Browsing by Author "GIZACHEW MUSIE ALENBO"

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    FLOOD INUNDATION MODELING AND RISK MAPPING OF BIG AKAKI RIVER, ADDIS ABABA, ETHIOPIA
    (Hawassa University, 2023-03-06) GIZACHEW MUSIE ALENBO
    The occurrence of floods as natural disasters has severe consequences worldwide, including loss of life, the spread of diseases, property damage, economic hardships, and social and psychological impacts on affected individuals. This study focused on modeling and analyzing the flood inundation and associated risks of the Akaki River, located in Addis Ababa, the capital city of Ethiopia. The primary objective of this study was to create models and maps that depict the extent of flood inundation and the risks associated with flooding events. To accomplish this, both primary field data and secondary data from various sources was collected. The materials utilized in this study included the HEC-RAS model, GIS software, GPS, and metering tape. The study involved conducting a hydrologic flood frequency analysis for different return periods, which served as input for flood inundation modeling and risk analysis. The HEC-RAS model was employed to develop flood inundation, flood hazard, flood vulnerability, and flood risk maps, which were subsequently mapped using ARC-GIS software. The results of the study revealed that the areas affected by floods varied depending on the return period. For return periods of 10, 25, 50, 100, and 200 years, the areas inundated by floods were measured to be 7.58 km², 9.79 km², 11.2 km², 12.45 km², and 13.83 km², respectively. The study also determined the maximum flood depths and velocities for each return period, with values ranging from 10.21 to 15.02 meters and 3.12 to 5.26 meters per second, respectively. Based on the flood hazard map for the 200-year return period, it was identified that approximately 13.7% of the total flooded area was categorized as an extreme hazard, rendering it unsafe for all individuals, vehicles, and structures vulnerable to flooding. Additionally, 17.6%, 16.7%, 18.9%, and 33.1% of the total area fell under the categories of very high, high, medium, and low hazards, respectively. The flood vulnerability map highlighted five levels of vulnerability, ranging from very low to very high. The very high and high vulnerability classes covered 9.59% (1.21 km²) and 15.54% (1.96 km²) of the flooded area, respectively. Furthermore, the flood risk was classified into five levels, revealing that 3.6%, 12.6%, 18.5%, 19.8%, and 45.5% of the flooded area were associated with very high, high, moderate, low, and very low risks, respectively. Considering the high risk and danger posed, particularly to residents residing in the flood buffer zone, a proposed solution to protect the area from flood hazards involved the construction of a 5.83 km levee embankment along the settlements on the left side of the river, specifically in areas with high population density. Finally, the performance of the HEC-RAS model was evaluated using model evaluation statistics, resulting in a coefficient of determination (R2) value of 0.94 for the water surface elevation, indicating a strong correlation between observed and simulated data. This study provides valuable insights into the flood dynamics, risks, and vulnerabilities associated with the Big Akaki River in Addis Ababa. The findings can inform decision-making processes aimed at mitigating the impacts of floods, protecting vulnerable populations, and enhancing overall flood management strategies in the area