Integrated a GIS and Multicriteria Evaluation approach for Mapping Flood Vulnerability of Buildings in the Grande Niaye Watershed of Dakar, Senegal

The watershed of Grande Niaye in Dakar is precisely located in the center-west of the Dakar region, capital city of Senegal. This basin, because of its wet ecosystems mainly called “ Niayes ”, seems fairly representative of areas at significant risks to flooding in the Dakar region and especially in its peri-urban area. Based on the diversity of factors that are considered responsible for flooding, this study aims to draw attention by evaluating the vulnerability of the watershed to flooding using GIS and Multicriteria Evaluation Approach (MCE). This study considered six factors as indexes of flood vulnerability identification and these included elevation, slope, groundwater level, soil type and the distance between dwelling areas and wetlands. These information were derived from aerial photograph of 1942 and satellite image of 2014, SRTM, nature of soil and groundwater level data of the study area. The data is standardized to facilitate the processing treatment. The criteria are then reclassified, scored, and weighted before being conducted to an aggregation step using the weighted linear combination (WLC) method to rank the various vulnerabilities of builds, using weighted sum overlay tool in ArcGIS 10.2 platforms. The modeling study and analysis of the results indicate four levels of vulnerability: highly vulnerable, moderately vulnerable, vulnerable and lowly vulnerable. As a result, 75% of the Grande Niaye watershed area is approximately vulnerable to flooding. Moreover, about 50% of the houses and buildings services occupy the vulnerable surfaces of the watershed. Overall, the results indicate that the study area constitutes a great danger to the well-being of the populations. In order to sustainably reduce flooding in the area, policy makers, urban planners and managers must, in the long term, promote a management policy based on the preservation and rehabilitation of wetlands in the Niaye. Indeed, their main function is the capture, regulation and the management of the full of waters due to the high vulnerability to the flooding of the buildings that are built in these wetlands.