Frictional Resistance of Overland Flow on Tropical Turfed Slope

Based on the field experiments conducted on a slope consisting of cow grass (Axonopus Compressus), the study presents the frictional resistance of overland flow on the turfed slope. The rigid stems associted with cow grass deflect the water around themselves, generating a high level of turbulence. The frictional resistance in this study is presented in terms of both the Manning n and the Darcy-Weisbach friction factor f. The results show that both the density of the turf and depth of flow play an important role in affecting the frictional resistance to flow. A high-density grass plot produces high resistance to flow and vice versa. The results also show that the frictional resistance decreases for increasing flow Reynolds number through the grass. Based on analysis of the field data, a value of two-thirds is found to be appropriate for use as the exponent of flow depth in the Manning equation for shallow overland flow.