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 it’s peak in the rainy seasons (April-October) of every year resulting to loss of life and economic valuables/properties. In order to curb this menace, an integrated solution (combination of empirical hydrological models with remote sensing and GIS capacity) is thus herein presented using a downloaded Digital Elevation Model of the study area to delineate water shed, flow direction, contributing areas and flow path/Channel. Also, surface runoff was simulated for an eight hours homogenous rainfall and the resulting gauge readings from eleven (11) fictitious gauge station distributed across the state was obtained. The study was able to produce a map categorising Lagos state into three (3) zones on the basis of their vulnerability to flood. The Quantum GIS software was used for the analysis and simulation.