Estimating Mannings Roughness Coefficient for Shallow Overland Flow in Non-Submerged Vegetative Filter Strips

Results of an experimental study showed that overland flow in non-submerged vegetative filter strips can bedescribed by the Petryk and Bosmajians modified Mannings formula with a variable roughness coefficient. Theroughness coefficient is made up of the shear stress caused by the boundary roughness and the drag force caused by thevegetative elements. The resistance due to vegetation was related to vegetation density and flow depth. For small flowrates, the shear stress at the boundary played the major role. As the flow rate increased, the drag force due to thevegetative elements became dominant. The model can be used to estimate flow velocity in vegetative filter strips (VFS).