Development of a Common
Wind and Water Erosion Model
Dennis C. Flanagan
Agricultural Engineer
USDA-Agricultural Research Service
National Soil Erosion Research Laboratory
West Lafayette, Indiana, USA
Outline
 Brief history of erosion prediction
technology development in the U.S.
 User needs for a common water and
wind erosion model.
 Plans for model development.
 Progress to date.
History of Erosion Prediction
Technology Development in U.S.
 Universal Soil Loss Equation (USLE)
developed from ~1954 to 1978.
 Revised Universal Soil Loss Equation
(RUSLE/RUSLE2) from ~1987 to 2002.
 Wind Erosion Equation (WEQ) from ~1953 to
1965 and Revised WEQ from ~1990 to 1998
 Wind Erosion Prediction System (WEPS)
model from 1985 to 2007
 Water Erosion Prediction Project (WEPP)
model from 1985 to 2007
USLE
 Developed from ~1954-1978 to predict longterm average annual soil loss on hillslopes.
 Soil conservation experiment station data
from the 1930’s to 1950’s was utilized in its
development (over 10,000 plot-years).
 First publication on USLE was in 1961.
 Implemented in SCS field offices during the
1960’s.
 USLE is an empirical model:
A=RKLSCP
RUSLE / RUSLE2
 Developed from ~1987 to ~2002.
 RUSLE was implemented in SCS field offices
in paper form only in ~1993.
 RUSLE2 was implemented in NRCS field
offices in ~2002.
 RUSLE/RUSLE2 are empirical models with
some process-based enhancements.
 Improvements to USLE R, K, C factors.
 Extremely large management rotation
databases for every state in the U.S.
 Maintained by ARS-Oxford, MS.
WEQ / RWEQ
 WEQ was developed from ~1953 to 1965 to
predict soil loss from wind erosion on an
average annual basis.
 WEQ was adopted by the SCS for predictions
of soil erosion by wind, and is used mainly in
the western U.S.
 The difficulty of use of WEQ prompted
development of several computerized
versions by both ARS and SCS/NRCS.
 A revised wind erosion equation (RWEQ) was
developed by ARS from ~1990 to 1998, but no
widespread adoption by NRCS is planned.
 RWEQ is maintained by ARS-Lubbock.
WEPS
 Process-based, continuous simulation,
wind erosion model.
 Developed from 1985-2007 by ARSWind Erosion Research Unit (WERU) in
Manhattan, Kansas.
 Field testing and implementation by
NRCS has begun in last 2 years.
 Recently WEPS has incorporated
WEPP model hydrology to decrease
run time.
WEPS Windows Software
WEPP
 Process-based, continuous simulation
water erosion model.
 Developed from 1985-2007 by ARS,
SCS/NRCS, FS, BLM, WSU and others.
 WEPP model is maintained by ARSNational Soil Erosion Research
Laboratory in West Lafayette, Indiana.
 Large number of users, both within and
outside U.S., including Forest Service,
BLM, universities, consultants.
WEPP status
 Current public model version is
v2006.5
 V2006.5 contains recent updates to
water balance, subsurface lateral flow,
perennial plant growth – to better
simulate forests on shallow soils
above bedrock.
 Variety of user interfaces – Windowsbased, Web-based, and GIS-linked.
WEPP Windows Interface
WEPP Web-based Interfaces
Separation of Wind / Water Research
 Initial research studies were focused in areas
with specific erosion concerns – water erosion
in the eastern and central U.S., and wind
erosion in the Great Plains.
 ARS programs, experiment stations, research
units, and funding were separated between
water and wind erosion locations since the
inception of the agency in 1953.
 Process-based modeling efforts that began in
1985 (WEPP and WEPS) were for the most part
separate, due to the existing institutional
framework.
This Separation resulted in:
 Two separate teams of ARS scientists building
continuous process-based simulation models.
 Two models that were required to simulate
many of the same physical processes (soil
water balance, hydrology, plant growth, residue
decomposition, soil disturbance by tillage, etc.).
 Separate model interfaces and databases.
 Large potential for different model results (for
crop growth, runoff, etc.) for same site of
application, since different science
implemented in the two different models.
In 2004
 The Natural Resources Conservation
Service re-evaluated its need for
erosion prediction technology from
ARS.
 High priority long-term need of NRCS
was development of a common wind
and water erosion process model, to
work with a single interface and
database and give consistent results
for plant growth, water balance, crop
yield, etc.
