Evaluating the effect of different methods for calculating topographic factor on sediment delivery rate based on RUSLE model (Case study: Barajin catchment, Qazvin)

One of the most widely used method for estimation of erosion over the catchment and the sediment delivery from the catchment is revised universal soil loss equation (RUSLE). Several studies have been carried on the importance of topographic factor (LS) which includes slope steepness and slope length factors. Over the past decades, different methods have been developed for calculation of topographic factor and hence, choosing the best one is a confusing and challenging issue. Moreover, by increasing of geographic information system (GIS) application in hydrological modeling, mathematical calculations on grid-based datasets can easily be done in GIS environ. Due to depending on grid-based datasets, RUSLE model is influenced by several factors which among them, the effect of DEM resolution and the method of LS estimation are the most important ones. This research addresses the effects of all important factors on sediment delivery load at the outlet of the Barajin catchment by coupling RUSLE model and GIS environ. Also, in order to evaluate the efficiency of this model, mean annual sediment delivery load is calculated by analyzing discharge-sediment curve and observed data at Barajin hydrometric station between 1987 and 2015. Findings show that using different methods for estimation of LS factor without considering their limitations leads to a significant relative error (RE) in the calculation of sediment delivery load. Furthermore, McCool et al equation, due to a RE of lower than 10% in estimating the sediment delivery load, is the best method for calculation of LS factor.