Using HEC-RAS Hydraulic Design Functions for Geomorphic Channel Design and Analysis

The Copeland method for designing geomorphologically stable channels has been included in the Army Corps of Engineers' Hydraulic Engineering Circular River Analysis System (HEC-RAS). This method requires the bottom width, depth, and side slopes of a representative cross-section from a stable, upstream reach as input. This assumes the upstream cross-section can be approximated by a trapezoidal channel, but no instruction on how to derive this trapezoidal approximation is given in available literature. Additionally, the method requires a side-slope Manning `n' value, for which the available documentation provides only qualitative guidance. This paper presents a step-by-step design example for using the Copeland method, including approximating the upstream channel as a trapezoid and calculating the sidewall Manning `n'.