This study applied Geographical Information System Technology in the spatial analysis of flood risks in Aba metropolis. Data on spot heights and elevation were collected with Global Positioning System and used to produce digital elevation model map in a 2-D format; the aspect map showed the natural direction of storm water flow; the slope map was used to indicate the overall rate of downward movement of water and the contour map showed elevations at intervals of 10m. The digital elevation model presents the study area as ranging from 35 – 70m above sea level. Water flowed from areas 70m to areas 35m above sea level. Areas 35-39m and 43-48m are prone to flooding, as runoff from the areas of higher elevations tends to flow towards areas of lower elevations. The percentage slope variation showed that slopes which ranged from 38.26% - 46.88% and areas 55.50% - 64.12% are more vulnerable to erosion but flood free. The areas with slopes ranging from 64.12% - 72.74% and areas 81.36% - 89.98% have critical and steeper slopes and certainly produce flood of greater velocity than moderate or lower slopes. The aspect map showed that in areas of 0 - 22.5 and 337.5 - 360 water flows to the north, while 67.5 - 112.5 flows to the east. All areas of 157.5 - 202.5 water flows in the southern direction, while areas from 247.5 - 292.5 water flows in the western direction. Elevation in the area ranged from 72m to 36m with an average of 54m and must be considered in storm water channelization projects.

Keywords: urban flood, geographical information system, spatial analysis, elevation

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