Flood risk zone mapping using rational model in a highly weathered Nitisols of Abakaliki Local Government Area, South-eastern Nigeria

Abstract

The lack of spatially explicit flood hazard mapping has hampered the development of appropriate flood interventions at community levels in Nigeria. This paper reports on a work conducted to develop a local government level flood hazard map to delineation flood vulnerable areas. Flood vulnerability mapping in this work was addressed from a perspective of administrative unit as the unit of investigation. The study is anchored on the Modeling Flow based on Relational Rule for flood assessment using ArcGIS in combination with modified rational model. The output of the modified rational model was integrated into the Geographic Information Systems environment by the arithmetic overlay operation methods. The results show that the delineated areas/sub-catchments however experienced the same rainfall intensity of 414.2 mm/h but the flood extents in the areas are different. For instance, the very high flood risk zone covers about 22.8% of the study area while the low risk zone covers about 44.3% and the possible areas likely to experience seasonal floods with a given rainfall input are mostly below 40 m elevation. The results of this study will be helpful to prioritize development efforts at grassroot in the study location and to formulate flood adaptation strategies.