From March 1, 2004 Letter from NRCS:
“For the long term, NRCS proposes to collaborate
with ARS to build a single process based model to
make erosion prediction calculations. NRCS
proposes that this model be capable of making
rainfall induced rill and interrill erosion
computations, as well as computations for wind
erosion together or independently of one another.
This model would naturally incorporate the
technologies currently in WEPS, the Water Erosion
Prediction Project (WEPP), and those found in the
Water Erosion Prediction Project - Simulation of
Production and Utilization of Rangelands (WEPPSPUR). Unlike the current models, the model
proposed by NRCS would operate as a single
decision support tool, and use common
databases.”
- Larry Clark, NRCS Deputy Chief Science & Technology
2004 ARS NSERL Erosion Prediction Program
Redirection
 Modification of NSERL erosion prediction CRIS
research project
– Stop new development work on existing WEPP
model science and interface code
– Minimize resources towards current WEPP
model code and user support
– Focus majority of resources towards
development of new wind and water erosion
model.
 Top short-term priority - Incorporation of WEPP
hillslope erosion science within the Object
Modeling System (OMS) being developed by ARSGPSRU in Fort Collins, CO.
2004 Project Objectives
 Short-term
– Incorporate the WEPP hillslope erosion
code within OMS.
– Evaluate the feasibility of using OMS as
the platform for the full combined wind
and water erosion model.
– Develop a complete project plan for
development of the new model.
 Long-term
– Develop a fully functional continuous
simulation wind and water erosion
process model for field application by
2011.
New CRIS project
 Entitled “Common Modular Wind and Water
Erosion Modeling for Conservation
Planning”
 Recently approved (12/2006) through OSQR
 2006-2011 Develop a common wind and
water soil erosion model for use by NRCS
field offices.
 Utilize water erosion components from
WEPP model, and wind erosion
components from WEPS model.
 Develop necessary interfaces and
databases for the new modeling system.
New CRIS Project Objectives
 Integrate the WEPP and WEPS model erosion
technologies through the use of the Object
Modeling System (OMS) into a single wind/water
erosion prediction system using common
databases and interfaces at the plot and field scale.
 Incorporate, test and verify new erosion science or
related components, such as winter processes,
tillage erosion, ephemeral gully erosion, irrigation
erosion and rangeland erosion, into the integrated
erosion prediction system.
 Cooperate with all ARS scientists and NRCS staff
involved with the CEAP effort to extract relevant
modules from existing models and integrate them
into the OMS for development of regional water and
air quality models at the plot, field, and watershed
scales.
New CRIS Project Milestones
 12 months
- Development of wind detachment component in OMS
- Testing/validation of hydrologic & water erosion
prototype
- Develop user requirements for system with major user
agencies
- Addition of dynamic water erosion calculations
 24 months
– Development of detailed software design document.
– Unified Plant Growth Model incorporated into OMS.
– Prototype OMS wind-water model with most needed
components.
– Validation of single event wind erosion predictions.
– Addition of tillage erosion modules into OMS.
New CRIS Project Milestones
 36 months
–
–
–
–
Development of ARS interface for testing/validation
Development of core combined model databases
New winter components added into OMS
Addition of tillage erosion simulation into wind-water model
 48 months
– Development of NRCS interfaces for model testing and training.
– Validation studies on wind, water and tillage erosion predictions.
– Addition of rangeland components
 60 months
– Integrated field-scale erosion prediction system initially for cropland
applications and prediction of wind, water or tillage erosion delivered to
NRCS.
– Model technical and user documentation written.
– Creation of irrigation erosion modules.
– Testing of rangeland and irrigation erosion modules
– Prototype regional field-to-watershed model for CEAP, integrating
appropriate modules from wind-water system.
Two Development Paths
 First Path – Extract individual
components from WEPP and WEPS
and other relevant models. Develop
modules within OMS from these
components, then build new model
within OMS. (as written in Plan)
 Second Path – Utilize WEPS model
code as the basic framework and
add WEPP model water balance,
runoff, water erosion components.
Object Modeling System (OMS)
What is the Object Modeling System?
