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Effects of Vegetation on Hydraulic Roughness and Sedimentation in Wetlands

Abstract : This technical note summarizes available literature and experimental findings to date on the effect of dense wetland vegetation on sedimentation in wetland environments. Sedimentation processes in wetlands include erosion, deposition, and transport of sediments within and through the boundaries of the wetland. Sedimentation tests conducted on a dense stand of bulrushes (sciqw VUZidus)indicate that sediment deposition rates may be lower than anticipated when using average velocities in sediment transport equations. The calculation of Manning n values has been of interest since the Manning equation was presented in the late 1800s (Henderson, 1966). While estimation of n vahm for normal channels has been fairly well standardized, the estimation of n values in areas of dense vegetation continues to be subject to large variations depending on the experience of the engineer and the perceived density of the vegetation. Flow resistance and sedimentation in bulrush environments is important in design of constructed wetlands, flood routing through existing wetlands, and determination of flood heights for flood damage studies.