Sedimentation analysis using SWAT model (soil and water assessment tool) in Mamasa Sub-Watershed

Abstract

Soil fertility and quality of agricultural land have decreased due to erosion and sedimentation in the sub-watershed upstream area. This decrease in soil fertility is due to the loss of NPK nutrients in the topsoil. Erosion and sedimentation in the upstream area of the Mamasa Sub-watershed are caused by land degradation and forest conversion due to land expansion and shifting cultivation for cocoa, corn, and coffee. This study aimed to determine the amount of sediment in the Mamasa Sub-watershed in the Mamasa Regency by using the SWAT model. This research was conducted in the Mamasa Sub-watershed from June to September 2022 through several stages in the form of literature study, primary and secondary data collection. Then proceed with laboratory analysis, making a base map for the data analysis process. SWAT requires input data in land cover, soil type maps, slope maps, and climate data. The SWAT simulation was carried out in the 2012 to 2021 timeframe. The sedimentation values obtained from the SWAT model were sediment values from 0.06 to 34.073.01 tons/ha (55.34%), sediment values from 34.073.01 to 95.323.59 tons/ha (23.27%), sediment value 95.323.59 to 225.951.47 (13.51%), sediment values 225.951.47 to 442.013.09 (6.23%), and sediment values from 442.013.09 to 1,415.454.83 (1.66%). Based on this research, it can be concluded that the highest average sediment is found in the downstream area, with an area of 38,875.66 ha.