Hydraulic Engineering

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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
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
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
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
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
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
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.
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.
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.
DAM BREACH ANALYSIS AND DOWNSTREAM FLOOD MAPPING USING HEC-RAS AND HEC-FIA (A CASE STUDY OF GERHU-SIRNAY DAM)
(Hawassa University, 2020-07-03) KEHASE NEWAY GEBRETSADKAN
Dam breach analysis is a science that quantifies the hazard sourced from dam failures. On downstream of Gerhu-sirnay dam there are developments including water treatment plant and multi owner seasonal agricultural areas. The objective of this study was to estimate breach outflow hydrograph to the downstream reach for overtopping and piping scenarios henceforward to assess flood damage for the worst scenario. The quality of rainfall data was tested for outlier, adequacy, homogeneity using Pettitt (1979) test and consistency tests. The probable maximum precipitation calculated by Hershfield (1965) method was 129.7 mm. The inflow hydrograph was obtained by using soil conservation service (SCS) method and its probable maximum flood (PMF) reaches 329.1 m 3 /s. The breach parameters for both scenarios were early calculated by the four regression equations integrated with Hydrologic Engineering Center River Analysis System (HEC-RAS) breach calculator tab. Due to comparison in both scenarios, the final breach parameters were taken from Von Thun and Gillette (1990). For overtopping the resulting parameters were 54 m breach bottom width, 85.75 m breach top width, 0.5 side slope (H: V) and 0.73 hrs breach formation time whereas in case of piping these parameters were 32 m, 57.75 m, 0.5 and 0.53 hrs respectively. Then HEC-RAS version 5.0.3 has used to model the dam breach analysis with two dimensional unsteady flow conditions of inflow hydrograph as upstream boundary condition and normal depth as downstream boundary condition. The peak breach outflow for both scenarios were 2,239.7 and 1,282.68 m 3 /s respectively as overtopping was the worst scenario. From the prepared inundation maps by GIS for about 521.1 ha area was inundated under the worst scenario with a maximum depth 24.07 m and duration of 1.0 hrs. By using Hydrologic Engineering Center Flood Impact Analysis (HEC-FIA) version 2.2, the flood damage was estimated in terms of direct economic damage and life loss. The total ex-ant direct economic damage result shows 63,650,493.3 Birr. From the report of LIFE-Sim dynamic model integrated with HEC-FIA, about four persons could be lost their life. To minimize the quantified damage, well operation of emergency action plan would be an important tool. The water treatment plant of Gerhu-sirnay town must be displaced from its current place to at least 0.073 km apart from both sides of the river banks until to do this the stakeholders of the plant must be under the age of 65 years to have an efficient warning mobilization
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.
ASSESSMENTS OF SUITABILITY OF CONSTRUCTION MATERIAL WITH SPECIAL EMPHASIS ON FILTER: - THE CASE OF AGUAT WUHA EARTH DAM AT
(Hawassa University, 2020-07-10) HENOK DESSALEGNTILAHUN
Aguat-wuha dam is an earth fill dam, which is one of the Irrigation Projects undertaken by AWDSE found in South Wello Zone, Sayint Ajibar Woreda. As it was observed, during the construction process the construction material, the filter material in particular, was not properly prepared while placement. This could result in malfunctioning of the filter zone as a because of material poor gradation and contamination. Hence, this work was aimed to evaluate the suitability of construction material especially on filter material assessments. During this research work materials for analysis were taken from the dam which is on construction and filter material samples stored in stoke. The geometrical criteria have been mainly checked using the formulas and recommendations proposed by scholar and standard. In addition to this, the final gradation or grain size distribution of a suitable filter material has been prepared based on the gradation of the base