Hydraulic Engineering

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

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End date: 2019Has files: Yes

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    ANALYSIS AND PRIDICTION OF METEOROLOGICAL DROUGHT USING STANDARDIZED PRECIPITATION INDEX: CASE STUDY OF EASTERN OROMIA
    (Hawassa University, 2019-02-14)
    Ethiopia is one of the most drought affected country in Africa and suffered from acute drought many time in recent years. The objective of this study is to understand the rainfall variation and conduct an in-depth analysis and prediction of drought for to Eastern Oromia. Standardized precipitation index (SPI) was selected to characterize drought condition in the region. Drought characteristics at a time scale of 2-month, 3-month, 6month and 12-month were computed separately for 22 selected rain gauge station. The most maximum drought characteristics at 2-month, 3-month, 6-month and 12-month time scales have been found in Hararegie over last 36 years (1979-2015). The spacial extent of drought and rainfall variation were determined from SPI and CV values computed separately for each rainfall have been interpolated between station in Arc view GIS environment. The rainfall variation shows that the rainfall over the study area is highly variable and increases from Arsi to East Harargie and in the recent last decade (2005-2015) the map of SIP-3 (Belg) shows that a spacial extent drought over study area was irregular and there were no period in recent decades (2005-2015) without drought at least mild drought and this shows that the area is vulnerable to drought. The maximum intensity of (5.33) was recorded at Fedis Station for SPI-3 (kiremt season) in a year 1996, maximum intensity of (4.04) was recorded at Kobo Station in a year 1985 for SPI-3 (Belg season), maximum intensity of (4.77 and 4.5) were recorded at Ticho Station for SPI-6 (both seasons) and SPI-12 (annual) respectively. The drought prediction was made until 2043, using the Representative Concentration Path way (RCP) 8.5 Scenario.on the basis of the drought index measured by SPI. From the analysis of the drought index through the RCP 8.5 Scenario, extreme drought intensity will be more likely to occur. The long-term forecast (12-month period unit) showed that extreme drought would occur severely at station Diksis Sude, Hirna and Adelle from 2035 to 2040 and need more attention for this area
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    EVALUATING THE STABILITY OF EMBANKMENT DAM BY INTRODUCING CONCRETE FACE ROCK FILL DAM (CASE OF LEGEMERA DAM SOUTH WOLLO, ETHIOPIA)
    (Hawassa University, 2018-03-13) JEMAL KASSIM MOHAMMED
    Design of an embankment dam is a vital issue from the standpoint of safety, economy, controlling seepage, and speed of construction. Concrete face rock fill dams (CFRDs) virtually impervious, resistant to erosion and aging, workable, shorter period of construction and small volume of construction material. It is very well suited when there is no ample amount of impervious material within economically feasible hauling distance and severe weather conditions during construction. This study was aimed at addressing biggest challenge of hauling distance of the impervious clay core material by changing earth fill dam with central clay core to concrete face rock fill dam in case of Legemera micro earth dam, found in South Wollo. Universally recommended standard values beside to primary and secondary data essential for the work has been used. GeoStudio 2012 software was used for stability, seepage and deformation analysis of the dams. Consequently, by using this software good result of safety factor has been found for concrete face rock fill dam with regard to stability of the dam during maximum pool level, steady state condition and end of construction. During steady state condition, the upstream and downstream factor of safety computed for the dam is 1.954 and 1.544 respectively. Likewise, at the end construction, the upstream and downstream safety factor is 1.824 and 1.59 respectively. The seepage is also reduced to values of 2.42 x10-6 m 3 /sec by implementation of concrete face rock fill dam. Economic analysis result similarly shows that, concrete face rock fill dam is more economical by saving 22,441,387.75 ETB due to fast rate construction of the dam independent of weather condition. Generally, application of CFRD can fulfill the basic requirement and minimum factor of safety under all loading condition, and dam of such types is seepage free
