
which is assumed to come from
impervious areas  Loading from pervious
areas is constant concentration supplied by
user  Water and sediment from various
source areas is tracked by source area as it
is routed through various treatment devices
The program considers how particulates
filter or settle out in control devices
Particulate removal is calculated based on
the design characteristics of the basin or
other removal device  Storage and overflow
of devices is also considered  At the outfall
locations, the characteristics of the source
areas are used to determine pollutant loads
in solid and dissolved phases   Loads from
various source areas are summed

5 Applications

•  Evaluates multiple control strategies such
   as wet detention basins, porous
   pavement, infiltration devices, street
   cleaning, catchment cleaning, grass
   swales, roof runoff disconnections, and
   paved parking lot disconnections
•  Planning tool  for urban runoff quality and
   quantity assessments
•  Applicable to  the study of stormwater
   pollutant control from regions frequently
   receiving rainfall events of less than  1
   inch

6. Number of Pollutants

Particulate and dissolved pollutants
(depending on the calibration information),
such as particulate and filterable forms of
residue, phosphorus, phosphate, total
Kjeldahl nitrogen, chemical oxygen demand
(COD), fecal cohform bacteria, aluminum,
copper, lead, and zinc
                                                                                 A 29

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7. Limitations:

•  Does not evaluate snowmelt and
   baseflow conditions
•  Will not provide individual storm
   predictions
•  Evaluates runoff characteristics at the
   source area within the watershed and
   at the discharge outfall but does  not
   consider mstream processes that
   remove or transform pollutants
•  Does not evaluate receiving water
   quality responses
•  Requires between 10 and 100 storms
   in a study period (maximum 150)
•  Does not develop or evaluate specific
   hydraulic designs
•  Does not model  erosion from pervious
   areas or construction sites

8. Experience.

SLAMM has been used in conjunction
with receiving water quality models
(HSPF) to examine the ultimate effects
on urban runoff from Toronto for the
Ontario Ministry of the Environment
SLAMM was also used to evaluate
control  options for controlling  urban
runoff in Madison, Wisconsin, using CIS
information  The State of Wisconsin
uses SLAMM as part of its Priority
Watershed Program It was used in
Portland, Oregon, for a study evaluating
CSOs.

9. Updating Version:

Currently being updated

 10.  Input Data Requirements:

 • Rainfall start and end dates (and
   times) and rainfall depths
 • Areas of each source type, effective
   SCS soil type
•   Building and traffic density
•   Pavement texture, roof pitch, and
   presence of alleys
•   Land use
•   Shape, size, and type of outlet structures
   of the wet detention basin
•   Soil infiltration rates for infiltration
   devices

11  Simulation Output-

•   Source area and outfall flow volume
   estimates for  each rainfall period and land
   use
•   Source area and outfall particulate
   residue mass  discharge and
   concentration estimates for each rainfall
   period and land use
•   Relative source area runoff volume and
   particulate residue mass
   contribution estimates for each rainfall
   period
•   Mass discharge, concentration, and
   relative contribution estimates for  each
   pollutant selected
•   Cost estimates of stormwater control
   practices, graphical summaries,  baseflow
   predictions, and snowmelt predictions are
   under development

12 References

Pitt, R 1979 Demonstration of non-point
pollution abatement through improved street
cleaning practices U S Environmental
Protection Agency, Cincinnati, OH  PA-
600/2-79-161  (NTIS PB80-108988)

Pitt, R 1986 Runoff controls in Wisconsin's
priority watersheds  In  Urban runoff quality,
ed B  Urbonas,  and L A  Roesner,
Proceedings of the Engineering Foundation
Conference on Urban Runoff Quality  (ASCE),
June  22-27, 1986, in Henniker, NH.
A.30

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        STORM: Storage,  Treatment, Overflow, Runoff Model
1. Distributor:

U S  Army Corps of Engineers
The Hydrologic Engineering Center (HEC)
609 Second Street
Davis, CA 95616
Cost. $200 - 9-track magnetic tape

2  Type of Modeling

•  Urban runoff processes
•  Continuous simulation (hourly time
   steps)
•  Continuous and diffuse source/release
•  Screening application

