Geospatial Analysis of Flood Drivers and Flood Risk in Ayamelum Local Government Area, Anambra State, Nigeria

Abstract

Flooding remains one of the most recurrent environmental hazards affecting communities, infrastructure, and agricultural activities in many parts of southeastern Nigeria. Ayamelum Local Government Area of Anambra State experiences frequent flood events due to its low-lying terrain, extensive drainage networks, and floodplain characteristics. This study employed geospatial techniques to analyze the drivers of flooding and assess flood risk within the study area. Five flood-influencing factors, namely elevation, slope, flow accumulation, proximity to natural drainage channels, and watershed characteristics, were derived from a 30 m Shuttle Radar Topography Mission (SRTM) Digital Elevation Model. The factors were standardized using fuzzy membership functions to establish a common suitability scale and subsequently weighted using the Entropy Weighting Method to determine their relative contributions to flood occurrence. The weighted factors were integrated using a Weighted Linear Combination approach to generate a Flood Risk Index and delineate flood risk zones. The results showed that flow accumulation (0.313), proximity to drainage channels (0.267), and elevation (0.231) were the most influential flood drivers, while slope (0.145) and watershed characteristics (0.044) exerted relatively lower influence. Flood risk assessment revealed that 422.92 km² (72.26%) of the study area falls within the Very Low Risk category, 74.91 km² (12.80%) within the Low Risk category, 70.08 km² (11.97%) within the Moderate Risk category, and 17.40 km² (2.97%) within the High Risk category. High-risk zones were concentrated mainly within Umuerum and Anaku wards, while moderate-risk conditions extended across Omor 1, Omor 2, Omor 3, Umuerum, Igbakwu, and Anaku wards. The study demonstrates that flood susceptibility in Ayamelum Local Government Area is controlled largely by the interaction of topographic and hydrological factors. The resulting flood risk map provides a valuable decision-support tool for flood management, land-use planning, disaster preparedness, and sustainable environmental management within the study area.