Prediksi Laju Sedimen Menggunakan Model Soil and Water Assessment Tool Pada Daerah Aliran Sungai Karajae

AVELINE GIOVANNI. Sediment Rate Prediction Using the Soil and Water Assessment Tool Model in the Karajae River Basin. (Supervised by Usman Arsyad and Rezki Amaliah). Background. River water plays an important role in meeting domestic, agricultural, and industrial needs, but its function is threatened by sedimentation processes that reduce water storage capacity and quality. Sedimentation originating from erosion in the upstream watershed area can cause river siltation, increased flood risk, and environmental degradation. The Karajae watershed in Parepare City and Sidenreng Rappang Regency (±9,317.57 ha) is under pressure due to changes in land use and high rainfall that increase runoff and sediment load. Objectives. The purpose of this study was to analyze the sedimentation rate and its spatial distribution in the Karajae watershed. Methods. This study used primary data in the form of watershed characteristics, land cover from Sentinel-2A image interpretation, and physical and chemical properties of the soil, and secondary data in the form of slope classes, soil types, and daily climate data. The analysis was carried out using the SWAT model through the stages of watershed delineation, HRU formation, climate data processing, and simulation to predict sedimentation rates which were then classified based on sediment production levels (tons/ha/year). Results. The delineation results show that the Karajae Watershed is divided into 32 subbasins and 1,241 HRUs, reflecting the biophysical heterogeneity of the region, with a dominant surface flow of 512.31 mm/year and a Curve Number value of 81.01 indicating moderate to low infiltration. SWAT simulations show that the highest value was in 2013 (145.13 tons/year), and the lowest value occurred in 2016 at 28.87 tons/ha/year. Conclusion. The sedimentation rate in the Karajae Watershed is categorized as very high. The high sedimentation rate is influenced by rainfall, surface flow, steep slopes, land cover in the form of savanna/grassland, and the texture of dusty clay, dusty clay, and sand that have low cohesion so they are easily eroded. Therefore, watershed management is needed through soil conservation and increasing vegetation cover to reduce the sedimentation rate in the Karajae Watershed.