WEPP

The Water Erosion Prediction Project (WEPP) Model is a physically based erosion simulation model built on the fundamentals of hydrology, plant science, hydraulics, and erosion mechanics. The model was developed by an interagency team of scientists to replace the Universal Soil Loss Equation (USLE) and has been widely used in the United States and the world. WEPP requires four inputs, i.e., climate, topography, soil, and management (vegetation); and provides various types of outputs, including water balance (surface runoff, subsurface flow, and evapotranspiration), soil detachment and deposition at points along the slope, sediment delivery, and vegetation growth. The WEPP model has been improved continuously since its public delivery in 1995, and is applicable for a variety of areas (e.g., cropland, rangeland, forestry, fisheries, and surface coal mining).

WEPP is applicable for a wide range of geographic and land-use and management conditions, and capable of predicting spatial and temporal distributions of soil detachment and deposition on an event or continuous basis at both small (hillslopes, roads, small parcels) and large (watershed) scales. Hillslope applications of the model can simulate a single profile having various distributions of soil, vegetation, and plant/management conditions. In WEPP watershed applications, multiple hillslopes, channels, and impoundments can be linked together, and runoff and sediment yield from the entire catchment predicted. The model has been parameterized for a large number of soils across the U.S. and model performance has been assessed under a wide variety of land-use and management conditions. In addition, WEPP can generate long-term daily climatic data with CLIGEN, an auxiliary climate generator. The CLIGEN database contains weather statistics from more than 2,600 weather stations in the United States. The WEPP climate database is supplemented by the PRISM database, which further refines the climatic data based on longitude, latitude, and elevation. WEPP can provide daily runoff, subsurface flow, and sediment output categorized into five particle-size classes: primary clay, primary silt, small aggregates, large aggregates, and primary sand, allowing calculation of selective sediment transport, and enrichment of the fine sediment sizes.

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