TOPOGRAPHIC EFFECT ON EROSION FROM CROPLAND IN THE NORTHWESTERN WHEATREGION

Accurate erosion prediction on rain fed cropland of the Northwestern W heat and Range Region has been severely hampered by lack of suitable s lope length and steepness relationships. Relationships derived from da ta from the humid regions of the United States over-predicted the effe ct of slope steepness for the steep slopes commonly cultivated in the Pacific 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 segme nts were used to develop new slope length and steepness relationships. These new relationships will significantly improve erosion prediction in this region.