Flood Hazard and Risk Assessment of Lower Magat River Basin Using Geospatial Technologies: Basis for Developing Flood Hazard Map

Abstract

This study provides a comprehensive geospatial assessment of flood susceptibility in the Lower Magat River Basin, focusing on the municipalities of Solano, Bayombong, Quezon, and Bagabag in Nueva Vizcaya. The study addresses the escalating threat of inundation by utilizing the Analytic Hierarchy Process (AHP) to evaluate and weight six critical parameters: distance to rivers, precipitation, elevation, slope, soil type, and land use/land cover (LULC). Results indicate that Distance to Rivers (36.1%) and Precipitation (25.4%) are the primary drivers of flood hazard in the region. The integration of these factors through weighted overlay analysis reveals a heterogeneous distribution of risk, with Solano exhibiting the most pervasive vulnerability, as 71.72% (48.04 sq.km) of its land area is classified as high susceptibility. In contrast, Bayombong and Quezon harbor the most extreme localized risks, with Barangays Casat, Darubba, and Runruno emerging as critical "Very High" hazard hotspots. The findings demonstrate that high-risk zones are concentrated within a 600-meter buffer of the Magat River, particularly where low-gradient slopes (0–5.8%) and heavy clay soils impede drainage. The study achieved a high consistency ratio (CR < 0.10), validating the model's reliability for land-use planning. It is recommended that local government units integrate these susceptibility maps into their Comprehensive Land Use Plans (CLUP), enforce strict river easement zones, and implement nature-based solutions like reforestation to mitigate runoff. This research serves as a critical baseline for disaster risk reduction, providing a data-driven framework for enhancing community resilience against future flooding events.