3  Model Components-

•  Rainfall/runoff assessment
•  Water quality analysis
•  Statistical and sensitivity analysis

4  Method/Techniques.

This is a quasi-dynamic program A
modified rational formula is used for
hydrology simulation  Rainfall/runoff
depth and volumes are computed by
means of an area-weighted runoff
coefficient and the SCS curve number
equation, respectively   The  Universal
Soil Loss Equation (USLE) is applied to
simulate erosion  Water quality is
simulated by linear build-up and first-
order exponential wash-off coefficients
Calibration is advisable, but relative
comparisons can be evaluated without
calibration
5. Applications:

•  Storm and combined sewer overflows
   including dry-weather flow
•  Surface water quantity and quality
   routing with storage/treatment option
•  Urban areas assessments

6  Number of Pollutants

Six prespecified pollutants  suspended
solids, settleable solids, BOD, total
cohforms, ortho-phosphate, and total
nitrogen

7. Limitations

•  Little flexibility in parameters to calibrate
   to observed hydrographs
•  Lacks microcomputer version
•  Requires a large amount of input data

8  Experience:

STORM  was extensively used in the late
1970s and early 1980s.  The model was
applied to the San Francisco master drainage
plan for  abatement  of combined sewer
overflows

9  Updating Version

Version  1  (1977)

10. Input Data Requirements:

•  SCS, build-up, and wash-off parameters
•  Runoff coefficient and soil type
                                                                               A 31

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 11. Simulation Output:

 •  Storm event summaries (runoff
   volume, concentrations, and loads)
 •  Summaries of storage and treatment,
   utilization, total overflow loads and
   concentrations
 •  Hourly hydrographs and pollutographs
   (concentration vs  time)
 •  Statistical summaries on annual and
   total simulation period basis
   (percentage of runoff passing through
   storage and the number of overflows)

 12. References Available:

 Abbott, J  1977 Guidelines for
 calibration and application of STORM.
 U.S. Army Corps of Engineers,
 Hydrologic Engineering Center  Davis,
 CA Training Document No 8

 Abbott, J  1978.  Testing of several
 runoff models on an urban watershed.
 ASCE Urban Water Resources Research
 Program.  ASCE, New York, NY
 Technical Memorandum No 34
Donigian, A S , Jr , and W C  Huber  1991
Modeling of nonpoint source water quality m
urban and non-urban areas. U S
Environmental Protection Agency,
Environmental Research Laboratory, Athens,
Georgia EPA/600/3-91/039

Hydrologic Engineering Center. 1977
Storage, Treatment,  Overflow, Runoff
Model, STORM, User's manual. Generalized
Computer Program 723-S8-L7520  U S
Army Corps of Engineers, Davis,  CA

Najanan, T 0 , T T  Griffin, and V K
Gunawardana  1986 Development impacts
on water quality  A case study Journal of
Water Resources Planning and Management,
ASCE,  112(1) 20-35

Shubmski, R P , A J  Knepp, and C R
Bristol  1977  Computer program
documentation for the continuous storm
runoff model SEM-STORM  Report to the
Southeast Michigan Council of
Governments, Detroit, Ml
A 32

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    ANSWERS:  Area/ Nonpoint Source Watershed Environment
                            Response Simulation
 1. Distributor

 Dr  David Beasley
 Department of Agriculture Engineering
 North Carolina State University
 Raleigh, North Carolina
 (919) 515-2694

 2  Type of Modeling

 •  Simulation of agricultural watersheds
   with emphasis on erosion and
   sediment yield
 •  Distributed simulation using a grid
   system
 •  Storm event simulation
 •  Single and diffuse source/release
 •  Screening and intermediate
   applications
 •  Evaluation of BMPs

3  Model Components:

 •  Rainfall/runoff assessment
 •  Overland flow and channel  flow
 •  Loading of nutrients and pesticides
 •  Erosion, sediment transport, and
   deposition

4  Method/Techniques

This model simulates the effects of land
use, management, and conservation
practices on the quality and quantity of
water in a watershed  The hydrology
component is based on surface and
subsurface water movement relationships
using a modified form of the Holton
infiltration model  Erosion processes are
predicted by an event-based particle
detachment and transport model  The
quality component was added to the model
to compute pollutant loadings based on
correlation relationships between
concentration, sediment yield, and runoff
volume Improvements to the pollutant
loading and transformation routines have
been incorporated by Dillaha et al (1988)

