Hydropower Engineering

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    Hydraulic Modeling and Flood Mapping Of Fogera Flood Plain: A Case Study of Gumera River
    (Addis Ababa University, 2012-03) Brhane Hagos; Yilma Sileshi (PhD)
    Nowadays, extraordinary floods are common many parts of Ethiopia causing a lot of losses to human lives as well as damage to property. Historically, Fogera/Dera flood plain has been vulnerable to flash flooding from rainfall, in particular of the Gumera catchment which passes in between the Fogera -Dera weredas. The tributary rivers are originating from the southern highlands of Debretabor with a steep slope. The Fogera –Dera flood plain is located east of Lake Tana in North West Ethiopia about 625 km from the capital city Addis Ababa and the terrain is fairly flat. The Gumara catchment drained by Gumara River is part of Nile basin The over flow of the river affects part of the Fogera /Dera flood plain but mainly the Fogera part at lower reach near to Lake Tana. Hence, this thesis is to identify peak flood and delineate and produce flood inundation mapping areas that can be affected by extraordinary floods and to recommend mitigation measures. This thesis tries to consider more options and fills the gaps not covered by others, adopting more than seven application soft wares like Arc GIS, Global Mapper, HEC-HMS, HEC-DSS, HEC-GeoHMS, HEC-RAS and HEC-GeoRAS. 30m*30m resolution DEM for the catchment and 2m contour interval for Fogera flood plain are used to analyze terrain information. For precipitation modeling, the daily rain fall basis is used for HEC_HMS calibration and ERA Intensity-frequency-duration curve is used for frequency storm analysis. The hydrologic frequency model is used for determining the peak flow discharge for return periods of 2, 5, 10, 50 and 100 years and the result is found to be 197.7m3/s, 246.8 m3/s, 265.4m3/s, and 306.0m3/s and 319.60m3/s respectively. For the 100 year flood frequency the maximum depth of flood is 7.94m and this depth of flood is extended to the flood plain up to 10km of the flood area which affects mainly the Wageta, Kidist Hana, Shina, Quhar Michael and Bebeks Tana mistily and Jigna Weredas .The total area affected by this flood is31.36 km2 and the area affected by the 2year flood inundation of 7.36m is 22.27 Km2.
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    Optimization of Hydropower Plant Expansion Case Study: Nile Basin, Ethiopia
    (Addis Ababa University, 2008-06) Jalele Geletu; Zelalem Hailu (PhD)
    This research is of a sequencing expansion problem in which capacity can be added only at discrete points in time. There is a forecast of demand in each period, and five expansion projects each with a given capacity and cost. Dynamic programming is used to determine the sequence of expansions necessary to provide sufficient capacity to meet the demand in all periods at minimum discounted cost. The alternative scenarios are represented with a tree structure. This research also provides preliminary results for a discounted cash flow as well as a dynamic programming solution.
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    The Techno-Economic Feasibility Analysis of Integrating Wind Power Pumped Hydro-Storage System to the Existing Hydroelectric Power Plants in Ethiopia (Case of the Koka Hydropower Plant)
    (Addis Ababa University, 2013-02) Mebratu Adamu; Tesfaye Dama (PhD)
    This thesis is intended to study the Techno-economic feasibility analysis of integrating Wind Power Pumped Hydro-Storage system to the existing Hydroelectric Power plants in Ethiopia specially to enhance the volume and efficiency of the Koka Hydropower Plant Station Reservoir by pumping water from the lower reservoir to the upper reservoir in order to supply reliable and steady water to the turbine. In the analysis five tasks are carried out these are: the critical months that are mainly affected by evaporation and climate change are verified which are March, April, May, June and July, the amount of the water that evaporates from the reservoir per hour is determined by using the Evapo-transpiration calculation technique which is the Penman-Monteith equation with heat storage and it is a method with strong likelihood of correctly predicting ETO in a wide range of locations and climates, by using this method the average hourly evaporation for these five critical months becomes 24,112m3/hr, the cost of a pipeline and the various components that contribute to the economics of pipelines for the study area is carried out including designing a fluid distribution system which is sizing of pipes and ducts, determination of the pressure drop in the system, and the power needed to pump required water to the upper reservoir, Wind energy and turbine investment cost analysis using RETScreen Software, and the economic analysis which is seen from three different perspectives that are: the integration of wind power pumped hydrosystem from the point view of energy security of the Koka Hydropower Plant, the profitability of the wind power used for pumping purpose from the hydroelectric power or the grid power pumping system, and the profitability of wind power used for pumping purpose from the diesel generator power pumping system. Finally from the point view of energy security of the existing Hydropower plants in Ethiopia the integration of the wind power pumped hydro-storage system is the best solution.