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    ESTIMATION OF RUNOFF AND SEDIMENT YIELD USING SWAT MODEL: THE CASE OF KATAR WATERSHED, RIFT VALLEYLAKE BASIN OF ETHIOPIA
    (Hawassa University, 2019-07-27) Dulo Husen
    Estimating of runoff and sediment yield at watershed level is important for better understanding of hydrologic processes and identifying appropriate measures to combat erosion. In this study, Soil and Water Assessment Tool (SWAT) was used to calibrate and validate a hydrologic component on Katar river discharges at Habura gauging station and predict the stream flow of Katar watershed. The objective of the study was estimating the runoff and sediment yield for the Katar watershed using SWAT model. Sensitivity analysis, model calibration and validation were also performed to assess the model performance. From the result of Global sensitivity analysis, twelve(12) highly sensitive parameters were identified, and coefficient of determination (R2 ), Nash-Sutcliffe (ENS) and percent bias (PBIAS) were used as objective function to evaluate model calibration and validation on the monthly basis, and it could simulate runoff to a good level of accuracy. The results obtained were satisfactory for the gauging station (R2 = 0.80, ENS = 0.6 and PBIAS=0) for calibration and (R2 = 0.6, ENS = 0.55 and PBIAS=1.2) validation period. The simulated runoff and sediment yield of Katar watershed was quantified and also the utmost erodible part of the watershed was identified and prioritized. Among all sub-watersheds, nine (9) sub watersheds were more vulnerable to soil loss and potentially prone to erosion risk, which was out of range of tolerable soil loss rate (18 tha-1 yr-1 ). Large area of watershed covered by Haplic Luvisols(high clay content) and agriculture is the dominant activities in area. The simulated mean of sediment yield and runoff loss from watershed for 26 years were 11 tha-1 yr-1 and 12.3 m 3 s -1 respectively. The result of the study could help stakeholders to plan and implement appropriate watershed management strategies based prioritizations of severity of erosion. In conclusion, the SWAT model could be effectively used to predict runoff and sediment yield and result of the study could help different stakeholders to plan and implement appropriate interventions strategies in the Katar watershed.
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    EVALUATION OF THE PERFORMANCE OF TRADITIONAL IRRIGATION SYSTEM IN DEGALUNA TIJO WOREDA, ARSI ZONE, OROMIA REGION
    (Hawassa University, 2018-03-25) Seyoum Tadesse H/mariam
    This study was carried out at Degaluna Tijo Woreda traditional irrigation scheme with the objectives of characterization of the scheme, evaluating the performance of scheme using XV selected performance efficiency indicators and analyzing water productivity in relations to water applied. In the highlands of Ethiopia, irrigation practices have long been in use since ancient times for producing food crops. It was low momentum irrigation development, whereas the developed irrigable land had not been irrigating as expected. The areas that had been to use accounts less than 20% of the total irrigable land. It was made by measuring canals capacity and efficiency, length of water flow. Performance evaluation of the scheme was made using selected performance indicators such as conveyance, application, storage efficiencies, and distribution uniformity along with the water productivity in terms of water use efficiency as well as external indicators. The result obtained showed that conveyance efficiency of 82.69%, 75.27 %, and 80.45%, respectively. In the field that application efficiency, storage efficiency and irrigation efficiency on economic eight farmers’ plot located on different ends of the command 49-58%, 42-60 % and 57-89% upper, middle and downstream irrigation scheme respectively. Regarding the output per area, Temela Gusha was better than other systems, but for the output per water supply the converse was true that is, Hobori was better than others were. The institutional arrangement was poorly to support the irrigation farm association and crop pattern trends with the crop water consumption. It observes that from time trend of remote sensing image environmental climate condition famine change rapidly accelerated from time to time
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    FLOOD MAPPING ON GREAT AKAKI RIVER IN ADDIS ABABA, AKAKI KALITY SUB-CITY
