Effect of Rainfall and Hill Slope Characteristics on Shear Stress and Rill Formation on Marl Formation (Case Study: Taleghan Basin)

Generally، the particles start moving by force of surface water flow stress which is driven by the rainfall. Rills start to appear when the erosivity of the overland flow surpasses the resistance of the soil to detachment. The expansion of the rills depends on parameters such as water shear force (flow shear stress) and soil resistance. Furthermore، shear stress required for particles detachment is a function of runoff rate، slope steepness، and hydraulic characteristics of the surface. This research aims to obtain a better understanding of the rill formation process under different rainfall and hill slope characteristics (e. g. flow shears stress and soil loss) on Gy1 Marl Formation of the Taleghan basin. To do this، two different slopes and three rainfall intensities were considered، and all experiments were undertaken in the Institute of Soil Conservation and Watershed Management. The average flow shear stress required for rill formation was determined to be between 0. 21 to 1. 38 Pa. The effect of slope، rainfall intensity factors and their interaction effect on the rill formation were statistically meaningful at a 0. 01 significance level. The distance from the top of the slope to the point of rills formation was exponentially related، and it decreased with an increase in the slope and rainfall intensity. The average of soil loss under the rainfall intensities of 10، 55 and 110 mm/h was estimated to be 0. 45، 7. 3 and 25. 6 Kg، respectively. Thus، it can be concluded that both factors individually as well as interactively affect the values of shear stress and، in turn، soil loss.