Causes of Severe Erosion in a Clayey Soil under Rainfall and Inflow Simulation

Aims Soil erosion has been known as the most important land degradation feature in the globe and is also identified as a serious environmental threat due to its onsite and offsite effects. The aims of this study were to evaluate temporal changes of sediment concentration in a soil with high clay content under erosion by rainfall and inflow as well as interpreting the reasons for their very high erosion rate. Materials & Methods This experimental study was done in the Rainfall and Erosion Simulation Laboratory of the Soil Conservation and Watershed Management Research Institute (SCWMRI). All experiments were performed at a 20% slope gradient under 55.9mm.h-1 rain intensity for 30 minutes. Four slope lengths (1, 6, 12 and 18m) were considered for erosion simulation. With regard to the 6m length of the flume, 1 and 6m lengths were simulated only under rainfall and the other two longer lengths by combining rainfall-inflow. Findings Very high concentrations up to 80, 59, 40 and 9gr.l-1 were recorded in 18, 12, 6 and 1m slope lengths, respectively. Sediment concentration increased exponentially by increasing the length of the slope that could be explained by the influence of flow velocity increase on longer slopes. The high sediment concentration could be justified by the breakdown of the soil mass during rainfall and the formation of more than 65.0% of fine aggregates in the size of silt and very fine sand. Conclusion The erodibility of clayey soil can be explained by the secondary aggregate size distribution rather than texture properties.