Wednesday, November 15, 2006 - 10:40 AM

Sediment Contributions from River Bank Sloughing in Southern Minnesota.

Satish Gupta, Dept. of Soil Science, 1991 Upper Buford Cir U OF MN, 1991 Upper Buford Cir U OF MN, St. Paul, MN 55108, United States of America, David Thoma, National Park Service, P.O. Box 170007, Bryce Canyon, UT 84717, and Nathanael Bartholomew, University of Minnesota, 7798 Hearthside Ave S Apt 101, 7920 Hearthside Ave S Apt 219, Cottage Grove, MN 55016-4768, United States of America.

Sediment pollution is one of the major causes of surface water impairment. Presence of suspended sediments in rivers and lakes increases turbidity which limits light penetration and thus plant growth for aquatic organisms. Suspended sediments also directly affect the functioning of healthy aquatic organisms through its effects on gill functions and covered spawning areas. This paper discusses a study on characterization of sediment contributions from riverbanks and the underlined mechanisms for bank erosion. The study was conducted on the Blue Earth and the LeSueur Rivers, two major tributaries of the Minnesota River. Mass wasting contributions were characterized using the airborne LIDAR. Detailed topographic data were collected on 56 km length of the Blue Earth River in 2001 and 2002 with a helicopter mounted Topeye laser system. X,Y, Z coordinates of the laser returns were stripped of vegetation effects and then converted into two 1 m bare earth digital elevation models. Two models were differenced to calculate the volume change and then mass wasting between April 2001 and April 2002. Sediment loads were calculated as a percentage of transportable material in the river bank strata. For the Blue Earth River, 23% to 56% of the sediment mass transported past the gauging station was estimated as contributions from mass wasting. A subsequent experiment on an actively sloughing bank along the LeSueur River showed that differences in hydraulic properties of various river bank strata lead to pore water pressure build up which caused bank failure and thus mass wasting. Differences in hydraulic properties of bank strata were due to differences in particle size distribution of parent materials that were deposited as lake sediments. Movies and animations are used to show mass wasting processes, use of LIDAR data, and the linkage between landscape hydrology and mass wasting processes at the river's edge.