Development of streambank erodibility relationships for North Carolina streams

The purpose of this study was to establish relationships between bank erodi bility and shear stress in the near-bank region with measured erosion rates . Bank erosion pins were established at 27 cross-sections throughout 7 stre am reaches in North Carolina. To estimate the general erodibility of the ba nk, the Bank Erosion Hazard Index (BEHI) and estimated shear stress in the near-bank region were calculated and classified into one of six ratings : v ery low, low, moderate, high, very high and extreme. Periodically, the site s were visited to measure pin extensions and to reevaluate the BEHI, bank p rofile and cross-sections. Annual erosion rates were extrapolated from pin extension measurements. Preliminary relationships show high variability bet ween the BEHI, estimated near-bank shear stress and the measured erosion ra tes. This may be due to the small sample size, the short time period over w hich data were collected, and the method of estimating near-bank shear stre ss. Therefore, the analysis presented here is only a beginning point for de velopment of these relationships. Future plans involve developing these rel ationships using a different method for calculating near-bank shear stress.