WATER EROSION PREDICTION PROJECT (WEPP): DEVELOPMENT HISTORY, MODEL CAPABILITIES, AND FUTURE ENHANCEMENTS D. C. Flanagan, J. E. Gilley, T. G. Franti ABSTRACT. The Water Erosion Prediction Project (WEPP) was initiated in August 1985 to develop new‐generation water erosion prediction technology for use by federal action agencies involved in soil and water conservation and environmental planning and assessment. Developed by the USDA‐ARS as a replacement for empirically based erosion prediction technologies, the WEPP model simulates many of the physical processes important in soil erosion, including infiltration, runoff, raindrop and flow detachment, sediment transport, deposition, plant growth, and residue decomposition. The WEPP project included an extensive field experimental program conducted on cropland, rangeland, and disturbed forest sites to obtain data required to parameterize and test the model. A large team effort at numerous research locations, ARS laboratories, and cooperating land‐grant universities was needed to develop this state‐of‐the‐art simulation model. WEPP project participants met frequently to coordinate their efforts. The WEPP model can be used for common hillslope applications or on small watersheds. Because it is physically based, the model has been successfully used in the evaluation of important natural resources issues throughout the U.S. and in many other countries. Upgrades to the modeling system since the 1995 DOS‐based release include Microsoft Windows operating system graphical interfaces, web‐based interfaces, and integration with Geographic Information Systems. Improvements have been made to the watershed channel and impoundment components, the CLIGEN weather generator, the daily water balance and evapotranspiration routines, and the prediction of subsurface lateral flow along low‐permeability soil layers. A combined wind and water erosion prediction system with easily accessible databases and a common interface is planned for the future. Keywords. Computer simulation, Deposition, Erosion mechanics, Erosion models, Hydrology, Runoff, Sediment, Sediment transport, Soil conservation, Soil erosion. SDA Agricultural Research Service (ARS) increasing needs of conservationists and environmental personnel and their cooperators initiated the managers. For example, USLE was only applicable to Water Erosion Prediction Project (WEPP) in detaching regions of a hillslope, and could not estimate August 1985 to produce new‐generation water sediment deposition or sediment delivery from fields to Uerosion prediction technology for use by federal action off‐site channels or streams. In addition, USLE had no agencies involved in soil and water conservation and capabilities to estimate runoff, spatial locations of soil loss on environmental planning and assessment. At that time, the soil a hillslope profile or within a small watershed, channel erosion prediction tool in widespread use was the Universal erosion, effects of impoundments, recurrence probabilities of Soil Loss Equation (USLE; Wischmeier and Smith, 1978); erosion events, or watershed sediment yield. The WEPP Gilley and Flanagan (2007) describe the events leading to the model was developed to address all of these needs, and to release of the USLE. While the USLE was used extensively serve as a replacement for empirically based erosion to predict long‐term average annual soil loss, it was a mature prediction technologies like USLE. technology that could not easily be expanded to meet the ever Development of the WEPP model involved research engineers and scientists creating model logic and code, conducting field and laboratory experiments, working on Submitted for review in March 2007 as manuscript number SW 6942; parameterization and model testing, and creating user approved for publication by the Soil & Water Division of ASABE in July interfaces and databases. During the first ten years of 2007 as a contribution to the ASABE 100th Anniversary Soil and Water development, leading up to the 1995 model release, over Invited Review Series. 