Experimental Study on Slope Runoff Generation Process in North China Mountainous Area

Simulated rainfall is a valid tool to examine the runoff generation on the slope. 13 simulated rainfall experiments with different rainfall intensities and durations are completed in a 5 m×10 m experimental plot in mountainous area of North China. Simultaneously, rainfall, surface runoff, soil-layer flow, mantel-layer flow and soil moisture are monitored respectively. From the results, it is found that the runoff process in all layers has the characteristics of rapid rise and fall. The recession of surface runoff and soil-layer flow is much faster than that of mantel-layer flow. Surface runoff, the main contributor, makes up more than 60% of the total runoff in the study area. It even exceeds 90% in the case of high intensity rainfall. Runoff coefficient is mainly influenced by rainfall, rainfall intensity and initial soil moisture. Their multiple linear regression function is ?琢 = 0.002P + 0.182i + 4.88Wa - 0.821. The relation between the rainfall intensity and the lag time of surface runoff, soil-layer flow and mantel-layer flow is shown to be exponential. The result also shows that the recession constant in this area can be divided into up and down layer, surface with 0.75 and soil-layer and mantel rock with 0.94, respectively. In this study area, the dominant infiltration excess runoff is simulated by Horton model. About 0.10 mm/min percolation is observed under the condition of different rainfall intensities, therefore the value is regarded as the steady infiltration rate.