5  Applications

•  Hydrologic and erosion response of
   agriculture land and construction sites
•  Movement of water m overland,
   subsurface, and channel flow phases
•  Identification of critical areas for erosion
   and sedimentation control
•  Siting and evaluation of BMPs

6  Number of Pollutants

Nutrients (phosphorus and nitrogen) and
sediment  (Some versions include
pesticides )

7  Limitations:

•  Mainframe computer required for large
   watershed simulation
•  Complexity  of input data file
•  Snowmelt processes and pesticide
   modeling are not included
•  No chemical transformation of  nitrogen
   and phosphorus
•  Small time steps are necessary for finite
   difference algorithms and restrict the
   simulation to a single event
                                                                               A 33

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•  Requires small element grid, assumes
   homogeneous condition within each
   element

8. Experience:

Applied successfully in Indiana on
agricultural watersheds and construction
sites for best management practice
(BMP) evaluation Evaluated the relative
importance of point and nonpomt source
contributions to Sagmaw  Bay

9. Updating Version:

   N/A

10. Input Data Requirements

Detailed description of the watershed
topography, drainage network, soils, and
land use (available from USDA-SCS soil
surveys, land use, and cropping surveys)

11 Simulation Output:

 •  Alternative erosion control
   management practices on an element
   basis or entire watersheds (flow and
   sediment)
 •  Limited graphical representation of
   output results

 12. References Available.

Amm-Sichani, S. 1982 Modeling of
phosphorus transport in surface runoff
from agricultural watersheds  Ph D
Thesis, Purdue University, W Lafayette,
IN.
Beasley, D.B  and L F  Huggms 1981
ANSWERS User's Manual.  U S
Environmental Protection Agency,  Region
V Chicago, IL  EPA905/9-82-001

Beasley, D B  1986 Distributed parameter
hydrologic and water quality modeling  In
Agricultural Nonpoint Source Pollution:
Model Selection and Application, ed  A
Giorgmi and F Zingales, pp 345-362

Diilaha, T  A  III, D B  Beasley,  and L F
Huggms  1982  Using the ANSWERS model
to estimate sediment yields on construction
sites  Journal of Soil and Water
Conservation 37(2) 117-120

Diilaha, T  A , C D  Heatwole, M R Bennett,
S Mostaghimi, V O Shanholtz, and B B
Ross   1988  Water quality modeling for
nonpomt source pollution control planning
Nutrient transport. Virginia Polytechnic
Institute and  State University, Dept of
Agricultural Engineering Report No  SW-88-
02

Donigian,  A S , Jr , and W C  Huber 1991
Modeling  of nonpomt source water quality in
urban and non-urban areas. Environmental
Protection Agency, Environmental Research
Laboratory, Athens, Georgia  EPA/600/3-
91/039

Freedmann, PL  and D W  Dilks  1991
Model capabilities - A user focus  In EPA
 Workshop on the Water Quality-based
Approach for Point Source and Nonpoint
Source Controls, June 1991  pp  26-28.
EPA 503/9-92-001
A 34

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 DR3M-QUAL:  Distributed Routing Rainfall Runoff Model - Quality
1. Distributor:

Ms Kate Flynn
410 National Center
U S Geological Survey
Reston, VA 22092
(703)  648-5313

2  Type of Modeling

•  Urban stormwater pollutant loads
•  Continuous simulation
•  Continuous, intermittent, and diffuse
   source/release
•  Intermediate and detailed applications

3  Model Components

•  Rainfall/runoff assessment
•  Water quality  analysis

4. Method/Techniques:

This model simulates rainfall/runoff
processes (hydrographs) and water
quality processes (pollutographs) in urban
and other areas   The kinematic wave
method is used over multiple
subcatchments to predict runoff from
rainfall and drainage pathways  A built-in
optimization routine and a storage-
indication routine are available for
estimating water quantity parameters
Exponential build-up and wash-off
functions derived from experience with
model calibration are applied to  predict
water quality  Empirical equations use
relationships between sediment yield and
runoff volume and peak to simulate
erosion The erosion parameters are
selected based on the USLE The
transport process is modeled assuming plug
flow and using a Lagrangian scheme.
Calibration is required for accurate quality
predictions  However, default values may
be used for screening level analysis

