Background: Flood is one of the most destructive natural disasters of climate change effects in West Africa. Flood risk occurrence is a combination of natural and anthropogenic factors, which calls for a better understanding of its spatial extent. The aim of this paper is to identify, and map areas of flood risk in Abidjan district. Results: This work is based on the integration of multi-criteria data including slope, drainage density, type of soil, Isohyet, population density, land use and sewer system density within ArcGIS interface. The resulting AHP flood risk map shows that areas under high and very high flood risk covers 34 % of the study area. Conclusion: The Analytic Hierarchy Process (AHP) method used as a multi-criteria analysis allowed the integration of several elements under two criteria, hazards and vulnerability, for flood risk assessment and mapping. Results revealed that, Abidjan district is heavily exposed to the risk of flooding. Eight out of thirteen (8/13) municipalities within the district are at a high risk of flooding which calls for decision makers to effectively develop strategies for future flood occurrences within the Abidjan district (South of Côte d'Ivoire).

The importance of small reservoirs during droughts for the local population in most semi-arid environments cannot be over estimated. Water stored in these reservoirs allow for all-year-round irrigated agriculture for some farmers and ensures that there is little or no domestic and drinking water shortages for the local population during dry periods. In order to manage the water effectively for competing uses, the actual storage of these reservoirs need to be accurately estimated. Recent attempts to delineate these reservoirs using remote sensing with Landsat imagery have been quite successful especially in the Upper East region of Ghana, West Africa. This was done to determine the number; spatial distribution and storage volumes of reservoirs for effective water management and reservoir planning. However, the accuracy of the lateral delineation of these reservoirs needs further studies since it is paramount for its monitoring especially for purposes such as forecasting of crop failure in the dry seasons.This thesis explains how radar images (ENVISAT-ASAR) can be used to provide all year-round monitoring. Radar has the important advantage that it is independent of cloud cover hence can be used in the rainy season. It can also be used to acquire both day and night time images. This study shows how a monthly regional inventory of storage in small reservoirs can be obtained. The study area is the Upper East Region of Ghana, West Africa. In comparing ground data with ENVISAT data, it becomes clear that reeds, which often can be found in the shallow tail-ends of reservoirs, can not be readily distinguished from the surrounding vegetation.

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Many small dams and dugouts have been constructed in the Upper East Region of Ghana to address the problem of regional water scarcity. The reservoirs were constructed primarily as water supplies for agricultural irrigation and livestock watering, aquaculture and domestic use. However, many of the reservoirs dry up during the dry season, affecting the livelihoods of their basin inhabitants. A major cause for the dried reservoirs is siltation, which reduces the reservoir's storage capacities. The goal of this study is to quantify the annual siltation rate of four study reservoirs, using a bathymetric survey and reservoir soil sampling. The sediment yield and its relation to catchment area also were assessed. The results of this study indicate that the annual siltation rates are 1272, 3518, 2764 and 6135 t year )1 for Doba, Dua, Zebilla and Kumpalgogo reservoirs, respectively. Analyses of the sediment yield and catchment areas illustrated that the sediment yields decreased with increasing catchment area. All the study reservoirs have lost their dead storage capacity, which was meant to store sediment until the end of their anticipated design lives. The decreasing storage capacity because of siltation will affect the livelihoods of the local basin inhabitants, as the reservoirs will not be able to achieve all their intended purposes. The results of this study indicate that, because siltation is not the only factor threatening the benefits gained from the reservoirs, the integrated assessment of all relevant factors is required.