OVERLAND-FLOW IN WETLANDS - VEGETATION RESISTANCE

Emergent wetland vegetation frequently provides most of the resistance to flow of surface water. Stems are typically spaced many diameters apart. Therefore, fluid friction should be computed from drag on single objects, not channel or packed bed equations. Complication arises from vertical variation of vegetation density and nonoriented spatial variation of soil elevations. Further, flows are often in the transition region between laminar and turbulent; and the Manning equation is therefore not appropriate. A detailed approach requires knowledge of statistical distributions of wetland ground elevation, depth, and velocity. Ground slopes are typically in the range of 0.1-100 cm/km. However, the depth range is small, so the combined effects recorrelate to a simple power law equation for dense emergent vegetation with spatial uniformity on the scale of 10 m. Parameters in. the model can be estimated with sufficient accuracy from vegetation and soil surveys, combined with relatively little hydrologic data. Data from several studies are examined from this perspective. © ASCE.