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ARS Home » Pacific West Area » Pullman, Washington » Northwest Sustainable Agroecosystems Research » Research » Publications at this Location » Publication #96433
Title: EVALUATION OF WEPP FOR TEMPORALLY FROZEN SOIL

Author
item McCool, Donald
item PANNKUK, C - WASHINGTON STATE UNIV.
item LIN, C - WASHINGTON STATE UNIV.
item Laflen, John

Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Proceedings
Publication Acceptance Date: 2/6/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Much of the water erosion from cropland in the Pacific Northwest is caused by runoff from winter rainfall and snowmelt. In order to understand and predict this process more accurately for designing and selecting environmentally acceptable crop management systems, erosion models such as the USDA-Water Prediction Project (WEPP) model include winter erosion components. In this study, WEPP results were compared with seven years of runoff and soil loss data from plots at the Palouse Conservation Field Station near Pullman, Washington. Using the WEPP internal default parameters, very few events were predicted for any treatment, and predicted runoff and soil loss values were much lower than observed. In-depth review of the relationships and routines for computing runoff as well as soil loss under winter conditions is in progress and will improve performance of the winter erosion component in WEPP.

Technical Abstract: Most erosion on non-irrigated cropland of the Northwest Wheat and Range Region (NWRR) of the U.S.A. results from runoff from winter rainfall and snowmelt, and frequently involves thawing soil. Runoff and erosion on cropland of the NWRR are particularly difficult to model because of the frequent freeze/thaw cycles each winter. During thaw, the soil is very weak and will erode with very small amounts of rainfall or snowmelt. The USDA-Water Prediction Project (WEPP) is a daily time-step mode capable of estimating spatial and temporal distributions of soil loss. WEPP includes winter routines developed specifically for areas where soil freezing and thawing affects runoff and erosion. Performance of the WEPP winter routines was tested with seven years of data collected from runoff plots with various crop managements at the Palouse Conservation Field Station near Pullman, WA. WEPP underpredicted the number of events as well as the runoff and soil loss. A sensitivity analysis was conducted to isolate problem areas in the model. In-depth review of relationships and routines for computing runoff as well as soil loss is in progress.