Comparative analysis of the effect of different algorithms for calculating the topographic factor on the amount and spatial distribution of soil erosion in the Shazand Watershed, Iran

Soil erosion is an important subject in water and soil conservation researches which is influenced by natural and anthropogenic factors. Hence, knowledge on soil erosion amount enables the identification of critical areas and prioritization of measures. One of the effective factors in the evaluation of soil erosion is slope and length (LS) which could be calculated using different methods and algorithms, so the selection of the best method to provide proper estimation is important. However, the comparison of the performance of the different estimation methods has not been sufficiently considered. Therefore, the present study was conducted to calculate the LS factor and evaluate its effect on estimations of soil erosion in the Shazand Watershed using four common algorithms viz. Renard et al. (1997); Desmet and Govers (1996); Moore et al., 1991, and Böhner and Selige (2006) in geographical information system. The results of this study while confirming the difference of about 15 times among performances of various algorithms, indicated that the mean soil erosion using the algorithm of Renard et al. (1997); Desmet and Govers (1996); Moore et al. (1991), and Böhner and Selige (2006) were 4.95, 19.47, 1.73, 1.34 t ha-1 yr-1 in case of the stability of other factors of RUSLE model. Considering the calculated amounts of slope length on the topographic map, the Desmet and Govers (1996) algorithm performed better than other algorithms in LS calculation for the study watershed. It clearly verified the necessity of selecting pertinent procedures for the calculation of input factors for the precise estimation of soil erosion.