7. Applications

•  Rainfall/runoff assessment
•  Surface water quality analysis

6. Number of Pollutants:

•  Sediment,  nitrogen, and phosphorus,
   metals, and organics

7. Limitations.

•  No interaction among quality parameters
•  Sediment transport simulation is weak

8  Experience.

The program has been extensively reviewed
within the USGS and applied to several
urban modeling studies, including South
Florida (1980), Rochester  (1985  and 1988),
Anchorage (1986), Denver (1987), and
Fresno (1988)

9. Updating Version.

   N/A

10. Input Data Requirements*

•  Subcatchment data area,
   imperviousness, length, slope,
   roughness, and infiltration parameters
                                                                               A 35

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 •  Trapezoidal or circular channel
   dimensions and kinematic wave
   parameters
 •  Stage-area-discharge relationships for
   storage basins
 •  Water quality parameters, including
   build-up and wash-off coefficients

 13. Simulation Output:

 •  Time series of runoff hydrographs and
   quality pollutographs (concentration or
   load vs. time) at any location in the
   drainage system
 •  Summaries for storm events
 •  Graphical output of water quality and
   quantity analysis

 14. References Available

 Alley, W.M. 1981  Estimation of
 impervious-area wash-off parameters
 Water Resources Research 17(4) 1161-
 1166.

 Alley, W.M. 1986  Summary of
 experience with the distributed routing
 rainfall-runoff model (DR3M) In Urban
 Drainage Modeling  ed C Maksimovic
 and M.  Radojkovic  pp 403-415
 Pergamon Press, New York

 Alley, W.M. and P E. Smith  1981
 Estimation of accumulation  parameters
 for urban runoff quality modeling  Water
 Resources Research 17(6) 1657-1664

 Alley, W.M. and P E Smith  1982a
 Distributed Routing Rainfall-Runoff Model
 - Version II. U.S. Geological Survey,
 Reston, VA.  Open file report 82-344

 Alley, W.M and P.E. Smith  1982b
 Multi-event urban runoff quality model.
 U.S. Geological Survey  Reston, VA
 Open file report 82-764,
Brabets, T P 1987  Quantity and quality of
urban runoff from the Chester Creek basin
Anchorage, Alaska. U S Geological Survey,
Anchorage, AL Water-Resources
Investigations Report 86-4312

Donigian, A S , Jr , and W C Huber 1991
Modeling of nonpoint source water quality in
urban and non-urban areas  U S
Environmental  Protection Agency,
Environmental  Research Laboratory, Athens,
Georgia EPA/600/3-91/039

Quay, J R and P E  Smith  1988 Simulation
of quantity and quality of storm runoff for
urban catchments in Fresno, California. U S
Geological Survey, Sacramento,  CA  USGS
Water-Resources Investigations Report 88-
4125,

Kappel, W M , Yager, R M and P J
Zarnello  1986 Quantity and Quality of
Urban Storm Runoff in the Irondequoit Creek
Basin near Rochester, New York, Part 2
Quality of Storm Runoff and Atmospheric
Deposition, Ramfall-Runoff-Quality Modeling,
and Potential of Wetlands for Sediment and
Nutrient Retention U S Geological Survey,
Ithaca, NY USGS Water-Resources
Investigations  Report 85-4113

Lmdner-Lunsford, J B and S R Ellis 1987
Comparison of Conceptually Based and
Regression Rainfall-Runoff Models, Denver
Metropolitan Area, Colorado, and Potential
Applications in Urban Areas. U S Geological
Survey, Denver, CO USGS Water-Resources
Investigations  Report 87-4104,

Zarnello, P J 1988  Simulated water-quality
changes in detention basins In Design of
Urban Runoff Quality Controls, ed L A
Roesner, B  Urbonas, and M B Sonnen
Proceedings of Engineering Foundation
Conferences, Potosi, Ml. ASCE,  New York
pp 268-277
A 36

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            SWRRB: Simulation for Water Resources in Rural Basins
1. Name of Distributor.

