Defining Slope Length and Steepness (LS) Factor of the Rusle to Model Soil Erosion in Urban Mountainous Landscapes.

Intensive agriculture in mountainous landscapes can cause high soil erosion with negative impacts on farm productivity and sustainability. Occurrence of high intense rainfalls in recent years has triggered the erosion rates. The Revised Universal Soil Loss Equation (RUSLE) is an empirical equation used to estimate soil loss in relatively flat agricultural fields. Limitations of the slope length and steepness factor (LS factor) decreases the applicability of the equation to more complex landscapes where the water is the major soil erosion agent. Various model modifications have been initiated in the recent past with the objective of obtaining reliable estimates for the LS factor. Nevertheless, problems in validating through ground-truthing of these model modifications hinder the applicability.  To address this research gap, an experiment was initiated using a PYTHON script and a R code. The PYTHON script was used to identify the water flow pathways while the R code was used to estimate and compare the L and S factors for two GIS parcel data sets (Sub-catchment (large scale) and land cover (small scale)) in three small watersheds of the Piedmont region of South Carolina. The simulated slope lengths and the slope angels were ground-truthed to validate the adopted methodology for LS factor calculation. Results revealed that the majority of the estimated slope lengths based on the land cover falls within the RUSLE restrictions (≤ 122 m). In contrast majority of the slope lengths based on the sub catchments exceeded the RUSLE restrictions. The estimated soil erosion rates under this scale was low compared to sub catchment scale. Interestingly, there was a significant relationship between the measured and the simulated slope lengths. The outcomes of this project can be utilize to determine the appropriate parcel size to calculate the reliable L and S factor values. 

Key words: RUSLE, LS factor