Hydraulic Engineering
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Item FLOODPLAIN MODELING AND MAPPING USING GIS & HEC-RAS ON DOWNSTREAM REACH OF DIJO RIVER, ALAGE, ETHIOPIA(Hawassa University, 2022-10-08) MEKA TIRA WUDAFlood is the most dominant common, continuously frequent and destructive natural disaster in the world. It causes loss of life and property, displacement of people, breaking of socio-economic activities and loss of fertile agricultural lands. Dijo River flood affects Alage ATVET Collage during rain seasons. The main objective of this research is to map the flood inundation area on downstream reach (Alage ATVET collage) of Dijo River. GIS 10.3, HEC-Geo RAS, HEC- RAS 5.0.6, excel 2016 and easy fit 5.5 software’s are used for this research. primary data’s (total station surveying data, field observation) and secondary data (Dijo and furfuro stream flow data and Manning’s n value) are used to conduct the research. Flood frequency analysis, pre-processing, processing/model execution and post-processing methods are used and got 101.22m3 /s, 164.6 m3 /s, 175.8 m 3 /s, 207.58 m3 /s and 227.83m 3 /s peak discharge for 2, 10, 25, 50 and 100- years return period respectively. 27 x-section cut lines are drawn on 4km river reach geometry, among these 55.6 % of the x-sections are severely flood venerable x- sections from all return period peak flood discharges and to both side of the river reach. The flood inundation area of 2, 10, 25, 50 and 100 years return periods were 5702, 8154.71, 8499.96, 9271.9 and 9851.84m2 respectively. This area includes both Alage ATVET collage and neighboring kebeles of the collage. Therefore, the responsible body makes remedial measures to control the flood like repair and increase the height of the exiting earthen dykes at upstream of alage Bera Bridge, construction of new dykes and levees at the chefe agricultural area, grassland area and desilting siltation-filled x-section, afforestation from upper watershed of the riverItem FLOOD INUNDATION MAPPING AND HAZARD ASSESSMENT USING GIS AND HEC-RAS MODEL FOR BILATE RIVER FLOOD PLAIN, RIFT VALLEY, LAKE BASIN ETHIOPIA(Hawassa University, 2023-10-08) TIGIST ABERAFlood is a natural disaster that occurs suddenly which runs from hilly land to low land area of river banks when runoff exceeds the capacity of the natural or artificial water conveyance structures. Currently, the hazard of flood is common in some parts of Ethiopia including Bilate watershed and cause heart breaking losses in terms of property and even human life in flat river flood plains due to elevation difference and climatic factors. The main cause of flood disaster vulnerability is due to unavailability of proper River and watershed management. Hence, the intended aim of this research is to carryout inundation mapping and hazard assessment of Bilate River flood plain. The required data for this analysis were, Digital Elevation Model, stream flow data, soil type and land use land cover map. These data were collected from Ministry of Water, Irrigation and Electricity in legal request. Hydraulic Engineering Center- Geographic River Analysis System was used to prepare RAS import file for steady flow analysis on Hydraulic Engineering Center-River Analysis System. Stream flow data was checked for outlier and consistency at different significance level using Grubbs and Beck (G-B) test and double mass curve method respectively. For flood frequency analysis parameter estimation of worldwide used distribution functions was done by three important parameter estimation methods such as: method of moment, probability weight method and maximum likelihood method. Best fitted Pearson type distribution function was selected by linear moment (L-moment), D-index and correlation coefficient methods. The estimated peak floods in Bilate at Tena Bilate gauging station for 5, 10, 25,50, 100 and 500 years return periods were 153.2, 193.2, 273.6, 395.3 and 335.9 m3 /s respectively, at Guder station 140.89, 195.79, 217.64, 244.98, 270.33, and 323.86 m 3 /s respectively and at Wera were also 70.31,88.46,108.54, 121.9,134.17 and 159.78 m 3 /s respectively . Mapping of flood inundation was processed with inter connection of GIS extension tool HEC-GeoRAS and HEC-RAS software. The flood inundations for 5, 10, 25, 50,100 and 500 years return period were 16658, 16930,17207,17381,17531 and 17828ha respectively. Flood hazard map were prepared by reclassifying depth grid and its area bounding polygon. Also an assessment of hazard level was done with integrating flood causative agent land use land cover map with hazard map prepared after post-RAS processing. Area inundated at very sever to moderate hazard was ranges between 4% to 10.3% and around more than 72% was low hazard area. Hence, the result of the level of hazard indicates that there is significant potential of flood and the consequence risk on livelihood in study area in significant to sever level. It is recommended that, the watershed management party or any stakeholder, should use this research finding to take appropriate measure and reduce flood disaster in the future