Modelling Surface Runoff and Mapping Flood Vulnerability of Lagos State from Digital Elevation Model

Abstract

Flooding in recent times has become a critically problematic phenomenon of spatio-temporal order and considerably high frequency of occurrence all over the world, and most especially in coastal nations/states. Lagos State, one of the nine (9) Coastal States of Nigeria, has witnessed and is still witnessing multivariate cases of flooding which attains its peak in the rainy seasons (April-October) of every year resulting in loss of life and economic valuables/properties. To curb this menace, an integrated solution (combination of empirical hydrological models with remote sensing and GIS capacity) is thus presented herein using a downloaded Digital Elevation Model of the study area to delineate watersheds, flow direction, contributing areas, and flow path/Channel. Also, surface runoff was simulated for an eight-hour homogeneous rainfall, and the resulting gauge readings from eleven (11) fictitious gauge stations distributed across the state were obtained. The study was able to produce a map categorising Lagos state into three (3) zones based on their vulnerability to flood. The Quantum GIS software was used for the analysis and simulation.