SOCIO-ECONOMIC IMPACT OF COASTAL FLOODING AND SHORELINE CHANGES ON VICTORIA ISLAND,LAGOS STATE, NIGERIA.

Abstract

This study examines the impact of coastal flooding and shoreline changes in Victoria Island, Etiosa Local government area of Lagos State. The research was conducted using questionnaire and Geographic Information System (GIS) to collect the required data for the purpose of fulfilling the objectives of the study. Structured questionnaires were administered specifically in Victoria Island where flood hazard was prominent. There were 3248 buildings in the study area which constitute the research population. The sample size of 10% was adopted, hence 325 copies of questionnaires was administered in the study. Multiple regression was used to test the relationship between flooding and the socio-economic activities, the relationship between flooding and refuse disposal was also tested using correlation. The study adopts GIS to examine flood hazard and shoreline changes in the study area and its environs. The digital elevation model (DEM) and slope map was generated from the topographical map of the study area. Topographical map of 1962 was used as the base map; Landsat TM of 1984, ETM+ 2000 and 2011 of Eti-osa was used for this study while all geo-processing operations and analyses were carried out in ILWIS 3.1 and ArcGIS 9.3. The topographic map was digitized to vector, polygonised and then converted to raster map of 10m pixel size. Supervised image classification was done for each year to classify the imageries into about six land use categories. The classified imagery for each year was vectorised and polygonised, then was converted to raster to have 10m pixel resolution size for all the imageries to make crossing possible for the analysis of the shoreline changes. The rasterized topographic map of 1962 and the imagery of 1984 was glued and crossed; 1984 and 2000; and the 2000 and 2011 were also crossed to get the changes in the shorelines in these years. Findings show that, narrow drainages coupled with high rainfall in the study area are the major causes of flooding. DEM map shows that the study area is between 0-33.33m, while the slope map shows the Elevation range, revealed that about 90% of the study area is between the heights of about 0-16.667. The results of the analysis reveal that between 1962 and 1984 there was loss in landmass while between 1984 and 2011 there was increase in land gain overtime. About 31.4% of landmass was lost between 1962 and 1984 while between 1984 -2000 and 2000-2011 there was gain in landmass of about 81.89% and 62.11% respectively. To reduce the effect of flooding and shoreline changes in the study area, policy measures were recommended based on the research findings. These include construction of standard paved surface and drainages, law enforcement on waste disposal, integrated approach to flooding management and control, flood insurance policies, provision of flood hazard zone maps, and construction of hard and soft structural engineering options