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)personnel and their cooperators initiated the Water Erosion Prediction Project (WEPP) in August 1985 to produce new‐generation watererosion prediction technology for use by federal action agencies involved in soil and water conservation and environmental planning and assessment. At that time, the soil erosion prediction tool in widespread use was the Universal Soil Loss Equation (USLE; Wischmeier and Smith, 1978); Gilley and Flanagan (2007) describe the events leading to the release of the USLE. While the USLE was used extensively to predict long‐term average annual soil loss, it was a mature technology that could not easily be expanded to meet the everincreasing needs of conservationists and environmentalmanagers. For example, USLE was only applicable to detaching regions of a hillslope, and could not estimate sediment deposition or sediment delivery from fields to off‐site channels or streams. In addition, USLE had no capabilities to estimate runoff, spatial locations of soil loss on a hillslope profile or within a small watershed, channel erosion, effects of impoundments, recurrence probabilities of erosion events, or watershed sediment yield. The WEPP model was developed to address all of these needs, and to serve as a replacement for empirically based erosion prediction technologies like USLE.Development of the WEPP model involved research engineers and scientists creating model logic and code, conducting field and laboratory experiments, working on parameterization and model testing, and creating user interfaces and databases. During the first ten years of development, leading up to the 1995 model release, over 35 meetings were held across the U.S. to coordinate project activities. Field rainfall simulation experiments were conducted on over 50 experimental sites, ranging from western rangelands to eastern croplands. Four senior scientists have served as project leaders over the past 22 years of WEPP development. The history of how this program was managed, the soil erosion prediction technology developed, and the future of WEPP technology are described in this article.
PROJECT MANAGEMENT HISTORY
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