Modeling stream-bank erosion in the Southern Blue Ridge Mountains

Abstract

Deforestation, followed by soil erosion and subsequent deposition of alluvium in valleys, played a critical role in the formation of historical terraces in much of the Southern Blue Ridge Mountains. Such terraces add a significant amount of sediment to the tributaries of the region as streams laterally erode the terrace banks. This study examined the contribution of total sediment yield derived solely from eroded stream banks in small watersheds (<20 km²), using floodplain widths as proxies for long-term lateral erosion rates. The raw data were derived from watersheds with different land covers (Coweeta Creek and Skeenah Creek watersheds in the Upper Little Tennessee River basin). Bank-derived sediment yield estimates were modeled in a Geographic Information System, using linear regression to relate floodplain widths and erodible terrace bank heights. We found total stream length to be a good predictor of both lateral erosion rates and erodible bank heights. Land cover, basin/ network morphometrics, and reach-scale stream conditions were not good predictors. Modeled lateral migration and sediment yield results compare favorably to empirical measurements from five independent watersheds in the region. Modeled estimates fall within ±50% or better of the observed values, at 16.33 to 25.02 t km −2 yr −1 .

Historical erosion and sedimentation in two small watersheds of the southern Blue Ridge Mountains, North Carolina, USA

“…The notion of the aggradation-degradation episode (James and Lecce, 2013), here described for the southern Piedmont, should be generally applicable to a wide range of humid-climate environments, including the adjacent Blue Ridge Mountains, where locally, highly erosive historical land uses have given way to reestablishment of vegetation cover, limiting new sediment production. Indeed, Leigh (2010) and Rogers and Leigh (2013) have recently documented the occurrence of well-developed historical sediment terraces in parts of the southwestern Blue Ridge. The details of sediment dynamics including the pathways, types, and rates of sediment movement, as well as exact quantities and locations of sources and sinks are also important for effective and spatially explicit environmental management.…”