Hydraulic Engineering

Permanent URI for this collectionhttps://etd.hu.edu.et/handle/123456789/69

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    FLOOD MODELING AND RISK MAPPING: (CASE OF KULFO RIVER IN SOUTHERN ETHIOPIA REGION
    (Hawassa University, 2024-10-22) CHALACHEW SHENKUTE
    Floods pose significant threats globally, causing immense damage to lives, societies, and economies. This study aimed to assess flood hazards, evaluate vulnerabilities, and determine flood risk along the Kulifo River floodplain. To achieve the objectives of a study, advanced hydrological and hydraulic modeling techniques were analyzed, using data from various sources, including rainfall from the National Meteorological Agency, stream flow data from the Ministry of Water Resources, and land use/land cover data from USGS. The HEC-HMS model accurately calibrated and validated using observed stream flow data, the result of model calibration gives Nash Sutcliffe efficiency (NSE) of 0.81, Percent Bias (PBIAS) of 1.77, coefficient of determination (R2 ) of 0.77, and Relative Mean Square Error (RMSE) of 4.28. During the validation period, the model gives (R2 ) of 0.79, NSE of 0.78, PBIAS of 1.09, and RMSE of 2.13. After model calibration and validation, flood hydrographs for different return periods were generated. These hydrographs served as inputs for the HEC-RAS hydraulic model, integrated with GIS software to map flood inundation areas. The resulting flood inundation maps revealed extensive flood-prone areas along the Kulifo River, with maximum flood depths of 15.2 meters and maximum velocities of 6.9 m/s during a 100-year flood event. Flood hazard maps classified areas into different hazard categories from low to extreme hazard, and 59% of inundated area falling under extreme, very high, and high hazard levels, 41% of inundated area falling under medium, and low hazard levels. Vulnerability analysis considered indicators such as flood depth, velocity, duration, slope, land use, and population density, highlighting 25% of the flooded area as very high and high vulnerability, 20% of the flooded area as moderate vulnerability and 55% of the flooded area as low and very low vulnerability. Combining flood hazard and vulnerability information, a comprehensive flood risk map was developed, identifying 32% of the flooded area as very high and high risk, 15% of the flooded area as moderate risk and 55% of the flooded area as low and very low risk. These high risk zones were concentrated in the Limat area of Arba Minch city, emphasizing the need for mitigation measures and emergency response plans. The flood risk map provided valuable insights for decision-making processes, guiding the implementation of structural and non-structural measures, floodplain zoning, and population relocation. This study's findings contribute to effective flood management, land-use planning, and disaster risk reduction strategies along the Kulifo River
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    FLOOD PLAIN ANALYSIS AND RISK ASSESSMENT ON ABELA-ABAYA FLOOD PLAIN AREA IN BILATE RIVER
    (Hawassa University, 2020-03-06) SWAT, iRIBB, iERDAS14, iSWATCUP, iRCP
    Flood is the most devastating extreme events across the globe. The floods phenomena are common in Abela-Abaya flood plain in Chokare and Guricho Kebele in the course of Bilate River. The main objective of this study is to conduct the flood plain and flood risk assessment in the flood plain Abela-Abaya area. Different input data were gathered and analyzed. Rainfall and air temperature data for a period of 1980 to 2015 were analyzed for characterizing the climate in the area. The streamflow data for a period of 1980 to 2015 was checked by stationarity and independence for input of unsteady process of HEC-RAS. Spatial inputs digital elevation model with a resolution of 12.5*12.5 m and land use map with a resolution of 30m * 30m were used for the HEC-RAS 2D model. Various methodological approaches were employed to achieve the objective. The easy fit software tool was used to identify the parent probability distribution which best fit the stream flow time series. HEC-SSP was used to compute the flood magnitude for various return periods. The HEC-RAS 2D 5.0.7 model was used to model the flood inundation depth, extent and velocity for various return periods in the flood plain area. Flood hazards are estimated based on flood depth, duration and velocity. Vulnerability index analysis was done from Questioners. Flood risks are then computed as product of flood hazard and vulnerability of different location in flood areas. The result of the frequency analysis show that the Extreme-Value Type I (Gumbel) best fitted the time series as evidenced through the goodness of fit statistics. Consequently the estimated quintiles for 2, 5, 10, 25, 50, and 100 years return periods were found to be 104, 156, 195, 252, 292 and 338m3 /s respectively. The HEC RAS 2D model from RAS Mapper showed that the 2, 10, 25, 50 and 100 years return period flood magnitude inundate about 674, 726, 752, 783, 804 and 998 ha of land. The relation between flood velocity and flood depth indicates that 79.2% is in ranges of medium to high hazard level and the other relation between flood duration and flood depth shows that 65% is in long-duration with a higher depth value. The map illustrates that most of the agriculture land and rural settlements area are in moderate risk ranges. The total crop loss for 100years flooding is 233,871.1 quintal and damage cost is 901,584$. To reduce the impact of risk a structural measures such as levee and drop structure are recommended along the river reach to safely pass the flood into the river.