Flood Hazard And Risk Assessment Of Upper Awash Basin Using Geographic Information System: A Case Of Barga River, Oromiya, Ethiopia.

Abstract

Flood is one of the natural hazards in worldwide both in terms of the frequency of occurrence and resulting damages. Ethiopia is a country which affected by flood in many parts of the country. The aim of this study is to identify the flood hazard and risk assessment of the Barga River using Geographical Information System (GIS) using multi criteria evaluation method. The factors that cause like: slope, elevation, soil type, geology, rainfall, drainage density, flow accumulation, topographic wetness index and land use land cover, these parameters was reclassified based on the susceptibility for the flood. Slope, elevation, drainage density, flow accumulation and topographic wetness index was derived from Digital Elevation Model (DEM) which have (12.5 x 12.5 m) spatial resolution. The other factors like: land use land cover was get from Ethiopia map service agency in raster, soil type, geology were collected from ministry of water, irrigation and electricity in the shape file form change to raster form using Arc GIS10.4.1and (1991 to 2018) daily rainfall was from meteorological service agency. The factors ranked and divided into five classes ranging from very low to very high with the integration of Geographical Information System (GIS). Weight of each deriving factors was done by analytical hierarchy process method of the nine by nine matrix was solved in IDRISI 32 software within the Consistency ratio was 0.03 the critical consistency is acceptable. Flood hazard map was done by combination of all factors within weighted overlay method and 19.06%, 20.31%, 28.18%, 22.35%, 10.09459% of the area is under very high, high, moderate, low and very low respectively of flood hazard. Risk map was from the corporation of three parameters like population density, land use land cover and flood hazard map within equally weighted and 0.14%, 8.38%, 64.86%, 26.29%, 0.32% of the total area was under very high, high, moderate, low and very low of flood risk respectively. The flood hazard and risk map produced by GIS was validated using ground truth point location of the flooding area collected during the field surveying. The magnitude of discharge that causes flooding in watershed was calculated from daily peak discharge. The frequency was analyzed by person type III and general logistic method of the best fit selected L-moment method for 2, 5, 10, 15, 20, 25, 50, 100, and 200 of the return period