Dr  Jimmy R  Williams
Agriculture Research Service
U S  Department of Agriculture
Grassland, Soil and Water Research Lab
Temple, TX 76502
(817) 770-6502

2 Type of Modeling

•  Stormwater from agricultural
   watersheds
•  Diffuse source/release
•  Screening, intermediate, and detailed
   applications

3  Model Components

•  Rainfall/runoff assessment
•  Surface water quality analysis
•  Soil/groundwater contamination

4  Method/Techniques

This program evaluates basin-scale
(large, complex, and rural basins) water
quality  Surface runoff is described by
the SCS curve number equation  The
modified  Universal Soil Loss Equation
(USLE) is applied to  simulate erosion for
each basin  Degradation and deposition
are considered for the channel and
floodplam sediment  routing model
Bagnold's stream power concept  is used
for degradation processes, while the fall
velocity of sediment particles is used for
deposition  Return flow, percolation, and
crop growth are calculated  Soluble and
sediment-attached pollutants are
considered for pollutant transport
Nutrients (nitrogen and phosphorus) are
simulated by using relationships between
chemical concentration, sediment yield, and
runoff volume  Calibration is not specifically
required but is desirable

5. Applications

•  Water and sediment yields from ungaged
   rural basins
•  Return flow, pond and reservoir storage,
   and crop growth
•  Sediment movement through ponds,
   reservoirs, streams, and valleys
•  Flood routing

6. Number of Pollutants.

Sediment components, nitrogen,
phosphorus, and pesticides

7  Limitations:

•  Nutrient transformations are not
   evaluated

8  Experience:

The model was tested on 11  large
watersheds  The testing results showed that
SWRRB can simulate water and sediment
yield under  a wide range of soils, climate,
land use, topography, and management
systems

9  Updating Version

   N/A
                                                                                A 37

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10. Input Data Requirements-

*  Meteorological data (daily precipitation
   and solar radiation)
•  Soils, land use, and fertilizer and
   pesticide application

11. Simulation Output.

*  Daily runoff volume and peak rate,
   sediment yield, evapotranspiration,
   percolation, return flow, and pesticide
   concentration in both runoff and
   sediment
•  Nutrient concentrations/loads

12. References Available:

Arnold, J.G., J.R  Williams, A D Nicks,
and N.B. Sammons  1989  SWRRB, a
basin scale simulation model for soil and
water resources management Texas
A&M Press.

Arnold, J G., and J.R  Williams  1987
Validation of SWRRB - simulator for
water resources in rural basins  Journal of
Water Resources Planning and Management
113(2) 243-256

Computer Science Corporation. 1980
Pesticide runoff simulator user's manual.
U S  Environmental Protection Agency,
Office of Pesticides and Toxic Substances,
Washington, DC

Donigian, A S , Jr , and W C Huber  1991
Modeling of nonpomt source water quality in
urban and non-urban areas  U S
Environmental Protection Agency,
Environmental Research Laboratory, Athens,
Georgia  EPA/600/3-91/039

Williams, J R ,and H D  Berndt 1977
Sediment yield prediction based on
watershed  hydrology  Transactions of the
ASAE 20(6) 1100-1104

Williams, J R , A D  Nicks, and J G Arnold
1985  Simulator for water resources in rural
basins Journal of Hydraulic Engineering
ASCE 111(6) 970-986
A.38

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               SWMM:  Storm Water Management  Model
 1  Name of Distributor

 Mr. David Disney
 U S  Environmental Protection Agency
 Environmental Research Laboratory
 College Station Road
 Athens, GA 30613
 (404) 546-3123

 2  Type of Modeling

 •  Urban stormwater processes
 •  Continuous and storm event
   simulation with variable and user-
   specified time steps (wet and dry
   weather periods)
 •  Single, continuous, intermittent,
   multiple, and diffuse source/release
 •  Screening, intermediate, and detailed
   planing applications
 •  Evaluation of BMPs and development
   of design criteria

 3  Model Components

 •  Rainfall/runoff assessment
 •  Water quality analysis
 •  Soil/groundwater contamination
 •  Point source inputs available

