Application of GIS for flood hazard mapping using basin morphometry : case study : Acowa Sub county.

Abstract

Flood is an inevitable natural phenomenon occurring from time to time in all rivers and natural drainage systems which not only damages the lives, natural resources and environment, but also causes the loss of economy and health. The impact of floods has been increased due to a number of factors with rising sea levels and increased development on flood plain. Recurring flood losses have handicapped the economic development of both. developed and developing countries. The presented work is aimed at using GIS· techniques to produce a potential flood hazard. Map for Acowa Sub County based on geomorphic parameters and to estimate the risk degree of individual sub basin by combining normalized values of the parameters. The study area is characterized by a bimodal type of rainfall, with peak periods in the months of March- June and September-November, however, it experiences pronounced erratic weather conditions quite frequently, manifesting as excessive rainfall within a short period leading to floods and water logging, and then followed by scarce rainfall over a long period of time (not less than 3 month), resulting in drought. Thunderstorms accompanied by heavy winds usually occur at the onset of every rainy season often resulting in destruction of buildings, trees, vegetation, crops and sometimes life occasional hailstorms during rainfall peaks can result into destruction of crops and even livestock. Based on the Aster Digital Elevation Model, the drainage pattern of the Acowa’s sub-basins were delineated. The sub-basins were extracted and. morphometrically analysed to assess flash flood susceptibility. The morphometric parameters were measured by stream number and stream length. The parameters were computed using ESRl's ArcGIS 10.1. The case study results show that 50% of the sub-basins have high susceptibility of flooding and 34% have medium susceptibility and 16% have low susceptibility to flooding Basins or high and moderate flood risk require detailed studies to implement actions to protect these areas against flood. hazard.