Shear-strength determination and stream-bank instability in loess-derived alluvium, West Tennessee, USA
Andrew Simon
Abstract
The role of shear strength and bank stability in determining long-term channel morphology is addressed as part of a larger study by the US Geological Survey to quantify channel adjustments over time and space. It is well documented that following a disturbance such as dredging or straightening, degradation migrates headward along alluvial streams. Loess-derived sediments are particularly susceptible to mass failure following bed-level lowering. All stream systems studied drain to the Mississippi River from the Obion, Forked Deer, Wolf, and Hatchie River basins. The relative stability of a slope or channel bank is a function of the forces that resist mass movement versus the gravitational forces that tend to drive that slope towards failure. Trials at successively higher normal pressures produce a series of points on the Mohr-Coulomb line which, by linear regression, are used to calculate effective cohesion (c’) and the effective friction angle.