Influence of vegetation lodging on the flow regime and resistance characteristic of overland flow

Vegetation lodging downstream under overland flow is a common phenomenon; it changes the characteristics of the overland flow regime and causes the resistance effect. At present, there are few studies on the hydraulic characteristics of the slope flow caused by vegetation lodging, and the problem of the flow resistance of the vegetation morphology has been neglected or simplified, which is likely to cause large deviations in overland flow forecast. To clarify the effect of vegetation lodging on overland flow, under the conditions of slope (0.0%–3.0%) and flow discharge (0.0005–0.008 m3/s), an indoor flume experiment of vegetation gradient lodging combination and lodging angle was carried out, and the resistance mechanism and flow regime characteristics were compared and discussed. The results show that it is reasonable to use a uniform lodging angle to simulate the influence of gradient lodging on the overland flow resistance. The slope and vegetation lodging states are important factors that affect the evolution of flow patterns and turbulence changes. It was found that, as the slope or degree of vegetation lodging increased, the flow patterns evolved from slow to rapid. Under the same flow discharge, the resistance of overland flow decreased with an increase in the vegetation lodging angle. Under unsubmerged conditions, the resistance coefficient f was found to be positively correlated with the Reynolds number Re and the cosine of the lodging angle θ, and negatively correlated with the slope S. Compared with vertical vegetation, the morphological resistance of vegetation with lodging angles of 20°, 40°, 60°, and 80° decreased by 10.28%, 32.53%, 52.45%, and 61.37%, respectively. The morphology of vegetation lodging is the main influencing factor that constitutes flow resistance and controls hydraulic erosion. This study provides a theoretical basis for the prediction of overland flow and soil erosion control. To clarify the effect of vegetation lodging on overland flow, an indoor flume experiment of vegetation gradient lodging combination and lodging angle was carried out. The results show that it is reasonable to use a uniform lodging angle to simulate the influence of gradient lodging on the overland flow resistance. The influence of vegetation lodging angle on flow state changes and resistance mechanism is studied, and a calculation model of resistance coefficient of lodging vegetation in non‐submerged state is established.