 An object-oriented toolset to build,
run, and deploy simulation models
 An object-oriented framework for
the management of reusable
simulation component libraries
 A collaboration infrastructure for
common model development
Object Modeling System
 Modeling framework to support the
model development/application
lifecycle
 OMS Facilitates:
Component
– Code reuse and sharing
Component
Integration,
Development,
– Capture of legacy knowledge
Model Development
Testing
– Collaborative development
– Database access
– Verification/validation
Model
Application,
– QA/QC
Analysis
– Maintenance and change
management
Components in OMS
 “Components are software
units that are contextindependent both in the
conceptual and technical
domain”
 Well adopted methodology for
software reuse
 Scientific component
 Infrastructure
component
 Utility component
 …
Internal hidden
behavior
Input
Component
Well known interfaces
Component
Output
Scientific Component
 Represents a basic processing unit
 Conceptual purpose
– Runoff computation
– Soil erosion computation
–…
Input


Components are “tagged” by implementing
interfaces:
– Native, Runable, Stateful, Visualizable
Customization by implementing these
interfaces:
– Minimum: Runable
Component
Component
Output
Step 1: Create Components
Input
Data
Create Components
Step 2: Create Model
Component Library
New Model - Training
Step 3: Build Model From Components
Attributes
Component
Connectivity
(Hookups)
Model Building
Structures
Step 4: Run Assembled Model
Modeling
Projects
Component
Library
Component
Editor
Output
Analysis
OMS also has
output graphic
and parameter
editing capabilities
Assembled
Model
Parameter
Editor
OMS Workflow Summary
Component
Builder
Publish
Model
Builder
Integrate
Component
Library
Output
Analysis
Execute
Analyze
Model
Runtime
Data Analysis
Model Application
Component Integration
Component Library Management
Component Development
First Development Path
 Extract individual components from
WEPP and WEPS and other relevant
models. Develop modules within OMS
from these components, then build new
model within OMS.
 Advantages – modular approach best for long-term
agency code maintainability, can access and use
existing components in OMS library, NRCS desires new
model development in OMS, multiple spatial
representations for wind and water may be easier.
 Disadvantages - OMS system not fully developed and
easy to use, incorporation of legacy models in OMS
can be difficult and time-consuming, agencies’
continued support of OMS is uncertain.
Path 1 - Progress to Date
 WEPP hillslope water erosion code
extracted and stand-alone program
created (2004).
 WEPP hillslope surface hydrology
(infiltration, runoff) extracted and standalone program created (2005).
 Stand-alone hydrology and erosion code
converted to components in OMS (2005).
 Single storm and continuous
hydrology/erosion model created in OMS
(2005).
Approach
 Initially in 2004-2005
– Convert hillslope erosion
component from WEPP into a
standalone Fortran program.
– Test and verify standalone program
against original WEPP v2004.7
model
– Incorporate standalone program into
OMS, test and verify.
 September-October 2004
– Extracted relevant hillslope erosion code
from WEPP v2004.7 for single storm.
– Removed all common blocks and moved
only necessary variables into argument lists.
– Created input files to just conduct single
storm water erosion calculations.
– Tested standalone for range of inputs –
slope lengths, gradients, and shapes and
compared to WEPP v2004.7 output.
– This resulted in corrections to the
standalone code and ultimately a verified
single storm program that operated for a
single spatial plane.
Results of Final 10/2004
Standalone Verification Tests
Standalone Sed. Yield
(tonnes/ha)
Standalone vs WEPP (Sediment Yield)
800
700
y = 0.9996x
R2 = 1
600
500
400
300
200
100
0
0
200
400
600
WEPP Sediment Yield (tonnes/ha)
800
 January-February 2005
– Made code active to handle multiple
spatial planes.
– Modified input files to provide
information necessary for multiple
planes.
– Tested standalone for range of inputs –
1, 2, 4, 10 overland flow elements and
compared to WEPP v2004.7 output.
– This resulted in corrections to the
standalone code and ultimately a
verified single storm program that
operated for a multiple spatial planes.
This contained spatial looping similar to
WEPP in the standalone MAIN program.
Standalone Fortran erosion code: 2/2005
 MAIN program and 30 subroutines under it. MAIN
contained spatial plane (iplane) looping similar to WEPP.
 Reads from a single input file and creates 2 output files,
almost identical to current WEPP outputs.
 Will compile and run with standard F-77 to F-95 compilers.
 March-April 2005
– Spatial looping in MAIN program and all subroutines
removed, so that code could be better utilized within
OMS with other models, as well as with potential
spatial representation needed for wind erosion.
– Existing standalone Hydrology component (based
largely on WEPP) from Ascough was converted into
a format ready for OMS inclusion.
