Simulation of Rainfall Intensity and Slope Gradient to Determination the Soil Runoff Coefficient at Microplot Scale

Abstract

Simulating rainfall is one of the valuable methods of measuring hydrological data and soil erosion processes. Rapid evaluation, high repeatability, and low cost are the reasons of using rain simulators. In this study, a rain simulator was constructed in dimensions of 3.0 × 3.0 × 3.0 m and it was protected on three sides by a plastic cover. An inclined table was used to create slopping surfaces of 5, 10, and 15%. Microplots were used in the dimensions of 0.2 × 0.4 × 1.0 m to collect and measure direct runoff in a bucket outside the device. Nozzles were calibrated to produce two different rainfall intensities 10 and 20 mmh−1 using sprinkler Model 5B at 8 and 12 psi, respectively. Furthermore, three different soil types, namely, clay loam (CL), silty clay (SC) loam, and SC were examined. In general, it was observed that with increasing the rainfall intensity and slope, the rate of runoff and sedimentation increase. SC soil at 15% slop offered the highest performance under the intensity of 20 mmh−1. SC and the CL soils produced the highest and lowest runoff coefficients, respectively. The CL soil produced the highest soil loss (1 kgm2 at 15% and I = 20 mmh−1). Further, it was concluded that a significant change (an average increase of 53%) in soil loss can be achieved as the rainfall intensity increased from 10 to 20 mmh−1.

Keywords

• soil erosion;
• rainfall simulator;
• raindrop diameter;
• runoff coefficient;
• sedimentation