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 long-term 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 = R K L S C P

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 ARS-Wind 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 ARS-National 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 – Windows-based, 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 (WEPP-SPUR). 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 ARS-GPSRU in Fort Collins, CO.

2004 Project Objectives Short-term Long-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: Code reuse and sharing Capture of legacy knowledge Collaborative development Database access Verification/validation QA/QC Maintenance and change management

Components in OMS Scientific component Infrastructure component Utility component … “Components are software units that are context-independent both in the conceptual and technical domain” Well adopted methodology for software reuse Internal hidden behavior Component Input Output Well known interfaces Component

Scientific Component Represents a basic processing unit Conceptual purpose Runoff computation Soil erosion computation … Component Input Output Components are “tagged” by implementing interfaces: Native, Runable, Stateful, Visualizable Customization by implementing these interfaces: Minimum: Runable Component

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

OMS also has output graphic and parameter editing capabilities Modeling Projects Component Editor Output Analysis OMS also has output graphic and parameter editing capabilities Component Library Parameter Editor Assembled Model

OMS Workflow Summary Component Builder Model Builder Output Analysis Analyze Execute Publish Integrate Component Library 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 stand-alone 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

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 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??