Overland Flow in Wetlands: Vegetation Resistance

TLDR

Summarize field context: emergent wetland vegetation provides resistance, stems spaced many diameters apart, fluid friction from drag on single objects, complications from vertical variation, nonoriented spatial variation, flows in transition laminar/turbulent, Manning not appropriate. Also ground slopes 0.1-100 cm/km. So background: emergent wetland vegetation is main resistance; stems spaced far; friction should be drag on single objects; complications from vertical density variation, soil elevation variation; flows often transition laminar-turbulent; Manning not suitable; ground slopes typical 0.1-100 cm/km.

Abstract

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.