GIS-BASED ASSESSMENT OF THE PHYSICAL EROSION SUSCEPTIBILITY USING RAINFALL EROSIVITY (R) AND TOPOGRAPHIC FACTOR (LS): CASE OF THE SILIANA RIVER WATERSHED, NORTH-WESTERN TUNISIA

Abstract

This study analyzes the spatial variability of rainfall erosivity (R factor), the topographic factor (LS), and their interaction in the Siliana river watershed, located in northwestern Tunisia, using a GIS-based integrated approach. The R factor was estimated from multi-year rainfall data covering the period 1990–2022, applying Arnoldus’ index and spatial interpolation via kriging. The LS factor was derived from a 30 m resolution SRTM digital elevation model, incorporating slope and slope length. The spatial combination of R and LS factors allowed for the assessment of water erosion potential at the watershed scale. Results show that annual precipitation ranges from 417 to 523 mm, with higher values in the mountainous areas of Bargou and Makthar. Rainfall erosivity exhibits moderate spatial variability, dominated by low to medium classes over most of the watershed. In contrast, the LS factor displays strong spatial heterogeneity, controlled by the relief morphology, with high values concentrated in the mountainous sectors of Kesra, Bargou and Makthar. The LS × R map reveals a highly contrasted erosion potential, with values ranging from 0 to 2069. High to very high risks dominate the upstream areas, whereas agricultural plains show generally low risk. These results highlight the amplifying role of topography and provide a valuable basis for soil conservation planning and sustainable watershed management.