Submitted to: Remote Sensing of Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2005
Publication Date: N/A
Interpretive Summary: River bank erosion is one of the leading sources of sediment pollution in American rivers, yet it is extremely difficult to measure accurately using traditional ground surveying techniques. This research demonstrated a high tech approach to measure river bank erosion using a helicopter mounted laser survey instrument. The instrument fired a laser at the ground 7,000 times per second. Each laser shot measured the earth surface elevation at the point it hit the ground as the helicopter flew along the river corridor. In the course of a flight millions of measurements were made that were used to generate a detailed 3D computer image of the river banks. Images were made on an annual basis and were compared using computers to estimate the amount of bank erosion that occurred between helicopter flights. The annual erosion estimated from the differences in the 3D images was 40% of the sediment measured at a river gauging station. Results of this study demonstrate the capability of a new surveying technology to assess river bank erosion. By knowing the amount of sediment added to rivers from bank erosion, resource managers at federal, state and local levels could use this technology to determining allocation of resources to projects with the greatest potential to reduce sediment pollution.
Technical Abstract: Worldwide, rivers and streams are negatively impacted by sedimentation. However, there are limited techniques for characterizing the sources of sediment i.e. upland vs. river bank erosion. This research was designed to evaluate the use of airborne LIDAR for characterizing sediment and phosphorus contributions from river bank erosion. The evaluation was done on the main stem of the Blue Earth River in southern Minnesota. Detailed topographic data were collected on an annual basis in April 2001 and 2002 over a 56 km length of the river with a helicopter mounted Topeye laser system. The database included X, Y, Z coordinates of laser returns from the river valley spaced at 60 to 100 cm intervals. Uniform one meter bare earth digital elevation models were constructed by stripping vegetation laser returns and interpolation. The two models were differenced to determine volume change over time which was then converted to mass wasting by multiplying volume change with bulk density. Mass wasting rates were further converted to sediment load based on percentage of transportable material in the bank strata. The absolute accuracy of LIDAR measured elevations determined in comparison with surveyed elevations of 5 highway bridge surfaces was '2.5 cm and '8.8 cm for the 2001 and 2002 scans, respectively. Elevation errors were quasi-normally distributed. Since it was not possible to determine what factors contributed to different levels of error in the laser scan on these highway bridges, no elevation or planimetric corrections were made in the laser data before calculating mass wasting rates. The mass wasting estimates from the LIDAR surveys varied from 23 to 56% of the sediment mass transported past the downstream gauging station depending on the range of textural material that can be considered transportable once in the river. These estimates are in the range of values reported in the literature. Total P contributions due to bank erosion from the river reach were estimated at 201 t/yr.