4  Method/Techniques

This  model simulates overland water
 quantity and quality produced by storms
 in urban watersheds. Several modules or
 blocks are included to model a wide
range of quality and quantity watershed
processes  A distributed parameter sub-
model (RUNOFF) describes runoff based
on the concept of surface storage
balance  The rainfall/runoff simulation is
accomplished by the non-linear reservoir
approach  The lumped storage scheme is
applied for soil/groundwater modeling  For
impervious areas, a linear formulation is
used to compute daily/hourly increases in
particle accumulation   For pervious areas, a
modified Universal Soil Loss Equation (USLE)
determines sediment load  The concept of
potency factors is applied to simulate
pollutants other than sediment.

5  Applications

•  Urban stormwater and combined systems
•  Surface water routing
•  Urban watershed analysis, including
   baseflow contributions

6  Number of Pollutants

Limited to ten pollutants, including sediment

7  Limitations.

•  Lacks graphics routines
•  Quality and solids transport simulations
   are weak

8. Experience:

Applied to urban hydrologic quantity/quality
problems in over 100 locations in the United
States and Canada

9  Updating Version:

Version 404 (1989)
                                                                                A 39

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10. Input Data Requirements

•  Rainfall hyetographs, antecedent
   conditions, land use, and topography
•  Dry-weather flow and soil
   characteristics
•  Gutter/pipes - hydraulic inputs
•  Pollutant accumulation and wash-off
   parameters
•  Hydraulics and kinetic parameters

11. Simulation Output:

•  Time series of flow, stage, and
   constituent concentration at any point
   in watershed
•  Seasonal and annual summaries

12. References Available

Cunningham, B A and W C  Huber
1987. Economic and predictive reliability
implications of stormwater design
methodologies, Florida Water Resources
Research Center, University of Florida,
Gainesville, FL Publication No  98

Dever, R J., Jr ,  L A  Roesner, and J A
Aid rich. 1983 Urban highway storm
drainage model vol. 4, Surface runoff
program user' manual and
documentation.  Federal Highway
Administration, Washington, DC
 FHWA/RD-83/044.
Dever, R J , Jr , L A Roesner, and D-C ,
Woo  1981 Development and application of
a dynamic urban highway drainage model In
Urban Stormwater Hydraulics and
Hydrology, Proceedings of the Second
International Conference on Urban Storm
Drainage, Urbana, IL pp 229-235   Water
Resources Publications, Littleton, CO

Donigian, A S , Jr , and W C  Huber  1991
Modeling of nonpomt source water quality in
urban and non-urban areas U S
Environmental Protection Agency,
Environmental Research Laboratory, Athens,
Georgia EPA/600/3-91/039

Huber, W C 1986 Deterministic Modeling
of Urban Runoff Quality In Urban runoff
pollution, Proceedings of the NA TO
Advanced Research Workshop on Urban
Runoff Pollution, Montpellier, France ed
H C Torno, J  Marsalek, and M  Desbordes
pp 167-242   Series  G Ecological
Sciences  Vol  10  Springer-Verlag, New
York

Huber, W C 1989 User feedback on public
domain software  SWMM case study  In
Proceedings of the Sixth Conference on
Computing in Civil Engineering, Atlanta,
Georgia  American Society of Civil
Engineers, New York,  NY

Huber, W C and  R E  Dickinson 1988
Storm Water Management Model Version 4,
User's manual U S Environmental
Protection Agency, Athens, GA  EPA600/3-
 88/001a (NTIS PB88-236641/AS)
A 40

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         HSPF: Hydrological Simulation Program - FORTRAN
1. Distributor-

Mr David Disney
U S  Environmental Protection Agency
Environmental Research Laboratory
College Station Road
Athens, GA 30613
(404) 546-3123

2. Type of Modeling

•  Pollutant load and water quality in
   complex watersheds
•  Continuous and storm event
   simulation
•  Single, continuous, intermittent,
   multiple, and diffuse source/release
•  Screening, intermediate, and detailed
   applications
•  BMP evaluation and design criteria

