Determining Resistance of Woody Vegetation and Shrubs in Floodplains

Previous research on channel resistance has been conducted to determine resistance due to grasses, agricultural crops, dense layered grasses and the rigid blockage of cylindrical tree trunks. However, little has been studied on the resistance effects of plants and shrubs that deform with flow and are either submerged or partially submerged by turbulent flows. The flexible stems and varying shapes of a plant leaf mass greatly complicate the understanding of resistance. The deformation of plant shape with flow precludes the use of a constant blockage or plant density in predicting resistance.

This study then considers the effects on channel resistance for the variables of plant type, plant geometry, plant density, plant flexibility, and submerged and partially submerged plants.



The purpose of this study was to investigate the effect of vegetation, particularly ground cover plants and shrubs, on flow resistance. Resistance experiments (over 220 experiments with 27 different plant types and combinations) were conducted at the Utah Water Research Laboratory utilizing a large wide flume and a smaller sectional flume. Field measurements were later conducted to obtain additional data on plant properties. Variables in the experiments included: plant types, single stem and multiple stem plants, combinations of different plant types and sizes, flow velocity, flow depth, plant geometry, drag force, plant density and spacing, plant distortion and bending, and the effect of dormant plants without leaves.





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