SPATIAL ASSESSMENTOF FLOOD RISK FACTORS AND VULNERABILITY MAPPING IN SULEJA DISTRICT OF NORTHERN NIGERIA

This study aim at assessing flood risk factors and mapping areas vulnerable to flood in the study area, using Geo-spatial techniques. The method follows a multi-parametric approach and integrates some of the flood causative factors such as: rainfall distribution, elevation and slope, drainage network and density, land-use/land-cover and soil type. The Spatial Multi-Criteria Analysis (MCA) was used to rank and display potential locations, while the Analytical Hierarchy Process (AHP) method was employed using pair-wise comparison to compute the priority weights of each factor. The various layers were integrated in weighted overlay tool in ArcGIS to generate the final vulnerability map, representing three levels of estimated flood vulnerability zones (high, moderate and low). The normalized criterion weights were obtained for each factor, and the results shows that, rainfall (34) and slope (31) have the highest influence on flood in the study area.The Consistency Ratio (CR) with an acceptable level of 0.05 was obtained which further validated the strength of the judgement. With ArcGIS, the factor weights from the AHP were incorporated to produce a Geo-hazard map and it showed that areas that are high vulnerable to flood in Suleja constitute about 37%, while moderate and low vulnerable areas constitute about 45% and 18% respectively. Elements at high risk of flood are those found at the extreme northeast, where elevation is very low, southwest where rainfall distribution is high (along the fringes of Tafa LGA and Abuja FCT respectively) and on low lying areas along the depressions. Therefore using the Geo-hazard map as a guide, local councils and other stakeholders can act to prepare for potential floods when the rains come or, better yet, proactively promote an appropriate land-use policy that will minimize threat to lives due to flood.