Investigating temporal variation of rill erosion in an erosion-susceptible soil under different rainfall intensities

Rill erosion is a major factor of soil loss in the marl formations. The marl formations are very susceptible to water erosion processes and cover a wide area in some watersheds in arid and semi-arid regions. Knowledge of temporal variation of rill erosion and its effect during a rainfall event can provide information on the mechanism of rill erosion in the hill slopes. Therefore, this study was conducted to investigate the temporal variation of flow characteristics and rill erosion in a marl soil under different simulated rainfalls. A laboratory experiment was carried out using 10 simulated rainfall intensities ranging from 10 mm h-1 to 100 mm h-1 with three replications. Soil samples were collected from the marl formations in west of Zanjan and separately purred to a flume with 4m in length and 0.94 m in width putted on 10% slope. Rill erosion and flow characteristics (discharge and concentration) were measured at 5-min from starting flow/ runoff in each rainfall intensity. Results indicated that there are substantial differences in the flow starting time, flow concentration and rill erosion among the rainfall intensities (P< 0.0001). Rill flow and erosion rapidly occurred with increasing rainfall intensity. Rill erosion increased speedily during rainfall and reached to approximately constant value in the last times (about 45 min). The flow concentration appeared also a similar trend with the rill erosion, while flow discharge showed an increasing trend in the last times. The study revealed that the threshold and pick time of rill erosion were strongly varied during rainfall. The variation trend of rill erosion during rainfall increases with increasing the rainfall intensity.