Abstract
Maiduguri metropolis Nigeria, lies on a relatively flat terrain of about 350 meters above sea level and is part of the undulating Borno Plain that slopes towards the Lake Chad. The rapid physical expansion of the metropolis and the annual recurrent flash flooding and inundation problems within the city continues to impact devastating socioeconomic effects on the livelihood of residents sometimes leading to loss of lives and property. It is important therefore to understand the spatial pattern of floods and terrain characteristics in Maiduguri for planning purposes. The paper examined the spatial pattern of urban flash floods and inundations, and the terrain characteristics in Maiduguri metropolis. Digital Terrain Model (DTM) generated from the Shuttle Raddar Topography Mission was used to provide the basis for the terrain analysis to generate hydrological parameters such as elevation, flow accumulation and direction, drainage network and slope angle as well as classified elevation images and terrain wetness index to map out potential flood risk areas. The DTM identified potential areas liable to flash flood and inundation. The 3D Digital Terrain Model (DTM) of the area showed where potential floods or traps were located in the metropolis. The findings further revealed that Maiduguri was generally characterized by low lying locations with slope angles of less than 5 degrees covering an area of 144.4 km2 out of 148 km2 making it extremely difficult to drain. The processed flow accumulation of the study area showed a high flow accumulation pixel value of 19,972 that drained into outlet, suggesting that a large proportion of the study area was getting flooded during a rainstorm. Even though the calculated drainage density of 0.73 for the study area indicated a very good drainage system, this was also undermined by the flat terrain and urbanization. The study recommends for improved land use planning; raising awareness of the residents, provision of more drainages and continued vulnerability mapping improved the functionality of bodies responsible for flood management among others for sustainable flood management in the study area.
Highlights
Flash floods are rapid rise of water along a stream or low lying sections of the urban area usually caused by heavy rainfall
These images were extracted from SRTM Digital Elevation Model (SRTM DEM), 90m spatial resolution and clearly displayed the potential inundation areas with poor drainage conditions
The area is very flat in nature as indicated by the 3D Digital Terrain Model (DTM) and is characterized by a very good and well fashioned natural drainage system but is taken over by poorly planned urban development rendering them less effective
Summary
Flash floods are rapid rise of water along a stream or low lying sections of the urban area usually caused by heavy rainfall. Flood risk maps are very essential tools in the identification of flood vulnerable areas [3]. Production of flood risk maps in developed countries has become an important criterion for carrying out some major development interventions [4]. Some flood risk assessments have been done in some major cities in the country but the flooding menace is on the rise, as more than half of the states in the country have been hit by floods [1]. It is necessary that flood risk maps are produced for all major urban cities of the country as crucial tool for monitoring flood risk
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