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FLOOD VULNERABILITY MAPPING OF KOSOFE LOCAL GOVERNMENT AREA, LAGOS, NIGERIA
*Atagbaza A. O., Olayinka D. N and Pepple G. T.
The devastating nature of the floods on the environment that causes loss of lives and properties thus necessitates the need for flood vulnerability maps. This research identified and delineated area liable to flood and subsequently generate vulnerability maps that will aid in the efficient management of flood and flood related issues. This study identified heavy rainfall as the major cause of flooding which results in the overflow of the Ogun River. Land cover Analysis was carried out and six major land cover types were identified namely: Bare earth, Built up Area, Water-body Mangrove, Vegetation and Wetland. Results obtained from the analysis performed showed that bare earth decreased by 0.75km2 (1984 - 2002) and further decreased by 0.4km2 (2002 - 2013), built up area also showed a marked increase of 25.83km2 (1984 - 2002) to 1.35km2 (2002 - 2013). Mangrove had significantly decreased was as a result of rejuvenation 6.05km2 to 0.64km2 while vegetation and wetland decreased marginally from 15.87km2 to 9.18km2 and from 11.58km2 to 6.47km2 both between 1984 and 2013 respectively. The area occupied by water-body increased slightly within the period of this study which implies that the wetlands were lost due to human encroachment and urbanization i.e. reclaimed and used or transformed into built-up area which explains the increases in the settlements in Kosofe LGA. Some of the environmental consequences of this land cover change and alteration of coastal habitats are known to include erosion, flooding, pollution, threats to groundwater, effects of climate change and rising sea levels (UNEP, 2002; Okude and Ademiluyi, 2006; Brody et. al, 2007). Two methods are used in this research to identify flood, generate vulnerability maps and identify infrastructures at risk. The first method is „bath-tub? method, a zero dimensional approach method using the Arc-GIS 9.3 environment to produce maximum flood extent for different flood scenarios. The second one is CAESAR model, a two dimensional flow and sediment transport model than can simulate morphological changes in river catchments or reaches, on a flood by flood basis, over periods up to several thousands of years. The model results show flood extent spread at different flow regimes with infrastructures at risk in the area and the method results show flood vulnerability maps at normal, medium and worst flood scenarios.[Full Text Article]