35Ămeetings were held across the U.S. to coordinate project The authors are Dennis C. Flanagan, ASABE Member Engineer, activities. Field rainfall simulation experiments were Agricultural Engineer, USDA‐ARS National Soil Erosion Research Laboratory, West Lafayette, Indiana; John E. Gilley, ASABE Member conducted on over 50 experimental sites, ranging from Engineer, Agricultural Engineer, USDA‐ARS, University of Nebraska, western rangelands to eastern croplands. Four senior Lincoln, Nebraska; and Thomas G. Franti, ASABE Member Engineer, scientists have served as project leaders over the past 22 years Associate Professor, Department of Biological Systems Engineering, of WEPP development. The history of how this program was University of Nebraska, Lincoln, Nebraska. Corresponding author: Dennis C. Flanagan, USDA‐ARS NSERL, 275 S. Russell St., West managed, the soil erosion prediction technology developed, Lafayette, IN 47907‐2077; phone: 765‐494‐7748; fax: 765‐494‐5948; and the future of WEPP technology are described in this e‐mail: [email protected]. article. Transactions of the ASABE Vol. 50(5): 1603-1612 2007 American Society of Agricultural and Biological Engineers ISSN 0001-2351 1603 Table 1. Important dates and milestones for the WEPP project. April 1985 ARS scientists from across the U.S. meet at Ramada Inn in Lafayette, Indiana, for “A Workshop on Replacement of the USLE”. August 1985 Initial core team meeting convened by George R. Foster, Hydraulic Engineer and WEPP Project Leader, in West Lafayette, Indiana. January 1987 User requirements published (Foster and Lane, 1987). March 1987 Project described to top agency representatives in Washington, D.C. August 1987 Leonard J. Lane, Hydrologist, Tucson, Arizona, appointed WEPP Project Leader. 1987‐1988 Cropland field experiments conducted on 33 soils across the U.S. 1987‐1988 Rangeland field experiments conducted at 24 sites in the western U.S. August 1989 Prototype hillslope model v89 delivered to user agencies at meeting held at Ramada Inn in Lafayette, Indiana. August 1989 John M. Laflen, Agricultural Engineer and NSERL Director, West Lafayette, Indiana, appointed WEPP Project Leader. August 1989 Hillslope model documentation published (Lane and Nearing, 1989). August 1989 Compendium of cropland soil erodibility data published (Elliot et al., 1989). June 1990 WEPP project participants receive USDA Superior Service Group Award. May 1993 WEPP technical review held at University Inn in West Lafayette, Indiana. August 1995 Hillslope and watershed model (v95.7) delivered to user agencies at special SWCS Symposium in Des Moines, Iowa. August 1995 Hillslope and watershed model documentation published (Flanagan and Nearing, 1995). August 1995 User summary published (Flanagan and Livingston, 1995). April 1999 Dennis C. Flanagan, Agricultural Engineer, West Lafayette, Indiana, appointed WEPP Project Leader. May 1999 Graphical Windows interface released with WEPP model version 99.5. January 2000 Web‐based interfaces for forest roads and hillslopes released by Forest Service. March 2001 Updated WEPP model (v2001.3) released with watershed channel and impoundment improvements. April 2001 GeoWEPP ArcView extension software for use with the model released. Sept. 2004 Web‐based interface for cropland and rangeland applications released with WEPP model version 2004.7. May 2006 Updated WEPP model v2006.5 and interfaces released with enhancements for forest hydrology. PROJECT MANAGEMENT HISTORY Table 2. WEPP Core Team and subgroup meetings, 1985‐1995. Federal action agencies that manage soil and water Dates Location Attendees resources must assess the soil erosion impact of diverse land August 20‐22, 1985 West Lafayette, Indiana 12 uses ranging from cotton fields to mountain forests. To ensure November 18‐22, 1985 West Lafayette, Indiana 15 that the needs of the user agencies were adequately February 25‐27, 1986 Tucson, Arizona 23 addressed, agency representatives were active participants in July 22‐25, 1986 Ames, Iowa 31 August 19‐22, 1986[a] West Lafayette, Indiana the WEPP project from its inception. Representatives of [a] action agencies helped define user needs and provided November 3‐7, 1986 Tucson, Arizona November 18‐20, 1986 Oxford, Mississippi 30 essential background on the range of resource issues that January 26‐29, 1987[a] West Lafayette, Indiana WEPP would need to address. The time required for the March 16‐19, 1987 Silver Spring, Maryland 35 model to run and its ease of use were issues critical to the user June 8‐11, 1987[a] West Lafayette, Indiana agencies. A timeline identifying important dates and August 25‐27, 1987 Boise, Idaho 49 milestones for the WEPP project is shown in table 1. January 18‐22, 1988[a] Tucson, Arizona A core team made up of project leaders and technical February 22‐25, 1988 Kingston, Oklahoma 46 experts from across the U.S. supervised WEPP project April 11‐15, 1988[a] Tucson, Arizona management and development. The core team met regularly September 26‐29, 1988 Columbia, Missouri 65 to review progress and discuss model development and January 30 ‐ February 2, 1989 Tucson, Arizona 71 planning (table 2). Timely completion of the WEPP project April 18‐20, 1989 Lincoln, Nebraska 52 required that important issues be resolved at core team August 29‐31, 1989 Lafayette, Indiana 90 meetings. Thus, development of the meeting agenda was an November 13‐15, 1989[a] Tucson, Arizona 27 important responsibility shared jointly by the project leader January