Quantifying River Bank Erosion with Lidar In Blue Earth County, Minnesota.

Suspended sediment in the Minnesota River Basin (MRB) is an important issue in the state of Minnesota.  However, research is needed to quantify the level of sediment and phosphorus contributions from river banks.  A GIS-based change detection study using two airborne LiDAR scans taken in 2005 and 2009 was undertaken to quantify sediment losses from banks along several MRB rivers in Blue Earth County, Minnesota, an area known to contribute the majority of the suspended sediment in the MRB.  The rivers analyzed included: the Blue Earth, Le Sueur, Watonwan, Maple, Big Cobb, Little Cobb rivers; Perch Creek, and the Minnesota River at the county’s northern edge.  The total volume loss from bank erosions from 2005-2009 was 1.71 million m³. The results show that banks contributed 62 and 78% of the measured total suspended solids at the mouth of the Blue Earth River and the Le Sueur River, respectively. Corresponding soluble P and total P losses were 0.17% and 42% for the Blue Earth River and 0.15% and 46% for the Le Sueur River.  Incorporating fine sediment content and bulk density values from additional data bases resulted in bank erosion contributions of 49% to 92% for fine sediments, 0.15 to 0.18% for soluble P and 42 to 49% for total P.  We conclude that river banks are the primary source of sediment within Blue Earth County and multi-temporal airborne LiDAR is a useful tool for quantifying bank erosion contribution to suspended sediment loads and associated P over large scales.