The Relationships of Streambank Angles and Shapes to Streambank Erosion Rates in the Little River Watershed, TN

Sediment is a leading cause of water quality impairment throughout the United States. In the Little River watershed in eastern Tennessee, several tributaries have been classified as impaired due primarily to sedimentation. Researchers at The University of Tennessee, in collaboration with a group of local and state organizations, began monitoring Little River tributaries to better understand their sources of pollution. To investigate the rates and processes of streambank erosion, erosion-pin monitoring sites were established on 32 banks in the watershed. This thesis complements the erosion-pin monitoring efforts by determining bank characteristics and examining the relationships of streambank angles and shapes to observed erosion rates. The specific objectives of this study were to: (1) characterize streambank angles, (2) describe the relationships between streambank angles and bank erosion rates, (3) characterize bank shape, and (4) determine if bank shapes at erosion-pin monitoring sites are representative of their immediate stream reaches.

Streambank angles were measured at erosion pins. Bank angles averaged approximately 55° and varied significantly between tributaries and individual monitoring sites. Bank angle measurements were compared to erosion-pin exposure using correlation analysis. Data were then sorted into subgroups by pin position, soil texture, and bank shape, and further analyses were conducted. Results indicated streambank erosion was significantly, positively associated with bank angle for angles ≥ 30°. Significant, positive relationships were also found low on banks, where soil texture was clay, and where banks were classified as undercut.

Bank profiles were documented to classify the bank shapes of erosion-pin monitoring sites and assess how well the banks at those sites represented the immediate reach. In the Little River watershed, bank profile shapes vary, but nearly three-fourths of all documented bank profiles were steeply sloping or undercut. The majority of monitoring sites (78%) were representative of the immediate stream reach with regard to bank shape. However, other factors, including surrounding land use and soil type, may differ within the immediate reach. Thus, data extrapolation from erosion pins to the reach scale should be done cautiously and take into consideration variability of individual site characteristics.