Tuesday, November 14, 2006

Assessment of Streambanks: Sediment Contributions to Impaired Water Body in Eastern Nebraska.

Nathan Mueller, Univ of Nebraska-Lincoln, Dept of Agronomy and Horticulture, 279 Plant Science, Lincoln, NE 68583-0915

Streambank erosion contributes to sediment and phosphorus loading of water bodies. Few studies have been done in eastern Nebraska to evaluate the extent of that contribution to impaired water bodies, such as in Wagon Train Lake.  The pollutant reduction target has not been met even after implementation of BMPs throughout most of the Wagon Train watershed.  The objectives of this research are 1) to quantify sediment and phosphorus loads from streambanks, 2) to examine dominant mechanism(s) of streambank erosion, and 3) to determine site-specific factors controlling bank erosion in the watershed.  Data of the stream reach network were generated using GIS-interface of the AnnAGNPS Model.  Stream reaches were then stratified by drainage area.  From each stratum, four stream reaches were selected for detailed streambank observation.  Erosion pins were installed in grids with minimum disturbance to the bank.  The grids have three to nine columns with 50 cm spacing with a total amount of pins ranging from 36 to 66 per site.  Grid row spacing height was set at 20 cm to achieve adequate spatial coverage at each bank.  Site-specific factors such as bank angle, vegetation cover, bank height, and other factors are being assessed.  Soil test results revealed high levels of Bray-P1 in the soil of streambanks throughout the watershed.  Current erosion pin data suggest that falling soil crumbs from subaerial processes causes more soil loss from the streambanks than does fluvial erosion.