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    Modeling of Tekeze Hydropower Reservoir Operation with HEC – ResSim
    (Addis Ababa University, 2012-04) Mebrahtom Gebremariam; Bayou Chane (PhD)
    The main purpose of this study is to model the optimal operation of Tekeze hydropower reservoir for generation of energy and downstream water demand activities considering different scenarios on the power units by accurately determining the reservoir inflow using HEC-ResSim model. The main input data to the model; reservoir physical characteristics, operational characteristics, total monthly irrigation water requirement at downstream of the dam and the hydrological inputs to the reservoir (net evaporation, surface inflow to the reservoirs) are collected and configured. Tekeze dam is located about 80 km west of Mekelle city at coordinates 13° 21‟ North and 38° 45‟ East. To model Tekeze hydropower plant, simulation is performed under three scenarios: (i) the four Francis turbines units are operational, (ii) only three units are operational and (iii) only two units are operational. For each simulation three alternatives are defined on the gate arrangement of the low level outlets to obtain the best alternative that can generate maximum energy. Taking the best alternative, the simulation give for scenario one an average energy of 3669.8MWh and a maximum energy of 7200MWh, for scenario two an average of 3770.7MWh and a maximum energy of 5532.1MWh and for scenario three an average of 3278.1MWh and a maximum of 3641.2MWh. The reservoir level will be almost full in second and third scenario while in the first scenario reservoir level will be below the minimum operating level in the dry season. However, a unique reservoir operation rule curve and power guide curve as operated with the proposed model is developed in this study. Due to the regulation of flow in Tekeze dam, 70.5% in scenario one, 75.5% in scenario two and 81.3% in scenario three of flood occurred in the rainy season is retained by the construction of the dam. Therefore, there is a smooth release throughout the year. Hence irrigation development is possible in the lowland areas of Tekeze which has a total of 42965 hectares net irrigable area. Accordingly the minimum monthly power plant release 58.0m3/s, 98.1m3/s and100.6m3/s when all the four units, only three units and only two units are operational respectively is greater than the monthly peak irrigation demand (45.5m3/s). Therefore irrigation can be developed without affecting power generation to shorten the payback period of the dam and to increase the national economy.
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    Reservoir Operational Planning of Irrigation Dams for Micro-Hydropower Development (A Case Study Conducted on Haiba Micro-Irrigation Earth Dam in Tigray Regional State)
    (Addis Ababa University, 2005-09) Mulatu Tiruneh; Zelalem Hailu (PhD)
    Modern forms of energy are simply not available in rural areas of Ethiopia, while traditional sources such as fuel wood, cow dung, and crop residue are being depleted rapidly thereby deepening the rural energy crisis. Compared with other new and renewable sources of energy, micro-hydropower has been recognized as being a viable and mature technology. It can be applied immediately on an economic scale in a flexible manner and can comparatively easily bring benefits to the population in isolated areas, who are so far not covered by national electricity supply grid. About 84 percent of the Ethiopian people reside in rural areas and less than one percent of this population has access to electricity. However, a number of micro- irrigation dams have been constructed and planned for implementation, especially in Tigray and Amhara Regional States which could generate and provide electricity to the local population. A case study regarding reservoir operational planning had been conducted on Haiba dam, which is one of the fully implemented micro-irrigation earth dams in Tigray Regional State so as to integrate it with micro-hydropower. Accordingly a number of objectives were accomplished like formulation of discrete dynamic programming model, collecting, processing and analyzing meteorological data, collecting and preparing input data for the DP model. A Visual Basic Program was written to solve the DP model. The main results obtained were monthly energy output, energy output duration curve and optimal reservoir operation guide curve. The optimal power output of Haiba reservoir has an electrification capacity of 50 to 650 households each using one light bulb of 40w each. The results of this study showed that it is possible to produce a valuable amount of electric energy that is very useful in electrifying the rural community, from micro-irrigation dams without affecting its irrigation service by applying systems engineering as a planning tool. Based on the findings, conclusions and recommendations for further studies are drawn
