Experimental study on rill evolution process and runoff-sediment relationship for gentle slope

In this paper, the indoor simulated rainfall experiment with pure water was conducted to study rill evolution process and relationship between runoff and sediment for Yangling soil and Ansai soil under the fixed slope gradient (10°) and two rainfall intensities (1.5 mm/min, 2.0 mm/min). Results showed that rill was evolved from a series of step-down floor which were parallel to each other and distributed with line at slope surface direction. Yangling soil produced the rill with a small rainfall intensity, and Aasai soil produced the rill only with larger rainfall intensity. The change rule of sediment concentration and erosion rate and the moment of forming step-down floor and rill have good consistency, and the increasing rainfall intensity has little influence on sediment concentration and erosion rate for Yangling soil, however, sediment concentration and erosion rate for Aasai soil could increase rapidly and exceed Yangling soil with the emergence of rill when the rainfall intensity was larger. For Yangling soil, the rill could not cause obvious change of sediment concentration and erosion rate, however, for Ansai soil, rill formation could result in a sharp increase of sediment concentration and erosion amount.