material following the design procedures prepared by USSCS and Sherard recommendations. It was found that the filter material taken from the dam and analyzed for grain size distribution doesn’t satisfy most of the filter criteria. On the other hand the treated sample of this same filter material showed better in satisfying most of the filter criterion and also the stocked filter material was contaminated due to improper placement and poor prevention. The analysis result (especially USSCS method) indicated that the treated (washed) filter material almost satisfies the geometrical criteria and it had a little bit fine (1.7-2.2 %.), which was still in the limit of the filter band. On the other side, the constructed sample was not satisfied the gradation curve. Because it was over fined, that 5.5-5.8% passes the fine limit of filter which can result clogging, poor permeability, weak draining capacity and crack for coming serviceability. Additionally the material contamination result shows, mostly on the underneath of stoke especially from ground to 80 cm because the material was near to unexpected runoff entry. Therefore the field manager or site engineer should apply efficiency checking and giving remedial measure carried out not only at quarry site but also during construction. Additionally design of quality control and quality assurance should properly apply
LAND USE LAND COVER DYNAMICS AND CLIMATE CHANGE IMPACT ON THE HYDROLOGY OF RIBB RIVER CATCHMENT, UPPER BLUE NILE BASIN, ETHIOPIA
(Hawassa University, 2020-10-06) SAMSON iHAILE
This iinvestigation iexpects ito iassess ithe ieffects iof iclimate iand iland-use ichange ion ithe ihydrology iof iRibb iwatersheds iusing ithe iSoil iand iWater iAssessment iTool i(SWAT). iRibb iwatershed iis ilocated iin ithe inorthwestern iEthiopia iRiver ibasin iwhich iextends ifrom i10.00ºN ito i11.00ºN ilatitude iand ifrom i35.00ºE ito i38.00ºE ilongitude. iThe iexamination idissected ithe ihydrologic ieffects iof iclimate iand iland-use ichanges iin itwo idifferent iways. iThe imain iperspective icomprises iof idescribing ihydrological ichanges itwo iverifiable iland iuse imaps i(Land iSat_8 i2001, i2017) iwere iutilized ito ispeak ito iland-use ichange ion ithe iwatershed, iand ihistorical iclimate idatasets i(1988-2017) iwas iutilized ito imake iSWAT imodels ifor iRibb iwatershed. iLand-use ichange irecognition iwas ifinished iusing iremote idetecting iprocedures iand ithe imaps iwere iprepared iusing iERDAS iImagine i14 iand iArc iGIS i10.3 isoftware. iClimate iand iLand iuse iis itwo iprimary ifactors istraightforwardly iimpacting ithe ihydrological iprocedures iof ithe iwatershed. iRCP i4.5 iand iRCP i8.5 iscenario iwere iused ito iproject ithe ifuture iclimate iof ithe i2050s, iand i2080's. iThe ianalysis iwas iperformed iin itwo ifuture iprojection, i2050 iand i2080 iconsidering ithe ireference ibaseline iperiod i1988-2017 iwith iboth iRCPs. iMaximum itemperature ichanges ifor iRCP i4.5 iraised iby i0.17°C ito i0.9°C iand i0.2°C ito i1.1°C, iand ifor iRCP8.5 i0.2°C ito i1.06°C iand i1.04°C ito i1.73°C iMean imonthly imaximum itemperature ichange ifor ithe i2050s iand i2080s. iand iMinimum itemperature ichanges ifor iRCP i4.5 iand iincrease iby i0.03°C ito i0.8°C iand i0.2°C ito i0.95°C iand ifor iRCP i8.5 i0.25°C ito i0.84°C iand i0.31°C ito i1.65°C ifor ithe i2050s iand i2080s itime iperiods iwith ireference ito ithe ibaseline iperiods irespectively. iAnd ialso, ithe imean imonthly iprecipitation ichange ishowed iincreasing i iby i4.25mm ito i6.25mm iand66.42mm ito i78.32mm ifor iboth iRCP4.5 iand iRCP8.5 iscenarios irespectively. iCombined iimpacts iof iland iuse iand iatmosphere ichanges iindicated ithat i88.15m3/s ifor ibaseline, i40.57 im3/s imore iin ithe i2050s, iand i38.48m3/s imore iin iThe i2080s ifor istream iflow icompared ito iclimate ichange iscenario. iThe icombination iof iclimate iand iland-use ichanges iwould ilead ito ia idecrease iin istream iflow i(73.55% ito i29% iin ithe i2050s iand i64.98% ito i14.67% iin ithe i2080s). iSWAT ioutput ito ibaseline irun i(1987-2017). iClimate iand ithe iland iuse iland/cover ichange iand iits imain iimpetus ion iRibb iwatershed iutilizing iLANDSAT_8 iimage ito icreate itwo ithe ihydrological imodel ioutcome ishows ithat ithe istream iwas itouchy ito iland icover ichange iby ilessening ibase istream iand iincrement itop istream ithis iis ibecause iof iincrement iagrarian iland iand ideforestation.