    (Hawassa University, 2019-07-08) BERHANU BALTA HADARO
    In recent years, the patterns of flood across all continents have been changing and becoming more frequent, intense and leading the people to face risks. Therefore, the risk should be investigated and quantified properly. The objective of this thesis was to develop flood inundation maps of Great Akaki river in Addis Ababa, Akaki Kality sub-city. Streamflow, digital Elevation model (12.5*12.5 m) resolution and land use data were used as an input for the RAS mapper in HECRAS model. The 2D-HECRAS and ArcGIS models were used for mapping the flood extent, depth and velocity for various return periods. The Mann-Whitney and Wald-Wolfowitz statistical tests were used to hydrological data test. The basic assumption in statistical flood frequency analysis for its homogeneity, independency and stationarity of the time series at 5% significance level. The Easy fit 5.0 software was used to fit and identify the parent probability distribution for the streamflow data. The frequency analysis result depicts that Log-Normal probability distribution with 3 parameters best fitted the flood time series. The estimated quintiles for 2, 5, 10, 25, 50 and 100 years return periods were found to be 210.29, 333.04, 453.16, 626.19, 769.75, and 925.41 m3 /s respectively. The 2D-HECRAS model output indicated that about 86,123,156,228,285, and 350 ha land has been inundated for an event of 2, 5, 10, 25, 50 and 100 years of return period respectively. The 100 years flood magnitude inundated about 78, 272 and 34 ha of irrigated command area, swamp area and population settlement respectively. Flood risk map was developed based on hazard and vulnerability indicators. A preliminary alignment of structural flood protection dike was identified with length of 1.5km at downstream and 0.5 km at upstream of bridge which would make 95% of the settlement area on the left bank safe. The study has shown that the middle and lower part the study area is more inundated than upper parts. Therefore, the affected areas were whether to be free of infrastructure development, investment and residence of people or construct flood protection structure in order to avoid the risk of flooding in the area especially closer to the Great Akaki River
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    HYDROLOGIC RESPONSE TO LAND USE/LAND COVER CHANGE IN THE GENALE DAWA RIVER BASIN, ETHIOPIA
    (Hawassa University, 2019-08-06) MARTA AYE YALEW
    Land use land cover change has been one of factors responsible for altering the streamflow of the watershed on the Genale Dawa river basin leading to impacting river flows. The study mainly focused on estimating land use land cover change on streamflow. Land use land cover maps of 1986 and 2013 were obtained from Ethiopian Mapping Agency. The maximum likelihood algorithm of supervised classification was used in ERDAS Imagine 2014 software tool. A physical based, semi-distributed hydrological model, SWAT was used to investigate the impact of land cover change on streamflow of Genale Dawa River Basin gauged at Halwen. Land cover change analysis has shown an increment of cultivated land from 9.5% to 17.6%, agriculture land 9.1% to 19%, and built up areas 5.2% to 14.4%, while a decrement in the forest area from 31.15% to 19%, and water body from 7.2% to 7%, shrub land from 15.9% to 8.2%, Wet land from 8.8% to 4.9% and Grass land from 13.2% to 9.6% between 1986 and 2013. The performance of the SWAT model was evaluated through sensitivity analysis, calibration and validation. The model was calibrated using flow data from 1990 to 2001 including 2 year warm-up period and validated using data 2002 to 2007. Both the calibration and validation result show good agreement between observed and simulated stream flow with NSE and R 2 values of 0.86 and 0.88 for calibration and NSE are 0.84 and 0.85 for validation. Sensitivity analysis has shown that the curve number is the most sensitive parameter that affects stream flow of the watershed. The result of this study indicated that the mean monthly stream flow were increased by 8.5% for wet season and decreased by 3% in the dry season over 30 year’s period. As a result it might be possible to conclude that for the catchments the impacts were significant. Therefore, it can be deduced that LULC impact for the study area might be the most sensitive than the propagated uncertainty on catchment flow.
