ASSESSING THE SUITABILITY OF NATURE-BASED SOLUTIONS (NBS) FOR FLOOD RISK REDUCTION: A CASE STUDY OF THE SERAYU WATERSHED IN PURBALINGGA REGENCY, CENTRAL JAVA

The Serayu Watershed is one of the critical watersheds in Central Java, particularly in the upstream. Aim: This study aims to assess the suitability of nature-based solutions (NBS) in flood risk reduction in the Serayu Watershed. Methodology and results: The collected data included the Serayu Watershed boundary and spatial datasets, consisting of a Digital Elevation Model (DEM), infiltration area map, soil erosion map, land use map, and slope map. The authors applied a spatial analysis method using the Geographic Information System (GIS) to integrate historical flood data, population density, topography, slope, geology, soil type, land use, water catchment area, water absorption area, groundwater basin, and erosion rate. The study found that within 10 years (2014-2023), 54 villages were exposed to flooding with a total area of ​​6,453.3043 ha or 8.010% of the area of ​​Purbalingga Regency. The analysis of land use changes from 2017 to 2022 shows a significant decrease in the area of ​​plantation forests-by 225,477.67 ha, from 323,979.26 ha to 98,501.58 ha. Conclusion, significance, and impact study: This study examines the regional characteristics and flood patterns of the Upper Serayu River in Central Java, Indonesia. Drawing on spatial analysis and hydrological data, the findings identified five NBS recommended for implementation: river floodplain restoration river and stream renaturation, building-related interventions, bioretention areas, and urban farming. These strategies align with local geormorphological conditions and offer sustainable approaches to flood mitigation. This study contributes to regional policy-making and supports the development of flood risk management in the Upper Serayu Watershed.