Modeling of the effect of rock fragment cover and sizes on the sediment concentration using response surface method

Surface rock fragment is one of the most important factors controlling soil erosion especially in hillslopes of arid and semiarid regions where, modeling of its effects on soil erosion has a great complexity. This study aims to model the interactive effects of surface runoff, rock fragment cover and rock fragments size on the sediment concentration using the response surface method according to the central composite design. Two sets of experiments were carried out on a fixed bed slope of 5 percent. The first set of experiments used to develop the predictive model based on central composite design and the second set of the experiments were applied to validate the model. The results of first data set indicated the high efficiency (R2= 0.934 and RMSE=1.6 gl-1) of the predictive model of sediment concentration. The model validation with the second set of data also indicated a good agreement (R2= 0.895 and RMSE=3.6 gl-1) between the predicted values of sediment concentration and the experimental values with a wide range of independent variables. From the modeling approach and experimental data it could be concluded that the sediment concentration decreases as the rock fragment cover at the soil surface increases in the range of 0 to 45 percent. However the efficiency of the small rock fragments in decreasing the sediment concentration is higher than the coarse rock fragments.