Quantifying River Bank Erosion with Scanning Laser Altimetry

Detailed topographic data collected with an airborne laser scanner can help determine the extent of bank erosion and identify banks that are more vulnerable to bank collapse and thus require stabilization efforts. The Minnesota River which flows through a 95% agricultural watershed has been ranked among the top 20 most polluted rivers in the U.S. Greater than 50% of the sediment load carried by the river at Mankato, MN is delivered by a single tributary, the Blue Earth River. A 56km length of the main stem of the Blue Earth River corridor was scanned April 2001 with an helicopter mounted Topeye laser system. The database includes X, Y, Z coordinates of laser returns from the river valley plus return intensity. Other data collection included ground elevation measurements for two banks using a total station, and vegetation density at eight locations along the river. A bare earth model was constructed by removing returns from vegetation and is currently being tested against the ground elevation measurements. Plans are to make another scan in a year or more to calculate volumetric change in the river valley due to bank erosion / bank collapse. This volume change along with soil bulk density along the river corridor will be used to assess the extent of bank erosion. The mass wasting rates will then be converted to total suspended sediments assuming fine silt and clay fractions are most likely to be transported.