Land use planning for mitigation of erosion, sediments, and stabilization of water discharge in the Mamasa Watershed

Watershed Ecosystem is an important part. Activities in a watershed that cause changes in the ecosystem, such as land cover change, especially in the upstream area, can have an impact on downstream areas in the form of change in water flow fluctuation, sediment content and other dissolved materials. The Bakaru reservoir is located in the downstream of Mamasa watershed. In its development, the Bakaru Hydroelectric Power Plant could no longer produce electricity as planned, because of the rapid sediment rate. This research was conducted to determine the amount of erosion, sediment, and water discharge, formulate land use spatial patterns in the watershed. Data analysis was performed by using the SWAT (Soil and Water Assessment Tools) model. Input data needed in the analysis are spatial data, thematic maps such as land use map, soil type map, and Digital Elevation Model data. The results of this study indicate the total erosion of the analysis period is 1,014,576.51 tons/ha/year. The amount of erosion, which is quite high, affects the total sediment (132,852,500.03 tons/year), and the total water discharge generated is around 420,715.54 m³/s. While the output generated using spatial pattern data shows much better results. The total erosion produced was 50,863.86 tons/ha/year, while the total sediment amounted to 14,903,914.25 tons/year and water discharge 48,697.00 m³/s. Based on these results, it can be said that if land use is adjusted to a predetermined spatial pattern, then the results of erosion and sediment can be tolerated, and water discharge can be maximized. The direction of optimizing land cover, mainly forest land cover, is in accordance with the proposed spatial patterns that have been set in each district. The implementation of the direction of optimizing forest land cover adjusted to the spatial pattern is expected to be a strategic alternative in maintaining the erosion balance in the upstream, sediment, and water discharge at each river outlet.