Secondary current effects on cohesive river bank erosion

Abstract

The emphasis of this research was placed on the development of a methodology that allows (1) an adequate representation of the distribution of the near-bank shear stress τs when secondary currents are present and (2) estimation of the critical erosional strength τcr and other sediment erodibility parameters for fluvial erosion. These two factors combine to form the overarching objective of this investigation, which was carried out in Union Flat Creek, a stream with pronounced cross-sectional irregularities located within the loess region of the Palouse basin of Washington State, United States. The study has shown that the presence of the secondary currents increases the magnitude of the depth-averaged sidewall shear stress at least by a factor of 2.0. It was also found that the ratio of the maximum to the depth-averaged sidewall shear stress equation image is greater than 5. These findings suggest therefore that use of the equation image may be a good approximation of the fluid shear stress magnitude for simple channel geometries but not for natural channels characterized by complex geometries. The measured critical erosional strength (τcr = 4.16 Pa) was comparable with the findings of other laboratory and field studies that also focused on Palouse sediments.