– Pass file creation with information generated by
Hydrology standalone and needed for Erosion
standalone calculations was added to Hydrology
code.
– This work resulted in standalone Hydrology and
Erosion code that would function in tandem to do
infiltration/runoff calculations (Green-Ampt), runoff
hydrograph and peak rate calculation (kinematic
wave), and hillslope interrill/rill erosion calculations
for a single storm/single plane.
Standalone Fortran hydrology code: 4/2005
 MAIN program and 19 subroutines under it.
 Reads from a single input file and creates 2
output files: hydrology output identical to WEPP,
and a hydrology-to-erosion pass file (runoff
depth, peak rate, intensities, durations).
 June 2005
– Individual Hydrology and Erosion
Models were created within OMS,
tested and verified against the
standalone programs.
– A linked hydrology and erosion model
for a single storm and spatial plane
was created in OMS.
– The linked OMS model was expanded
to successfully perform spatial
(multiple planes) and temporal
(multiple storm days) looping.
OMS individual Hydrology and Erosion
Models: 6/2005
 To build models in OMS, the functionality in the standalone
Fortran MAIN programs had to be duplicated.
 All processing logic in existing MAIN had to be either
moved to one of the existing subroutines, or a new
component created.
OMS with 6/2005 Temporal/Spatial Erosion Model
Erosion Model
Output window showing
model screen outputs
Erosion Model – named “erroder” here
Conditional – Daily Time step –
goes through loop for
number of days read in from
climate file.
Conditional – to do infiltration,
runoff and erosion
calculations, only if there is
rainfall on the day
Conditional – to do Erosion
Calculations only if there
is outflow from or inflow
to plane.
Path 1 - Progress to Date (cont.)
 Continuous water balance model (based
on RZWQM) constructed in OMS, and
hydrology and water erosion modules
linked into this (2006).
 Wind detachment stand-alone code from
WEPS converted into an OMS module
(2006).
 Prototype wind and water combined
model constructed in OMS, linking wind
detachment module with water balance
model (2006).
10/2006 Wind & Water Model Prototype in OMS
Wind & Water Model
Prototype in OMS
Water Balance Initializations
Daily loop
Potential Evapotranspiration Calculations
24 Hour loop
Infiltration Calculations
Soil Water Redistribution
Erosion by Water Components
Erosion by Wind Component
OMS Model water erosion outputs
OMS Model wind erosion outputs
Future OMS Work
 Add more components (plant growth,
parameter estimation, etc.) to library and
link these with existing prototype.
 Properly set up spatial looping to
represent both a gridded wind
detachment region and a water erosion
hillslope profile.
 Test OMS models against original
WEPP/WEPS models, and compare to
field experiment data.
Second Development Path
 Utilize the WEPS model code as the basic
framework and add WEPP model water
balance, runoff, water erosion
components.
 Advantages – WEPS is already being implemented and tested by
NRCS, WEPS databases and interface already available, WEPS has
recently incorporated WEPP water balance/hydrology code.
 Disadvantages - WEPS code can only simulate single accounting
region – does not provide spatial representation currently in WEPP
or in water erosion model in OMS, does not provide modules for
OMS code repository, does not help with agency goals of more
maintainable and reusable model components.
Path 2 - Progress to Date
 WEPP Water Balance incorporated into WEPS
model code (2005-2006).
 WEPP kinematic wave computations for
prediction of peak runoff rate, and also
prediction of effective rainfall intensity and
associated durations added to WEPS code
(2006)
 WEPP hillslope (interrill/rill) erosion code
added to modified WEPS model (2007), and is
currently being tested and parameters linked
to WEPS values where possible.
Path 2 – Future Work
 Complete linkage of WEPP parameters to
WEPS values.
 Where not possible or feasible to utilize
existing WEPS information, need to add WEPP
components to generate necessary
information (e.g. water sediment particle size,
water erodibility parameterization/updating)
 Test and verify combined WEPS/WEPP code
against individual models.
 Modify WEPS interface/database to provide
additional data necessary for WEPP.
 Possibly develop a new combined interface.
Summary
 Current development efforts are towards
creation of a combined wind and water
model based upon WEPP and WEPS
science, for ultimate use in NRCS field
offices.
 Two development paths for a common
model are being pursued at present –
one building a modular combined model
within OMS, the other utilizing WEPS as
the basic framework.
Questions??