THE APPLICATION OF THE SWAT+ MODEL FOR WATERSHED MANAGEMENT SCENARIOS IN LAHAR FLOW AREAS OF MERAPI VOLCANO

This research aimed to analyze the surface runoff using the SWAT+ model and developed scenarios for watershed management that followed the environmental and community conditions. To achieve this objective, the analysis requires parameters such as land use, soil types, morphology, climatology, and hydrology, which were collected from primary data sources and supplemented by secondary data from relevant stakeholders. The SWAT+ method was employed to delineate watershed boundaries, construct a Hydrologic Response Unit (HRU), edit and input parameters, and perform calibration and validation. The watershed management scenario was developed by altering land use to define conservation areas and buffer zones. The results were then calibrated and validated using multiple tests. Calibration results yielded NSE= 0.52, PBIAS=7.38, and R2= 0.79, while validation showed NSE= 0.50, PBIAS=-5.45, and R2= 0.58. The values of this statistical test were greatly influenced by the quality and length of the data. The analysis also explored how changes in land use affect runoff values, considering factors like Curve Number (CN) values, recharge area classes, and land use patterns (e.g., clustered or dispersed). This analysis takes into account various hydrological parameters, including evapotranspiration and surface runoff, which are influenced by the land's ability to retain water. Additionally, values like lateral flow, return flow, and recharge are affected by the location of land conversion within the watershed (e.g., upstream, midstream, or downstream). The findings from this analysis allow for adjustments in watershed management efforts to align with the desired changes.