A Combined Analytical and Empirical Approach for Design of Stable Channel Width in Channels Having Vegetative Influences

Abstract

Channel width is a key parameter when choosing a stable channel geometry for restoration or rehabilitation of river corridors. A variety of tools are available to aid the designer in selecting a channel width. Three common methods to determine channel width are to emulate the geometry of a suitable reference reach, utilize existing hydraulic geometry relationships, or select a width based on an analytical approach. This paper presents an approach that synthesizes these methods. The approach presented identifies the limitations and inherent bias that each of the above methods pose, and attempts to merge the empirical approach with one having a more theoretical basis. The hydraulic geometry relationships are derived from years of empirical research. Research suggests, however, that the general trends described by these equations may not be applied directly to many situations, particularly at varying spatial scales. Additionally, channel width is greatly influenced by the composition of bank material and the density and composition of vegetation. These influences result in a wide range of values that may be used in the hydraulic geometry equations. Values of width that are determined using an extremal hypothesis approach typically predict stable channel widths that are narrower than seen in naturally stable, gravel bed channels. Therefore, a design approach that has an analytical basis, yet incorporates empirical relationships that account for heterogeneous bank and vegetative conditions is a valuable tool for use in the stable channel design of a river system.