ESTIMATES OF STREAMBANK EROSION IN A SURFACE MINED DISTURBED WATERSHED OF SOUTHERN APPALACHIA

Mountaintop coal mining is a debated environmental issue which has a significant influence on Appalachian watersheds, particularly their channel evolution. A major issue related to the mining is the increase in sediment load and transport from increased runoff and streambank erosion during storm events. Estimates of streambank erosion associated with surface mining are important presently because environmental regulations of mining are being reevaluated. This study uses a compartmental streambank erosion model to estimate rates of streambank erosion in an actively mined first-order watershed in Eastern Kentucky. The study site is Island Branch (2.2 km²), a subwatershed of the Line Fork Watershed located in Letcher County, Kentucky. Island Branch was reclaimed with grassland one year ago and is 8.4% disturbed. The model employed is based on the process of fluvial erosion of streambank soils. In this study, a set of equations were formulated in order to determine sediment yield for seven representative stream banks of Island Branch. The inputs to the model are bank cross sectional information as well as flow (m³/s). The output for the model is sediment yield, on the order of .04-.29 (g/cm²/s). Among the findings is that the banks furthest downstream were eroding at a rate up to five times faster than upstream banks. Variance in soil shear strength was determined to be negligible for the Island Branch watershed, and given a precipitation of 127 cm in a year, the seven studied banks would erode up to 17.9 kilograms a year. Further studies include utilizing an end-member unmixing model using δ¹³C and δ¹⁵N as tracers to determine how much eroded sediment is coming from the reclaimed grassland.