Effect of riparian vegetation on flow resistance and flood potential

An existing hydraulic model is modified to predict stage-discharge curves for channels with nonuniform cross sections, sand and gravel-bed materials, and flexible or nonflexible riparian vegetation. The model is based on a version of the flow momentum and continuity equations that account for lateral shear. The model accounts for the effects of vegetation using empirically calibrated flow resistance equations that incorporate measurable physical properties of vegetation. Separate flow resistance equations are used for flexible and nonflexible vegetation types. Simulated stage-discharge curves are compared with data obtained from three natural river channels. Discrepancies between simulated and observed data range between 2 and 45%, but most (similar to 70%) discrepancies were <15%. Sensitivity tests are performed to determine the effects of different types of riparian vegetation on friction factor and flood elevation. Surfaces covered by nonflexible vegetation are rougher than those covered with flexible riparian vegetation. Based on simulations at the three study sites, operational maintenance regimes are proposed that minimize flood risk, while maximizing the environmental benefits of a well-developed riparian vegetation cover.