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
IMPACTS OF LAND USE LAND COVER CHANGE ON RESERVOIR SEDIMENTATION (THE CASE OF RIBB DAM, IN LAKE TANA SUB BASIN, ETHIOPIA)
(Hawassa University, 2020-10-21) 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
IMPACT OF CLIMATE CHANGE ON THE HYDROLOGY OF UPPER BLUE NILE RIVER BASIN: A CASE STUDY IN TANA SUB-BASIN, ETHIOPIA
(Hawassa University, 2020-11-06) SURAFEL ARAGAW LAMESGIN
Climate change is one of the serious issues in the word including developed and developing countries like Ethiopia. Tana Sub-Basin is located in the upper Blue Nile River basin . The aims of this study was to evaluate the impact of climate change on the hydrology of Upper Blue Nile River basin of Tana sub-basin in the northwest of Ethiopia. Dynamically downscaled climate model precipitation and temperature outputs were obtained from CORDEX-Africa program RCP4.5 and RCP8.5 by Regional Climate Model. The climate data has significant bias and bias correction was done by using CMhyd tool before used as input to the impact analysis. The analysis was performed in two future projection, 2020-2049 and 2050-2079 considering the reference baseline period 1988-2017 with both RCPs. Minimum temperature changes for RCP 4.5 raised by 0.26°C to 1.10°C and 0.45°C to 2.77°C, and for RCP8.5 0.15°C to 1.58°C and 1.02°C to 2.68°C Mean monthly minimum temperature change for 2020 – 2049 and 2050 – 2079. and Maximum temperature changes for RCP 4.5 and increase by 0.25°C to 1.6°C and 0.1°C to 1.91°C and for RCP 8.5 0.11°C to 1.92°C and 0.19°C to 2.17°C for 2020 – 2049 and 2050 – 2079 time periods with reference to the baseline periods respectively. And also, the mean monthly precipitation change will be increased and decreased by 2.09% to 23.95 % and 30.73% to 47.46% for both RCP4.5 and RCP8.5 scenarios respectively. The SWAT models were used to assess the streamflow response to climate change. Calibration and validation of the model output were performed by comparing simulated streamflow with observed flows from Tana Sub Basin (Blue Nile River outlet at Bahirdar gauging station) for the periods 1988-2001 for calibration and 2002-2008 for validation using SWAT-CUP(SUFI-2). The model calibration and validation result shows R2 and NSE of 0.87 and 0.84 and 0.61 and 0.6 during calibration and validation respectively. Finally, climate change impact on monthly streamflow was evaluated by relating base period stream flow with the future flows for the 2020-2049 and 2050- 2079 for both RCP4.5 and RCP8.5 scenarios. The future streamflow result shown increasing and decreasing change for both RCP4.5 and RCP8.5 scenarios. Hence, the increased and decreased stream flow in the basin may have a significant contribution for the sustainability of existed and undergoing water development projects
EVALUATION OF THE EXISTING URBAN WATER SUPPLY SYSTEM: A CASE OF HARGEISA CITY, SOMALILAND
(Hawassa University, 2020-12-17) MOHAMOUD MOHAMED ISMAIL
Urban water supply and demand challenges are widespread problems in most of the developing countries such as Somaliland. This thesis paper focuses on the evaluation of the existing urban water supply system of Hargeisa, capital city of Somaliland. The main objectives of this study is to spot the issues of Hargeisa water system by assessing the current status of the water supply system in the town, evaluating the Hydraulic performance of the WSS and eventually propose remedial measures. The current status was evaluated rely on the difference in the supply and demand of the town by forecasting its population while the water losses was used the difference between the production and consumption data. Moreover, to investigate the existing water supply and distribution system, an EPANET software was used to develop the model. The model can be used to customize the high pressure and low pressure zones in junctions and the level of velocity through pipe. The model run was performed for average, maximum, peak and low demand situations to investigate the system model. The analysis result shows that the supplied water in the town is only covering 13.5% of the demand. Hence, this result indicates that there’s a high gap between the demand & supply. In Addition, from three years obtain data of production and consumption the average loss became 9.75%. Moreover, the result and discussion shows that there are totally different issues of the system like high pressures and low pressure whereas, the utmost pressure occurred at gravity main pipe line in night demand was 85.92m which is above the suggested value and also in the low hour demand (LHD), 100% of the velocity in the pipes is less than 0.5m/s. To handle the problems, it needs providing extra pumps to increase the production, rehabilitate the prevailing well sources, maximizing the capacity of distribution pipe line by putting new pipes
HYDRAULIC PERFORMANCE EVALUATION OF CROSS DRAINAGE STRUCTURES (THE CASE OF BOKOJI TO KERSA ROAD, OROMIA REGION)
(Hawassa University, 2021-03-07) GOSA MICHAEL EDAO
