Hydraulic characteristics of varying slope gradients, rainfall intensities and litter cover on vegetated slopes

Abstract

Litter produced by forests performs crucial functions in rainfall interception and soil conservation, particularly in the condition that larger raindrops formed by canopy accelerate soil erosion. To explore how forest litter exerts runoff hydrological characteristics and sediment yield processes, experiments on forest covered (Vitexnegundo var. heterophylla) slopes were conducted under various combinations of rainfall intensities and slope gradients. The results showed that litter reduced runoff yield rate by 9-31% and reduced sediment yield rate by 65-90%, with mean runoff and sediment reductions of 18% and 76% for all treatments. On forest covered slopes, Reynolds number and runoff power generally increased with the increase in both rainfall intensity and slope gradient. Litter layer reduced Reynolds number and runoff power with 8-29% and 56-80%, respectively. Darcy-Weisbach resistance coefficient decreased by increasing rainfall intensity and slope gradient. Litter layer increased Darcy-Weisbach resistance coefficient by three to nine times. Relationships between sediment yield rate and Reynolds number, runoff power, Darcy-Weisbach resistance coefficient were described by exponential, linear, power functions, respectively. The critical runoff power values for slopes with and without litter were 0.0027 and 0.0010 m/s, respectively. Reynolds number was the best hydrodynamic parameter for dynamic erosion characterizing.