3D modeling for flood inundation height mapping based on QGIS and WebGIS in Surakarta

Abstract Pucangsawit village is one of the areas in Surakarta City that experiences annual flooding from Bengawan Solo river’s overflow. Creating 3D flood inundation models and data dissemination in WebGIS can help reduce the risk of loss experienced by local communities. This study aims to model the areas and buildings affected by flood inundation. A spatial data processing using national digital elevation models (DEMNAS) data in the QGIS was conducted, producing inundation height for scenarios <= 50 cm, 100 cm, and 150 cm. Inundated areas were then overlaid with building shapefiles to determine the number of buildings affected by each height scenario. We delineated each building into sections, including public facilities, residential areas, and shops. For model validation, we directly observed the affected areas and interviewed regional officials and local community members. Our results show that 75% of the 3D modelling can be effectively applied for flood inundation mapping, obtaining an accuracy of 75% for both user’s and producer’s accuracies in affected regions by overflow category. Based on the outcomes, the inundation area extends northward, affecting densely populated settlements (± 86 hectares). We also observed that the residential areas located closest to the riverbank and the relatively sloping contours face the most significant potential impact during floods. These results suggest that the modelling is suitable for flood inundation scenarios, allowing for direct visualization of specific heights during flooding events.