3  Model Components:

•  Watershed hydrology assessment
•  Surface water quality analysis
   (conventional and toxic organic
   pollutants)
•  Soil/groundwater contaminant runoff
   processes  with mstream hydraulic and
   sediment-chemical interactions
   (saturated  and unsaturated zones)
•  Pollutant decay and transformation

4. Method/Techniques.

This  model calculates surface and
subsurface pollutant transport from
complex watersheds to receiving waters
Hydrolysis, oxidation, photolysis,
biodegradation, volatilization, and
sorption are used to describe the transfer
and reaction processes  First-order kinetic
processes are employed to model sorption
Water quality is simulated by a lumped
parameter model  Three sediment types
(sand, silt, and clay) and a single organic
chemical as well as transformation products
of that chemical can be simulated   The
program can assess the water quality
impacts of alternative best management
practices (BMPs)  Calibration is required for
model application  Because of the modular
approach, detail of application can be varied
depending on data availability and  modeling
needs

5  Applications

•  Surface and subsurface pollutant
   transport to receiving water with
   subsequent simulation of mstream
   transport and transformations
•  Watershed hydrology and water quality
   for both conventional and toxic organic
   pollutants
•  Evaluation of BMPs and development of
   design criteria

6  Number of Pollutants

Seven pollutants three sediment
components (sand, silt, and clay), one
pesticide or other toxic pollutant (user-
specified), BOD, ammonia or nitrate, and
orthophosphate

7  Limitations

•  Limited to well-mixed rivers  and
   reservoirs
•  Extensive water quality sampling data
   required for calibration or verification
                                                                                A 41

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*  Highly trained staff required for model
   application

8. Experience:

•  Developed based on field data
   gathering and testing at an Iowa site
•  Recently used to model erosion and
   BMP effects on a west Tennessee
   watershed with calibration and
   verification
•  Extensively applied in a wide variety
   of hydrologic and water quality
   studies

9. Updating Version:

Version 9.01, 1989

10. Input Data Requirements:

 •  Continuous rainfall records
 •  Continuous records of
   evapotranspiration, temperature, and
   solar intensity
 •  A large  number of  parameters need to
   be specified (some default values are
   available)

 11. Simulation Output.

 •  Time series of the  runoff flow rate,
   sediment load,  and nutrient and
   pesticide concentrations
 •  Time series of water quantity and
   quality at any point in a watershed
 •  Frequency and duration analysis
   routine

 12. References Available.

 Barnwell, T O., and R Johanson  1981
 HSPF: A comprehensive package for
 simulation  of watershed hydrology and
 water quality. In Nonpoint pollution
 control: tools and techniques for the
future. Interstate Commission on the
Potomac River Basin, Rockville, MD

Barnwell, T O ,and J L  Kittle  1984
Hydrologic Simulation Program - FORTRAN
Development, maintenance and application
In Proceedings Third International
Conference on Urban Storm Drainage.
Chalmers Institute of Technology, Goteborg,
Sweden

Bicknell, B R , A S Donigian, and T O
Barnwell 1984  Modeling water quality and
the effects of best management practices in
the Iowa River basin  Journal of Water
Science Technology 17 1141-1153

Donigian, A S , J C  Imhoff, B R Bicknell,
and J L Kittle  1984 Application Guide for
the Hydrologic Simulation Program -
FORTRAN  Environmental Research
Laboratory, U S Environmental Protection
Agency, Athens, GA EPA 600/3-84-066

Donigian, A S , D W  Meier, and P P
Jowise 1986  Stream transport and
agricultural runoff for exposure assessment.
A methodology Environmental Research
Laboratory, U S EPA, Athens, GA
EPA/600/3-86-011

Johanson, R C , J C  Imhoff, J L  Kittle,
A S Donigian  1984 Hydrological
Simulation Program - FORTRAN (HSPF).
User's manual for release 8.0. ,
Environmental Research Laboratory, U S
Environmental Protection Agency, Athens,
GA EPA600/3-84-066

Schnoor, J L , C Sato, D  McKetchnie, D
Sahoo  1987  Processes, coefficients, and
models for simulating toxic organics and
heavy metals in surface waters.
Environmental Research Laboratory, U.S
Environmental Protection Agency, Athens,
GA EPA/600/3-87/015.
A.42

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