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Development and Application of Methodology for Determination of Hydraulic Roughness for Vegetated Floodplains

Methodology for the determination of hydraulic roughness of floodplains containing woody vegetation has been developed in collaborative research conducted by the U.S. Army Engineering Research and Development Center’s Waterways Experiment Station and Utah State University. The methodology developed through the cooperative research requires only the determination of plant stiffness and standard hydraulic geometric and flow values to determine hydraulic roughness due to shrubs and other woody vegetation. The roughness can be expressed in terms of shear velocity or Manning’s n values. The use of the equations requires a value for the stiffness modulus of the plants being evaluated. A methodology is presented to estimate a plant stiffness modulus for use in the equations developed in this study. This stiffness value can then be used in the developed equations to estimate Manning’s n values and shear velocities for shrubs and other small woody vegetation in the floodplain. This paper summarizes the development of the methodology, the research behind the methodology, and the equations that have been developed. The application of this methodology is presented in a detailed example for compound channels. This example will guide the reader / practitioner through the application of the methodology under practical conditions.