Estimation of Erosion and Sediment Delivery Ratio in the Pepe River Sub-Watershed Area, Boyolali Regency using the USLE Method at BPDAS Solo

Abstract

Watersheds integrate hydrological, soil, topographic, and land-use processes that determine erosion and sediment delivery. This study estimated annual soil loss, erosion hazard level, and Sediment Delivery Ratio (SDR) in the Pepe Sub-watershed, a tropical catchment within the Upper Bengawan Solo watershed system, using ArcGIS-based spatial analysis, the Universal Soil Loss Equation (USLE), and Boyce SDR estimation. Secondary spatial data from BPDAS Solo, rainfall records for 2015-2024, and thematic maps of soil type, slope, and land use/land cover were analyzed. The mean erosion rate was 57.32 t ha-1 yr-1, while the moderate, severe, and very severe erosion classes exceeded the tolerable soil loss threshold (EDP = 40 t ha-1 yr-1). The severe and very severe classes had class erosion rates of 288.39 and 634.63 t ha-1 yr-1, respectively; however, their mapped area should be quantified from the final TBE raster attribute table before publication. The SDR value of 0.0187 indicates that approximately 1.87% of gross erosion is delivered to the outlet, resulting in an estimated sediment yield of 33,936.18 t yr-1. These findings inform SDG 6.6, SDG 11.5, SDG 13.1, and SDG 15.3 by supporting erosion control, sediment reduction, and land-degradation mitigation in tropical watershed planning.

Contribution to Sustainable Development Goals (SDGs):
SDG 6: Clean Water and Sanitation
SDG 11: Sustainable Cities and Communities
SDG 13: Climate Action 
SDG 15: Life on Land