A THESIS SUBMITTED TO THE DEPARTMENT/FACULTY OF HYDRAULIC AND WATER RESOURCE, INSTITUTE OF TECHNOLOGY, SCHOOL OF GRADUATE STUDIES, ARBA MINCH UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN HYDRAULIC ENGINEERING.

Abstract

Climate change is exacerbating the frequency and severity of floods in catchment areas, leading to increased inundation and posing significant challenges for flow predicting. The impact of climate change on flood inundation and flow forecasting in catchment areas, highlighting the need for accurate modeling techniques such as HEC-RAS to assess flood risk, design resilient infrastructure, and develop effective emergency response plans. The study emphasizes the importance of integrating climate change projections into flood modeling to enhance preparedness and adaptation strategies in the face of a changing climate. This study aims to develop flood forecasting and inundation mapping under climate change for the Dijo River basin in the Rift Valley region of Amba Alage, Ethiopia. To simulate flood patterns and map potential inundation areas hydrological and hydraulic modeling for calibration and validation of observed flow to simulated flow, Improved CMIP6 models for better data assimilation methods, accurate and consistent projections of how flood inundation will be affected by climate change under the SSP2-4.5 and SSP5 8.5 scenarios for the baseline (1985-2014), mid-term (2041-2070), and long-term (2071 2100) cycles of the three climate models were used. Also, the General Extreme Value method was used to analyze the frequency of floods under both scenarios of SSP2-4.5 and SSP5-8.5 for 50 and 100-year return periods. The results of performance parameters R2 = 0.65, Pbias = 6.5, RMSE = 0.39, and NSE. = 0.65 for calibration and the R2 = 0.69, Pbias =7.4, RMSE = 0.41, and NSE. = 0.69 for validation. The peak flow of 50 and 100-year return periods in the long-term period under SSP2-4.5, and SSP5-8.5 respectively are 132.44, 154.32, 149.66, and 165.35m3/s. The flood inundation areas of 50 and 100-year return periods in the long-term period under SSP2-4.5, and SSP5-8.5 respectively are 83, 88, 90, and 94 ha. The maximum average flood depths of 50 and 100-year return periods in the long-term period under SSP2-4.5, and SSP5-8.5 respectively are 2.88, 3.12, 2.96, and 3.2 m. The responsible body deal with the remedial measures to control flood inundation under various climate scenarios, and also, the repairing and increasing the height of the existing earthen dykes, construction of new dykes and levees at the Chefe agricultural area, afforestation from the upper watershed of the Dijo River.