Drainage problem is a major concern in the functionality of road. Raise in traffic interruption, structures damage and loss of life can be caused due to poor drainage. To cope with these problems, it is essential to determine the functionality routine of such structures through hydrologic and hydraulic investigation. The study attempted to analyze hydraulic performance of drainage structures found along Bokoji-Kersa road. Different datasets (spatial, hydrological, metrological, survey data) and models (SCS CN and HEC-RAS) were used. Arc-Hydro and image classification tools of ArcGIS, Easy-fit program, statistical methods (Gumble and Lognormal) are employed as processing tools to prepare model inputs. Watershed delineation, land use land cover classification, generation of IDF curves, peak discharge estimation, and steady flow simulation of water surface profile were the active tasks conducted in the study. It was found that the existing Katar Bridge has insufficient size even to convey 320.20m3/s peak design flow of 50 year return period. The resulted water surface elevation was 2496.82m, whereas the lower cord elevation of the Bridge is 2496m. Moreover, the hydraulic capacities of some drainage structures are adequate but inefficient. Limitations in the hydraulic and hydrologic investigation during the design and construction phase were identified as the cause of the problems. Subsequently, causes of gully erosion at the outlet and blockage by sediment led to reduced functionality, traffic interruption, and loss of propert
FLOOD RISK ANALYSIS FOR LOWER GUDER RIVER FLOODPLAIN IN RIFT VALLEY LAKE BASIN
(Hawassa University, 2021-07-06) DESTA USI AMBOMSA
River flooding is a natural process and part of the hydrological cycle of rainfall, surface and groundwater flow and storage. Floods occur whenever the capacity of the natural or manmade drainage system is unable to handle the volume of water generated by rainfall. Guder river catchment is found in South Nation and Nationality region in the upper rift valley. Guder flood plain has been frequently affected by flood events during rainy season. The main objective of the study is to assess flood risk in Gudar floodplain of lower Gudar River basin. The data used for this study was annual maximum flow data, DEM, land use land cover map, and soil map and surveyed cross sectional data flood frequency analysis of annual maximum flow data was analyze. Homogeneity and stationary tests at different significance levels were done using Wald-Wolfowitz and Mann-Whitney tests. Guder station was found to be independent, homogenous, stationary and no outlier at 5% significance level Using the method of goodness of test technique, the time series of the flow data was fitted to Log Pearson Type III. The flood frequency analysis method, HEC-RAS, HEC-GeoRAS and ArcGIS are used to determine the peak flood for different return periods and flood hazard map. The simulation result for return period of 5, 25, 50,100 and 200 year floods magnitude are 34.17 m3 /s , 67.92 m3 /s , 83.18 m3 /s , 102.82 m 3 /s and 122.32 m3 /s respectively. The maximum inundation depth (in m) the corresponding area coverage (in ha), and potential loss of crops in quintal are estimated to be 1.25 m/90.9ha/2,199.78 quintal; 1.733m/102.1ha/2,470.82quintal; 1.97m/ 114.6ha/2,773.32 quintal; 2.13m/ 122.8ha/, 2,971.76 quintal; and 2.37m /127.4ha/, 3083.08 quintal respectively with a maximum velocity of 5.95 m/s. Lastly the study shows that the lower part the study area is more inundated than the middle and upper parts specially those areas closer to the Guder River. Appropriate land use planning and soil conservation practice should be carried out in the upper catchment in order to reduce the magnitude of flood and siltation plus for regulated discharge of water at downstream area.
ESTIMATION OF SOIL EROSION AND SEDIMENT YIELD OF GEFFERSA RESERVOIR WATERSHED
(Hawassa University, 2021-07-10) KANAOL MERERA ABDISA
Sedimentation is an important parameter to measure the life of a reservoir. It depends on sediment yield and sediment yield depends on soil erosion. This study has been conducted in Geffersa reservoir watershed in the upper Awash River basin of Ethiopia. The objective of the study is to estimate potential soil erosion, sediment yield from the watershed and identify hotspot areas for proper planning using Arc GIS and RUSLE adopted to Ethiopian condition. The revised universal soil loss equation (RUSLE) was integrated with Geographic Information System (GIS) to model the spatial patterns in soil erosion in the watershed. All the parameters of the model (erosivity, erodibility, steepness, land use land cover, and supportive practice factors) were used in ArcGIS to create a soil erosion map. The annual soil loss of the watershed range from 0 to 728.48 ton/ha/year. The average annual soil loss value was found to be 23.6 ton/ha/year and has been classified into five erosion severities classes as very slight, slight, moderate, severe, and very severe to identify erosion hotspot area. Based on those results, 772.73 ha & 606.34 ha of the watershed were felt under severe and very severely vulnerable to soil erosion. The estimated Sediment yield delivered to the outlet was found ranges 0 to 78 ton/ha/year. The average annual sediment yield from the entire watershed is 5.3 ton/ha/year. If the same rate of sedimentation continues, the total storage volume will be filled up in 394 years. Out of the available reservoir sedimentation management strategies, watershed management is the best technique to minimize the sediment yield and its flow into the reservoir.