TOPOGRAPHIC EFFECT ON EROSION FROM CROPLAND IN THE NORTHWESTERN WHEATREGION

Accurate erosion prediction on rainfed cropland of the Northwestern Wh eat and Range Region has been severely hampered by lack of suitable sl ope length and steepness relationships. Relationships derived from dat a from the humid regions of the United States over-predicted the effec t of slope steepness for the steep slopes commonly cultivated in the P acific Northwest. In this 10-year field study, rill erosion data were collected from selected fields along an 80-km transect across eastern Washington and northern Idaho. Data from more than 2,100 slope segment s were used to develop new slope length and steepness relationships. T hese new relationships will significantly improve erosion prediction i n this region.