Watershed prioritization in order to implement soil and water conservation practices

Abstract

The purpose of this study is to identify erosion-prone in the sub-watersheds of Haraz based on water and soil conservation projects using multi-criteria evaluation method and RS and GIS techniques. In this research, 16 sub-criteria data layers included rainfall erosivity, soil erodibility, land cover, land use, leaf area index, rainfall interception, soil infiltration, slope length, slope gradient, elevation, aspect, bifurcation ratio, basin circularity, length of overland flow, drainage density, drainage texture and form factor were prepared as raster layers. The Revised Universal Soil Loss Equation (RUSLE) was provisioned to predict soil loss (ton ha⁻¹ year⁻¹) using six factors. Then, sub-criteria were rated based on the soil loss amount of RUSLE map by cutting of sub-criteria maps on RUSLE map, and also original criteria (topography, morphometric, soil, vegetation cover and climate) was weighted by AHP method. The final map was prepared from the multiplication of the weight by rate and in combination with layers in ArcGIS software by the overlay index method. The results showed soil erosion risk index varies from 2.37 to 3.89 in the basin area, and average and standard deviation are 3.06 and 0.28, respectively. Finally, prioritization of sub-watersheds was done based on average weighted of 13 sub-watershed to water and soil conservation practices and was classified into three priority high, medium and low classes. Five sub-watersheds SW1, SW5, SW8, SW11 and SW3 with total area of 30.52 % had low priority, six sub-watersheds SW4, SW6, SW12, SW13, SW9 and SW7 with total area of 62 % had medium priority, and two sub-watersheds WS2 and WS10 with total area of 7.48 % had high priority. The sub-watersheds under high erosion risk require immediate plans for soil and water conservation practices.