International Journal of Research and Scientific Innovation (IJRSI) | Volume VIII, Issue I, January 2021 | ISSN 2321–2705

 Flood Risk Mapping and its Effects on livelihood in Ghana using Sentinel-1 data. A case study of Accra

E. Njomaba¹, J. N Ofori², B.E. Aikins³, D. A. A Nyame^4
1Laboratory of Geo-information Science and Remote Sensing, Wageningen University & Research, Gelderland, Netherlands
²Dept. of Plant Ecology and Nature Conservation, Wageningen University and Research, Droevendaalsesteeg 3, Wageningen, Gelderland, Netherlands
³Remote Sensing & GIS Unit, Bedeston Technologies, and Consulting Services, Accra, Tema, Ghana
⁴Department of Geography & Resource Development, University of Ghana, Legon

Abstract: Flooding has been a major issue in Ghana, and several driving factors have been attributed to flooding in Accra. Among the factors outlined throughout the literature are climatic influences such as rainfall which results in a change in the natural hydrology of the area. Other causes include building in waterways and dumping of refuse in the drainage area. This paper seeks to develop an operational methodology using Synthetic Aperture Radar images to support the response agencies by providing timely information on flood risk areas over a period to prioritize response activities within the Greater Accra Metropolitan Area (GAMA) area. The method used was a change detection algorithm where the after-flood mosaic was divided by the before-flood mosaic, resulting in a raster layer showing the degree of change per pixel. Additional Dataset to refine the flood layers were adopted such as Digital Elevation Model (DEM) and Global Surface-water dataset. One of the major findings of this study is that the Ga south district is the district with the highest average flooding extent compared to the other districts within GAMA and the main reason was because of the Weija Dam being situated close to the district. When the Dam is full and being spilled over, it causes surrounding environments to experience flooding. The implication is that much attention should be given to the Ga south district to curb the menace of flooding in GAMA.

Keywords: Digital Elevation Model, Ground Range Detection, Interferometric Wide Swat, Multicriteria Decision Approach, Synthetic Aperture Radar.

I. INTRODUCTION

Over the past decades, flooding has become a global issue, which affects economic and social development. This global issue has in most cases led to the loss of lives and damages in most countries including Ghana. Aside from demographic growth, urbanization trends, and climate change, the causes of floods are shifting, and their impacts are being felt. Most flooding happens in urban areas when there is prolonged rainfall and water drainage facilities can no longer contain the surface running water. Flooding is triggered by a lot of factors. Floods which have serious environmental and social implications have been mostly caused by a climate-related factor such as severe rainfall and in some cases severe snowmelt as well (CRED, 2015).

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