GIS AND RS BASED FLOOD HAZARD SUSCEPTIBILITY MAPPING USING AHP METHOD FOR THE LOWER AWASH RIVER BASIN (LOGIA-DUBTI AREA) AFAR, ETHIOPIA

In recent time, floods are considered amongst the most catastrophic, frequent and widespread natural disasters worldwide causing severe economic and environmental damages as well as destruction of livelihoods. Flood mapping is an effective way to assess flood susceptible areas and determine factors that cause floods. This study aimed to define flood causative factors and develop flood hazard susceptibility map of the Lower Awash River Basin (Logia to Dubti), Afar region, Ethiopia using Geographic Information System (GIS) with the Analytical Hierarchy Process (AHP). The methods used in this study was the combination of: (a) field assessments of flood affected areas (using features of water-level markers), and (b) Geographic Information Systems (GIS) and Weight Linear Combination Technique (WLC). A total of six influencing factors were used for the AHP method, namely slope angle, soil types, land use/land cover, geology, elevation, and drainage density. All the parameters were overlaid in geospatial software. The AHP method is utilized in this study to find relative weight and produced pair wise comparison weighted criteria of the influencing factors. The findings of this study shows that slope is the most significant factor contributing to flooding because it was the highest weight criteria at 37 % while the least significant factor is drainage density at 4%. The consistency ratio (CR) value was 0.07 which is acceptable as this value is lesser than 0.1. Flood hazard susceptibility map of the study area was produced by applying pair wise comparison based on weighted criteria in Arc GIS environment by using the weighted overlay method. The final map was consists of 10 𝑘𝑚2 (4.15%) very high flood susceptibility, 94 𝑘𝑚2 (39%) high susceptibility, 114 𝑘𝑚2 (47.5%) moderate susceptibility and 23 𝑘𝑚2 (9.54%) low susceptibility. However, moderate areas can change into high susceptibility and very high susceptibility if no proper flood management is taken.The flood susceptibility map was further validated by using the ground truths data (GPS point) obtained from locations that had experienced flooding and the data were analyzed by using GIS software. These validation results demonstrated a strong agreement between the predicted flood prone area and actual flooded location, conforming the accuracy and reliability of developed flood hazard susceptibility map. The study findings are crucial for improving flood response measures as well as for implementing mitigation measure such as, forecast and warning system, and maintaining and updating structural flood protection measures. Therefore, the findings of this study can be used for further research and environmental management of flood hazards in the study site. .