How Rainstorm Patterns Affect Hillslope Runoff and Sediment Process.

Varying rainfall intensity as rainfall events is a common phenomenon, but little information is available concerning the effects of varying-intensity rainstorms on hillslope soil erosion process. Five simulated rainstorm patterns, each with a different rainfall intensity pattern but with the same average rainfall intensity and total rainfall amount, were designed to quantify how rainstorm patterns affect hillslope runoff and sediment processes under two surface treatments. The investigated five rainstorm patterns were: the even, rising, falling, rising-falling, and falling-rising pattern. These rainstorm patterns were subjected to two surface treatments of raindrop impact being present and absent by placing nylon net over soil pans. Results showed soil loss from varying-intensity rainstorms was 1.13–5.17 times greater than that from even-intensity rainstorm and the rising pattern had the highest soil loss. Moreover, there was a wide range differences in each stage of soil loss by unit runoff among different rainstorm patterns. Regardless of raindrop impact present and absent, the temporal variation of sediment concentration demonstrated different sediment regimes among rainstorm patterns. The differences in soil loss among five rainstorm patterns were related to sediment regime and hydraulic characteristic of overland flow. The hydraulic parameter of flow velocity (V), Reynolds number (Re), Froude number (Fr) and Darcy-Weisbach coefficient (f) from varying-intensity rainstorms increased by 30%–55% and 70.01%–161.66%, respectively, relative to those from even-intensity rainstorms., The key hydraulic parameter affecting soil loss was Froude number in the presence of raindrop impact and flow velocity in the absence of raindrop impact.