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    EVALUATION OF IMPACT OF INTERNAL EROSION ON THE STABILITY OF DAM
    (Hawassa Inversity, 2019-07-10) KETEMA TESFAYE ADUGNA
    Embankment dams encounter several problems in terms of dam safety. One of those problems is called internal erosion. This phenomenon is brought by the movement of fine particles within the dam due to seepage forces. Internal erosion represents a complex combination of several mechanisms related to the failure or near failure of dams and levees. If the dam is not able to self heal, the eroded zones will increase which will eventually cause the dam to fail. Specially if the discontinuity such us concrete conduit is there in the dam embankment the probability of concentrated flow occurrence through the embankment body is increased. The dam selected for this study Arjo Dhidhessa rock fill dam is currently under construction by MoWIE, Due to regied structure embedded in the body of the embankment dam it is related to the problem of internal erosion within the core. The impact of this internal erosion is analyzed in this thesis with the use of Finite Element Method/Analysis (FEM/A). FEA models simulate the in-situ stresses in the dam and calculate the strength. It also enables the analysis of changing hydraulic conductivity and its effect on the overall effective strength due to changing pore pressure and seepage forces. The analysis using numerical methods was performed in the program PLAXIS2D and SEEP/W while limit equilibrium analysis was done in SLOPE/W. The calculation in PLAXIS2D was performed by using the Mohr-Coulomb constitutive model. The in-situ stresses are initially calculated using gravity loading since this is the preferred method on an uneven terrain instead of a K0-calculation. Then, through a set of phases in the program, zones where erosion is assumed to have occurred are changed. These zones have a higher permeability and will thus affect the pore pressures in the dam following Darcy’s law with permeability through a set medium. The increased permeability is set to follow an increased void ratio due to loss of fine material in the core. How this increase of void ratio affects the permeability is investigated through using Ren et al. (2016) proposed equation for calculating permeability with a set void ratio. Their equation, apart from the usually used Kozeny-Carman equation, considers both effective and ineffective void ratio where the ineffective void ratios refers to the volume of pores that is immobile when flow is considered. Conduits through embankment dams are prone to seepage and internal erosion around the surrounding soil. The increased flow in the eroded zones of the core did not seem to impact the strength of the dam in much regard. The phreatic surface and thus the pore pressure did not change enough to influence the overall effective strength of the dam. It raises the question if the stability of an earth-rock fill dam will be affected due to increased pore pressure at all due to its draining properties and if it would rather fail due to increased seepage forces. Throughout design and construction of rockfill dam as much as possible fixing the conduit out of the embankment dam is recommendable to avoid the probability of concentrated flow which potential cause internal piping
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    EVALUATION OF PROPOSED EMBANKMENT DAM FOR DODOTA IRRIGATION PROJECT
    (Hawassa University, 2018-08-10) DAWUD MANZA DOLLEMO
    Design and construction of embankment dam is increasing from to time in our country to help the utilization of water for multipurpose. Evaluation of propose embankment dam for Dodota Irrigation project as alternative design by introducing asphaltic concrete core or clay core vital form the stand point of safety, controlling seepage and very important structure in fault and Earthquake area. This study was aimed to evaluate a proposed embankment dam as alternative design and analysis for Dodota Irrigation Project. Address this objective proposing an embankment dam with an impermeable asphalt concrete core and analyzes it for seepage static and dynamic stability using Geo Studio 2012 numerical computer program. Based on computation the flux through the dam and foundation for asphaltic concrete case has been found to be 0.000059 m 3 /s and the flux through the dam and foundation for asphaltic concrete case has been found to be 0. 0.001334 m 3 /s. The factory of safety of the propose embankment dam for the alternative design of embankment at different construction stage and with different loading condition satisfied the minimum requirement of (USAC,2003). The stress deformation observed was much lower than the expected bearing capacity of the foundation rock. The static deformation analysis computed for the propose embankment dam shows the horizontal and vertical deformation that the dam may subject to were in the tolerable limit. The dynamic deformation also analysis computed for the propose embankment dam during the time of shaking the maximum vertical and horizontal deformations within allowable limit. Generally, application of asphaltic concrete core rick fill and rock fill clay core dam in the project can fulfill the basic requirement and minimum factor of safety under all loading condition. Over all analysis of the thesis aim is indicate the possibility of constructing dam for the Dodota Irrigation Project