The effects of variability in bank material properties on riverbank stability: Goodwin Creek, Mississippi

Chris Parker,Andrew Simon,Colin R Thorne

doi:10.1016/j.geomorph.2008.02.007

Abstract

Bank retreat is an important area of research within fluvial geomorphology and is a land management problem of global significance. The Yazoo River Basin in Mississippi is one example of a system which is experiencing excessive erosion and bank instability. The properties of bank materials are important in controlling the stability of stream banks and past studies have found that these properties are often variable spatially. Through an investigation of bank material properties on a stretch of Goodwin Creek in the Yazoo Basin, Mississippi, this study focuses on: i) how and why effective bank material properties vary through different scales; ii) how this variation impacts on the outputs from a bank stability model; and iii) how best to appropriately represent this variability within a bank stability model. The study demonstrates the importance that the variability of effective bank material properties has on bank stability: at both the micro-scale within a site, and at the meso-scale between sites in a reach. This variability was shown to have important implications for the usage of the Bank Stability and Toe Erosion Model (BSTEM), a deterministic bank stability model that currently uses a single value to describe each bank material property. As a result, a probabilistic representation of effective bank material strength parameters is recommended as a potential solution for any bank stability model that wishes to account for the important influence of the inherent variability of soil properties.

Highlights

Bank erosion is an important erosion process in alluvial streams and is a land management problem of global significance (ASCE, 1998a; 1998b)
This study hopes to take advantage of this, and through an investigation of bank material properties on a stream in the Yazoo Basin, Mississippi, we focus on two issues; firstly, on how and why effective bank material properties vary spatially and secondly, on what impact this variability has on the output of a bank stability model
It is important to consider the results of any study in the context they were obtained (Bauer, 1996) and the specific results from this study are delimited spatially to the seven surveyed cross-sections on the Goodwin Creek Bendway, Mississippi and temporally to the 8 weeks over which they were surveyed during the summer of 2005

Summary

Introduction

Bank erosion is an important erosion process in alluvial streams and is a land management problem of global significance (ASCE, 1998a; 1998b). Conceptual models of bank retreat attempt to explain this response, describing how bank failure occurs when erosion of the bank toe and the channel bed adjacent to the bank have increased the height and the angle of the bank to the point that the gravitational forces exceed the shear strength of the bank material, resulting in mass failure (Osman and Thorne, 1988) Taking this conceptual model, the stability of river banks can be considered to be controlled by a balance between the gravitational forces acting on the steepened bank, and the resisting forces controlled by the geotechnical strength of the in situ bank material. Given this threshold condition that determines bank stability, it is important to quantify the driving and resisting forces in order to accurately define bank-stability thresholds

Objectives

Results

Conclusion