Integrating GIS-AHP and HEC-RAS for Flood Risk Indexing and Floodplain Mapping in Bagac, Bataan, PhilippinesPages 171-178
Abstract:
Floods pose a growing threat to low-lying coastal communities in the Philippines, yet local risk assessments remain limited. This study presents a comprehensive framework combining Geographic Information Systems (GIS), the Analytical Hierarchy Process (AHP), and the Hydrologic Engineering Center’s River Analysis System (HEC-RAS) to produce both a spatially explicit Flood Risk Index (FRI) and detailed floodplain extents for Bagac, Bataan. The FRI synthesizes four core dimensions—hazard, exposure, vulnerability, and coping capacity—through seven indicators, including seasonal precipitation, digital elevation, land cover, population density, household count, medical personnel distribution, and existing mitigation infrastructure. Pairwise comparisons in AHP yielded weightings that were applied in QGIS to classify the municipality into five risk tiers, from Very Low to Very High. In parallel, a 1-D unsteady flow simulation in HEC-RAS, validated against historical flood records, delineated inundation depths and extents for the 25-, 50-, 100-year return periods. The resulting maps reveal critical hotspots along the coastal plain and riparian corridors, pinpointing communities and infrastructure most susceptible to flooding. These outputs offer decision-makers a robust toolset for land-use planning, early-warning system design, zoning regulation, and targeted mitigation investments. By integrating multi-criteria risk scoring with hydraulic modeling, this workflow advances localized flood resilience planning and can be readily adapted to other Philippine municipalities facing similar climate-driven challenges.
Keywords: Flood Risk Indexing, Geographic Information System (GIS), Analytical Hierarchy Process (AHP), HEC-RAS, Floodplain
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