Contribution of cropland wind erosion to dam sediment accumulation in agriculturally dominated watersheds of the Northern Great Plains

Abstract

Sediment accumulation in reservoirs is a worldwide issue of concern, and particularly acute in agricultural watersheds of the midwestern United States Historical design methods used to estimate sediment storage needed over the lifespan of dams in agricultural watersheds focused on cropland sheet and rill erosion caused by the forces of water. However, research over the last two decades has considered the additional sediment contributions of cropland gully erosion, streambank erosion, urbanization, upstream impoundments, and road construction to dam sediment accumulation. Previous studies have not evaluated the contribution of cropland wind erosion to reservoir sedimentation rates. Therefore, I investigated the extent to which wind erosion generated sediment loads contribute to reservoir sedimentation in the wind erosion prone landscape of the northern Great Plains. I used measured sediment accumulation data at six northeastern North Dakota dams, in conjunction with models for sheet and rill erosion, wind erosion, and local data for streambank erosion rates, to construct a sediment budget for each dam and estimate a sediment delivery ratio for wind erosion. My results indicated that 31% to 73% of accumulated sediment volume in the reservoirs originated from wind erosion, with a median value of 46%, excluding one dam where the sheet and rill erosion model did not perform well. For the five dams a reasonable sediment budget could be computed, the sediment delivery ratio for the creep and saltation component of modeled wind erosion ranged from 0.05 to 0.31, with a median value of 0.16. I also conducted a separate evaluation of the relationship between accumulated sediment and the extent of wind protection provided by trees adjacent to cropland over the lifespan of the dams. I manually digitized extents of cropland adjacent windbreaks, shelterbelts, and forests using aerial photos from 1962, 2003, and 2020. Results of this analysis indicated an inverse relationship between cropland wind protection and sediment accumulation, providing further support for wind erosion as a sediment source to the reservoirs.