Study on the resistance characteristics of layered vegetation to overland flow

Different types of plants in the vegetation community near the surface of the basin coexist, forming a layered vegetation distribution with high and low plants in the morphology. In order to research the characteristics of flow resistance generated by layered vegetation on slope runoff, a flume experiment was carried out by simulating layered vegetation. The Manning roughness coefficient n was used to characterize the flow resistance of vegetation. Three kinds of vegetation with height combinations of 5 and 7 cm, 6 and 8 cm, and 7 and 9 cm were used for this experiment. By studying the relationship between Manning roughness coefficient n and water depth, it is found that the change of flow resistance of layered vegetation is closely related to the submerged state. The distribution of n shows an inverted “J” type with the increase of water depth. Under the condition of nonsubmerged state and transitional submerged state, n increases with the increase of water depth. The critical point n values of the two states will plummet, and the growth rate of n in the nonsubmerged state is greater than that in the completely submerged state. In the transitional submerged state and completely submerged state, the higher the plant height below the water surface, the higher the corresponding n value and the greater the change rate of n. Formula for predicting overland flow resistance of layered vegetation was established by considering the influence of combined vegetation height and Reynolds number.