Streambank and bluff erosion modeling for the Knife River, Minnesota

The Knife River watershed on Minnesota's north shore of Lake Superior has been the focus of considerable watershed management efforts over the past several years because of concerns with high turbidity affecting its productive trout and salmon fishery. This project was undertaken to model erosion originating from banks and bluffs on 21km of the Knife River. Erosion response from three flow events in 2005 was simulated. The CONCEPTS and BEHI models were used comparatively to predict bank erosion while the SEDIMOT II model was used to predict bluff erosion. The project timeline did not allow for extensive collection of channel cross-sections and no observed erosion data was available. Uncalibrated results from CONCEPTS and BEHI show reasonable agreement with each other: CONCEPTS=344, 97, and 21 tons and BEHI=481, 82, and 16 tons of net bank erosion for storms 1, 2, and 3, respectively. Uncalibrated results from SEDIMOTII predicted 151, 51, and 23 tons of net erosion from bluffs for storms 1, 2, and 3, respectively. Factoring in estimations of tributary and overland sediment contributions with the bank and bluff erosion results, total predicted net erosion was 563, 161 and 53 tons while measured sediment mass at the watershed outlet was 881, 138 and 30 tons for storms 1, 2 and 3, respectively. This study illustrates that CONCEPTS, BEHI and SEDIMOT II implementations can still provide useful results despite using parameters estimated using GIS, aerial photo and regional hydraulic geometry analyses, supplemented by limited field data.