Skip to main content
ARS Home » Pacific West Area » Pullman, Washington » Northwest Sustainable Agroecosystems Research » Research » Publications at this Location » Publication #182041
Title: WEPP SIMULATION OF OBSERVED WINTER RUNOFF AND EROSION IN THE PACIFIC NORTHWEST, USA

Author
item GREER, CORY - WASHINGTON ST UNIVERSITY
item WU, JOAN - WASHINGTON ST UNIVERSITY
item PRABHAKAR, SINGH - WASINGTON ST UNIVERSITY
item McCool, Donald

Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2005
Publication Date: 2/1/2006
Citation: Greer, R.C., Wu, J.Q., Singh, P., and McCool, D.K. 2006. WEPP Simulation of Observed Winter Runoff and Erosion in the U.S. Pacific Northwest. Vadose Zone Journal 5:261-272.

Interpretive Summary: The Palouse area of the Pacific Northwest (PNW) U S A is prone to high water erosion throughout the winter. Excessive soil loss is the result of a combination of winter precipitation and snowmelt, intermittent freezing and thawing of soils, steep land slopes, and aggressive tillage-based crop management practices. Soil strength is typically decreased by the cyclic freeze and thaw, particularly during the period of thawing. Our study was aimed at improving the knowledge of winter hydrology and water erosion in the PNW through combined field experimentation and mathematical modeling. Surface runoff, sediment, and soil moisture and temperature were collected from three paired field plots under conventional tillage and no-till treatments. These data were used to assess the suitability and performance, under PNW winter conditions, of the USDA-ARS Water Erosion Prediction Project (WEPP), a physically-based erosion model. Field observations revealed that minimal erosion was generated on the no-till plots, whereas erosion from the conventionally tilled plots greatly exceeded the tolerable rates recommended by the Natural Resources Conservation Service. The WEPP model could reproduce certain winter processes (e.g., snow and thaw depths and runoff), but further modifications are needed to represent all the complicated processes of winter erosion. With continued field and laboratory investigation and further development of theory, these processes can be properly represented in WEPP. This will improve erosion modeling, conservation planning, and conservation policy development and application on over 200 million acres of winter erosion affected cropland in the USA.

Technical Abstract: The Palouse area of the Northwestern Wheat and Range Region suffers high erosion throughout the winter season. The excessive soil loss is a result of a combination of winter precipitation, intermittent freezing and thawing of soils, steep land slopes, and improper management practices. Soil strength is typically decreased by the cyclic freeze and thaw, particularly during the period of thawing. When precipitation occurs over these freeze-thaw cycles, soil is easily detached and moved downslope. This study was aimed at improving the knowledge of winter hydrology and erosion in the Pacific Northwest (PNW) through combined field experimentation and mathematical modeling. Surface runoff and sediment were collected for three paired field plots under conventional tillage and no-till, respectively. Additionally transient soil moisture and temperature at various depths were continuously monitored for two selected plots. These data were used to assess the suitability and performance of the USDA's WEPP (Water Erosion Prediction Project), a physically-based erosion model, under PNW winter conditions. Field observations revealed that minimal erosion was generated on the no-till plots, whereas erosion from the conventionally tilled plots largely exceeded the tolerable rates recommended by the Natural Resources Conservation Service. The WEPP model could reasonably reproduce certain winter processes (e.g., snow and thaw depths and runoff) after code modification and parameter adjustment. Yet it is not able to represent all the complicated processes of winter erosion as observed in the field. Continued field and laboratory investigation of dynamic winter runoff and erosion mechanisms are necessary so that these processes can be properly represented by physically-based erosion models.