A Geospatial Technology Based Study on Flood Risk Assessment: A case of Akaki Kality Sub City, Addis Abeba, Ethiopia

Abstract

Floods are one of the most common natural disaster in the world and causes of lives, livelihood and property destruction. Akaki Kality sub city was suffering from rainy season flood owing to several factors solid waste management generated from household and institution, increase population size (people dwelling near to stream). Accordingly, this leads to increase the occurrence of flood which creates socio- economic crises in the sub city. The objective of this study is to asses flood risk in Akaki Kality Sub-city using the application of geospatial technology. Flood risk assessment was done using flood vulnerability factors such as, drainage density, slope, elevation, rainfall, soil type and land use were rated and combined to delineate flood risk zones using a multi-criteria evaluation technique in a GIS environment. Therefore, the weight of each flood vulnerability factor was computed by pair wise comparison for a final weighted overlay analysis of all factors to delineate the flood risk map. Landsat image for 2009 and 2019 were used to classify the area in to cultivated land, forestland, grassland, settlement and wetland. The mapped data from satellite image of 2009 indicated that cultivated land covered for 5822.4ha, forestland covered for 1341ha, grassland covered for 456.5ha, settlement covered for 2282.8ha and wetland covered for 2442.7 ha from the total area of 12345.4 hectare covered. In 2019 there was cultivated land covered for 4364.4ha forestland, covered for 363.3ha, grassland covered for 290.1ha, settlement covered for 3197.9ha and wetland covered for 4129.7ha from the total area of 12345.4 hectare covered. The cultivated land decreased by 1458ha (25.0%) and forestland decreased by 977.7ha (72.9%). During this period grassland also decreased by 166.4 ha (36.45%). But, settlement and wetland were increased by 915.1ha and 1687ha which represents 40.1% and 69.1% rise respectively. Moreover, these changes alter surface runoff and affect soil infiltration capacities, which increase the occurrence flood in the study area. Finally, this flood risk map indicated that 30.2ha (0.2%), 1068.32ha (8.7%), 9057.24ha (73.4%) and 2189.64ha (17.7%) subjected to low, moderate, high and very high flood risk map respectively. Furthermore, proper land use management and afforestation, is significant to reduce the adverse effects of flooding particularly in the low-lying flood prone areas.