Modeling the Evolution of Incised Streams. II: Streambank Erosion

Abstract

Incision and ensuing widening of alluvial stream channels is widespread in the midsouth and midwestern United States and represents an important form of channel adjustment. Streambanks have been found to contribute as much as 80% of the total suspended load. The location, timing, and magnitude of streambank erosion are difficult to predict. Results from field studies to characterize the resistance of fine-grained materials to hydraulic and geotechnical erosion, the impact of pore-water pressures on failure dimensions and shearing resistance, and the role of riparian vegetation on matric suction, streambank permeability, and shearing resistance are used to enhance the channel evolution model CONCEPTS (conservational channel evolution and pollutant transport system). This paper discusses the conceptualization of the above-mentioned physical processes, and demonstrates the ability of the derived model to simulate streambank-failure processes. The model is tested against observed streambank erosion of a bendway on Goodwin Creek, Miss. between March 1996 and March 2001, where it accurately predicts the rate of retreat of the outside bank of the bendway. The observed change in average channel width within the central section of the bendway is 2.96m over the simulation period, whereas a retreat of 3.18m (7.4% larger) is simulated. The observed top-bank retreat within the central section of the bendway is 3.54m over the simulation period, whereas a retreat of 3.01m (15% smaller) is simulated.