Functional Relationships of Resistance in Wide Flood Plains with Rigid Unsubmerged Vegetation

Abstract

The effect of rigid, unsubmerged vegetation on flow resistance in wide flood plains was examined in this study. A series of experiments was run using rigid rods inserted into the flow field of a wide shallow flume. Several configurations of rod diameters with various lateral and longitudinal spacing were tested over a range of discharge values. Head losses across the rods were measured and a resistance-to-momentum-absorbing area concept was employed to relate density parameters to the resistance coefficient. The effects of flow depth, velocity, rod diameter (d), lateral spacing (r), and longitudinal spacing (l) were estimated. The results demonstrated that flow resistance is greatly impacted by both depth and velocity but that the effects are opposite in sign. The friction factor increased in only a slightly nonlinear fashion with depth, but it decreased in a highly nonlinear manner with increasing velocity, and the velocity effects were very sensitive to vegetation density parameters. Of the density parameters tested, the effects of diameter and lateral spacing were far more significant than are those of longitudinal spacing. The results also demonstrated that the effects of all parameters (density and depth) could be effectively combined into one relative density ratio (total vegetation stomatal area/bed cross sectional area) that was linearly related to the Darcy f and the Manning n.