R.E. Daffi and J.A. Otun (Nigeria)
Floodplain, Risk, Remote Sensing & GIS, DigitalElevation Model, Watershed, Topography
Floodplains are very fertile lands that attract agricultural and consequently other developmental activities. It is important to identify the areas subjected to floodwater inundation within a watershed in order to manage floodplains for different purposes to prevent unpleasant situations during flood. Floodplains should be viewed at basinal level because for every watershed there are areas that are likely to be floodplains, mostly at the low-lying downstream portions of the watershed. The objective of this study is to identify areas within the Dep River Basin that are susceptible to inundation using only the topographic characteristics of the watershed and utilising remote sensing and geographic information system techniques. The elevation and slope maps were processed using the Digital Elevation Model (DEM) as input map. Floodplain identification was carried out by weighing each of the parameters in the two maps according to probability of flood inundation in the raster cells using map calculation and map crossing in ILWIS 3.3 Academic. Total area of the catchment with Very High Risk of inundation from this analysis is 1416.39km2 (13.35%) while area with High Risk of inundation covers 1674.08km2 (15.77%) with medium risk covering 1854.27 km2 (17.47%) and the area with no risk of inundation is 5667.68km2 (53.41%). The identified floodplains are areas where detailed flood risk analysis can be focused. It is generally recommended that no farming or developmental activities should take place within the area identified as having Very High Risk of inundation except dry season irrigation farming where suitable. Both rainy season and irrigation farming of suitable crops can take place on the High Risk area but other development on the land is strongly discouraged. Any activity can take place at the Medium Risk and No Risk areas but generally river banks should be avoided.
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