Incorporating hydraulic roughness equations for riparian vegetation into HEC-RAS 1D: an application of the San Joaquin River reach, CA

3:20 - 4:20



To quantify the flow resistance for riparian vegetation of channels and floodplains, a large number of equations have been proposed in the past half century based on theoretical derivation or lab experiments. However, only few of them were applied to one-dimensional (1D) numerical modeling of river hydraulics and sediment transport. In this study, eleven methods to compute vegetation-induced roughness were gathered from the literature. The change of Manning’s n for vegetation with the increase of flow depth from zero to threefold of plant height was calculated and compared among these methods to check the feasibility of adding them into hydraulic model. Next, all the methods were incorporated into a 1D hydraulic model HEC-RAS to automatically compute dynamic Manning’s n for vegetation based on vegetation properties and flow conditions instead of using user-defined values. The enhanced HEC-RAS was applied to a reach of the San Joaquin River to compute spatially explicit and temporally dynamic roughness coefficients under six flow conditions using vegetation data from field survey and GIS vegetation mapping. The HEC-RAS model of this reach was calibrated with observed river stage profiles and hydrograph in 2011, and validated with observed hydrograph in 2017.

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