Hydraulic Engineering

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

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Start date: 2020

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    FAILURE INVESTGATION OF EARTH FILL DAM, THE CASE OF ZANA DAM IN AMHARA RIGEN, ETHIOPIA
    (Hawassa University, 2020-07-03) DESTAW GASHAW ALEMU
    construction of dams serves a number of purposes such as water supply, irrigation, hydroelectric power generation, flood control and navigation etc.Zana dam is anEarth Fill Dam which islocated on Zana River used for irrigation purpose. The main problem of this dam is seepage and downstream slope failure.To address this problem evaluate the current dam conditionofdetermination of seepage and slope stability by Geo-studio software and identification of downstream slope failure and seepage through the body of the dam were assessed . Analysisofseepagewasdoneusingseepage and slope analysismethods which integrate Geo-studiosoftwareof Seep/w and slop/wtoolsatnormalandcurrentpoollevelcondition, the study was conducted mainly based on the laboratory investigation of materials used for construction. The result demonstrated that there wasa material property gap between what was stated in the design report and actually used in construction. The amount of seepage generated from the analysis was found to be1.406*10-7m3/s/mhowever from the actual constructed was found to be1.683 *10- 3 m3/s/m.Accordinglyfrom slope stability analysis the factor of safety of=1.335 and FS=1.193 for the designed and constructed sections respectivelywhich were less than 1.5.On the other handusing the newly proposed embankment section and the material property analyzed the seepage quantity through the embankment body found to be = 2.9218x10-7 m3/sec/m and the minimum factor of safety of = 2.127 and 2.285 with steady state condition upstream and downstream slop respectively, and factor of safety of =1.963 for using both horizontal and vertical seismic action. Similarly the major finding of the cause of failure is absence of proper filter and drainage materials. Result of gradation analysis of both base and shell materialsdemonstrated thatD15 (shell) =3 mm & D85 (core) =0.2mm this resulted 0.6mm>0.2mm which yielded that there was piping or internal erosion of the base material. Consequently the maximum and minimum bounds of filter materials obtained were: D60min=0.5mm, D15min=0.1 mm, D5min=0.075 mm, D100max=75 mm, D90max=20 mm, D60mm=2.5 mm & D15max=0.5mm obtained.Thereforecheminefilter material design and provision is mandatory for the safe life of the zoned type earth fill dam.
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    EVALUATION OF THE IMPACTS OF CLIMATE CHANGE ON SEDIMENT YIELD FROM THE KATAR WATERSHED, CENTRAL RIFT-VALLEY BASIN, ETHIOPIA
    (Hawassa University, 2021-12-10) GELILA SAMUEL
    Climate change is one of the issues that, the world facing today including Ethiopia and it is anticipated that climate change will impact sediment yield in watersheds. The purpose of this study was to investigate the impacts of climate change on sediment yield from the Katar watershed in the Eastern Lake Ziway Basin, Ethiopia. Here, used the coordinated regional climate downscaling experiment (CORDEX)-Africa data outputs of Hadley Global Environment Model 2-Earth System (HadGEM2-ES) under representative concentration pathway (RCP) scenarios (RCP4.5). The analysis was performed in two future projection of 2030’s and 2060’s under the reference of baseline period of 1987-2017 with their RCP correction. After assessment of missing, quality and consistency of data; bias, the coefficient of variation and correlation were used to evaluate the systematic error of precipitation amount, the degree of precipitation variability and bias-corrected before serving as input to the impact analysis A Soil and Water Assessment Tool (SWAT) model was constructed to simulate the hydrological and the sedimentological responses to climate change. The model performance was calibrated and validated using the coefficient of determination (R2 ) and Nash–Sutcliffe efficiency (NSE). The results of the calibration and the validation of the sediment yield R2 and NSE were 0.65 and 0.61, and 0.66 and 0.65, respectively. Climate change output from this research shows that the watershed will get warmer in the future. Both minimum and maximum temperature of the catchment have an increasing trend by 1.04 0C for 2030’s and 2.04 0C for 2060’s for minimum temperature and 0.90 0C for 2030’s and 1.56 0C for 2060’s for maximum temperature. Also, average annual rainfall shows increase by 4.8% for 2030’s and 1.6 % for 2060’s. The results of downscaled precipitation and temperature increased in both future period under RCP4.5 scenario. These climate variable increments were expected to result in intensifications in the mean annual sediment yield of 41.1% and 8.9% for RCP4.5 by the 2030s and the 2060s, respectively. The average annual sediment yield were 398 ton/km2 and 307 ton/km2 for the 2030’s and 2060’s, respectively. From this study, the results show that the sediment yield of the watershed is likely to increase under climate change scenarios. This will help water resources managers make informed decisions regarding the planning, management, and mitigation of the river basins.
