Mapping Seasonal Flood Inundation and Developing an Early Warning System for Lagos Metropolis (Nigeria): A study between 1990 and 2011

Document Type : Original Article


Department of Geography, Faculty of Social Science, University of Lagos, Lagos, Nigeria



Flooding has become a major environmental hazard in Lagos metropolis in recent years due to its topography, population growth, rapid urbanization and extreme weather events such as rainfall. Seasonal flood inundation simulation was modeled and an early warning system was developed for Lagos metropolis using DEM (Digital Elevation Model) from SRTM (Shuttle Radar Topography Mission) and monthly flood stage between 1990 and 2011 using GIS (Geographic Information System) technique. Annual rainfall trend was studied between 1971and 2013 using time series statistic as well as seasonal rainfall distribution between 1971 to 1999 and 1999 to 2013. Seasonal flood stages were studied and used as input in flood simulation. Flood inundation simulation was modeled using HEC-RAS program for 1-in-20 year return period. While the flood hazard map was prepared based on flood inundation level. Risk assessment was performed to produce a flood risk map for Lagos metropolis. Flood velocity, runoff time, depth, duration, location and spatial dimension were captured, studied and used to develop a Flood Early Warning System (FEWS) as well as flood discharge for Lagos metropolis. Affected Local Government Areas and streets were selected to study the impact of flooding on Lagos residents. Finally, research findings and recommendations were highlighted for Lagos metropolis.


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