Assessment of Critical Condition for Rill Initiation on Degraded Hillslope

Generally, the evaluation and assessment critical condition of rill formation are useful for a better understanding of soil erosion processes. The inherence characteristics of soils, which have much dynamic variations on the hill-slopes and are affected by rill formation, are the soil critical shear stress and soil erodibility factors. This study aims to assess experimental rill incision thresholds, the determined soil critical shear and soil erodibility factors on marl formation based on precipitation characteristics and different slope gradients on sensitive marl soil. The results showed that the rainfall intensity and slope steepness factors separately and together can significantly affect the distance from the point of rill initiation run-off and rill start time and soil loss values. Rainfall intensity showed more importance than the slope gradient in the point of rill formation. Rainfall intensity and slope gradient have significant effect on the rill incision point, time of runoff start and rill start and soil loss variables. The point of rills formation (slope length) decreases with an increase in slope gradient and rainfall intensity. Finally, the results revealed that the values of soil erodibility factor (Kr) and critical shear stress of marl soil are 0.0015 s m-1 and 0.267 N m-2, respectively.