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    GROUNDWATER POTENTIAL MAPPING USING GIS AND REMOTE SENSING: A CASE STUDY IN WEYIB SUB-BASIN, GENALE-DAWA RIVER BASIN, SOUTHEAST ETHIOPIA
    (Hawassa University, 2021-08-12) ABDULGEFAR MUHIDIN MOHAMMED
    To fulfill the demand of a rapidly growing population in drought-prone areas with high rate of urbanization, identification and management of groundwater resources are required. In the Weyib Sub-basin, a search for an alternative source of water has been always a major issue. The current practice of groundwater potential zone (GWPZ) identification is time-consuming and uneconomical. Therefore, it is required to apply effective techniques for proper evaluation of groundwater resources. This study applied integration of GIS-Remote Sensing (RS) and Analytical Hierarchy Process (AHP) for mapping the GWPZ of Weyib Sub-basin, Southeast Ethiopia. For this purpose the physiographic, geology and climatic factors influencing GWPZ of the study area were characterized. The thematic maps of geomorphological landforms, lineament density, geology, rainfall distribution, drainage density, elevation, slope, LU/LC and soil texture were prepared. System for automated geoscientific analysis (SAGA) GIS, PCI Geomatics, Rockworks 16, IDRISI Selva and Surfer 17.1, were employed for landform classification, lineament extraction, rose diagram preparation, pairwise comparison of the factors and identification of groundwater flow direction, respectively. The AHP technique of Multi-criteria decision analysis (MCDA) was employed to determine the relative weight and influences of the thematic layers. Geomorphologic landform, lineament density, geology, and rainfall distribution were found to be the dominant factors sharing the highest weightage of 67%. A weighting overlay approach of GIS was utilized to overlay the thematic maps. The resulting GWPZ of the study area indicates five zones representing very high, high, moderate, poor and very poor GWPZ. The areal extent of very high and high GWPZ is 41 km2 and 2032 km2, respectively. Moderate, poor and very poor GWPZ covers 2088 km2, 252 km2 and 0.142 km2 areas. The particular direction of groundwater flow is towards the NE and SE, coinciding with the direction of surface water flow. It was controlled by NW-SE striking geologic structures. The delineated GWPZ map is verified by using the existing water point’s inventory data. It indicates a good prediction accuracy of 84%. Thus, the identification of GWPZ by using GIS and RS through AHP is reliable for conducting similar studies
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    IMPACTS OF LAND USE LAND COVER CHANGE ON RESERVOIR SEDIMENTATION (THE CASE OF RIBB DAM, IN LAKE TANA SUB-BASIN, ETHIOPIA)
    (Hawassa University, 2020-10-06) MEBRATU ESUBALEW ENGIDA
    Land use land cover (LULC) change is the challenge and continuous drivers of environmental change. Understanding the rate and process of change is, therefore, basic for managing the water resources and the environment at large. This study was intended to analyze the LULC changes impacts on sediment load from 2000 to 2018 periods, and select critical (hot spot area) sub basins and recommend best management practice for Ribb watershed of Lake Tana sub basin, Ethiopia. Both climate and hydrometric (flow and sediment) data were collected and analyzed over the period 1990 to 2018. Two time satellite imageries of the Land sat product (2000 and 2018) were used for land use change detection. The hybrid classification technique for extracting thematic information from satellite images were employed by using ERDAS model for classification of LULC. The Soil and Water Assessment Tool (SWAT) model was calibrated and validated to estimate sediment load of the watershed during the period 1992 to 2001 and 2002 to 2007 respectively. To manage the sediment load best management practices (BMP) as a scenario (filter strip, grassed water way and contouring) were implemented on 2018 LU map. The land use change detection result indicate that cultivated land has expanded from 66.87% in 2000 to 75.53% in 2018. Between 2000 and 2018 periods, it was increased by 8.66 %. The rate of increment during 2000–2018 periods were 608.915 ha/year. Similarly, settlement area had also increased by 2.09% from 2000–2018 periods. Similarly, shrub land and bare land also decreased at a rate of 412.868 and 227.651 ha/year, respectively, between 2000 and 2018 periods. Also the water body decreased at a rate of 1.593 ha/year between 2000 and 2018. The SWAT model result depict that the model give reasonable fit of sediment flux with observation during calibration and validation as evaluated with ENS ( 0.63 ) , R2 ( 0.67) and percent bias (17%) during calibration and ENS ( 0.58) , R2 ( 0.71) and percent bias of (12%) during validation period. Moreover, the severity of soil loss rate was increased with the average of 26.89 ton/ha/year from 2000 to 2018 LULC, which indicates that the management practice, was weak within the watershed. The BMP scenarios depict that filter strip was significant amount of LULC conversions practice and soil loss rate had occurred in the watershed from 2000 to 2018 periods, and expected to continue in the future. Thus, appropriate conservation and management practice are very much crucial to safe guard the life of the reservoir