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    Optimization of Small Hydropower in The Abbay Basin
    (Addis Ababa University, 2004-09) Tamene Adugna; Zelalem Hailu (PhD)
    Although Ethiopia possesses a huge hydropower potential, the energy problem in the country is enormous. A great majority of the population in Ethiopia are dependent on traditional resources to fulfill their energy needs. Due to the poor energy supply, the people not only have to put up with an unattractive living environment but also suffer the consequences of climatic change caused by the associated environmental impacts. Numerous villages do not get electricity supply due to the scattered nature of the settlements. Therefore, the energy policy should give enough attention to decentralized systems in which small hydropower potential plays a significant role. This study considers some of the small hydropower sites in the Abbay basin and that the selection of optimum sites or the optimum level of development at the sites can be undertaken with the application of non-linear optimization techniques. The optimization has been conducted on the basis of four theoretical small hydropower systems established in the Abbay basin. Among these four, the two systems consisted of two hydropower alternatives each and the other two consisted of three hydropower alternatives each. In this thesis, Microsoft Excel 2000 solver, which uses the Generalized Reduced Gradient(GRG2) algorithm for optimizing nonlinear problems has been used. Using this optimization technique, the level of development of each of the hydropower sites has been determined. The method can also be used to select the optimum small hydropower site(s) from a number of alternatives. Further study for optimization can be conducted on renewable hybrid systems combining a decentralized energy sources for rural electrification.
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    Performance Assessment and Upgrading of Walga Micro-Hydro Power Station
    (Addis Ababa University, 2017-07) Teklu Bekele; Edessa Dribsa (PhD)
    This research deals with the performance assessment and upgrading of Walga micro hydro power plant owned by government and fitted with cross flow turbine. Walga site is located in Oromia Regional State, South West Shoa zone, Wonchi Woreda Azer_Keransa Kebele. Walga site is located in a remote area. Currently, even though the village has the opportunity to get power from micro hydro power plant that was installed in 2014 by the Ministry of Water, Irrigation and Electricity, still the plant lacks reliability, sustainability and safety problems. The key reasons for the performance assessment and up grading of the existing Walga micro hydro power station were to know the efficiencies (turbine and unit efficiencies) and to determine the electrical power output of the plant. And also to know the power demand gap between supply side from the existing micro hydro power generator and demand side obtained from the village power demand assessment during the field survey. Therefore, performance assessment and testing, power need assessment of the community, determination of the power gap between the supply side from the existing Walga micro hydro power station and demand side were the purpose of this thesis work. In this study, performance assessment of existing Walga micro hydro power station was carried out and performance indicators were identified. Based on the performance test results and the village power demand assessment findings, the power demand gap of Walga village was known., Two options were proposed to meet the power demand gap of the village. The first option is developing a PV/micro hydro hybrid power supply system and the second option is developing micro hydro resource existing at the site. System designing and modeling by using Hybrid Optimization Model for Electric Renewable software for the two options were done and the simulation results were presented. Based on the Hybrid Optimization Model for Electric Renewable software simulation results, the performance and economic evaluations of each system were presented. Option I is characterized by as initial cost 8,719,300 Birr ($379,100), operating cost 276,690 Birr ($12,030), total NPC 12,618,812 Birr ($548,644) and cost of energy 8.70/kWh Birr (0.378$/KWh). The second option (Option II) is characterized by initial cost 1,357,000 Birr ($59,000), operating cost 54,510 Birr ($2,370), total NPC2,125,269 Birr ($92,403) and cost of energy1.47Birr/kWh (0.064$/KWh). Finally, the performance evaluations and economic evaluations made for the option I and option II. From the evaluation results, option II was selected as better option to fill the power demand gap of Walga village.
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    Application of the Geomorphologic Instantaneous Unit Hydrograph Concept for Runoff Prediction in Ungauged Catchments
    (Addis Ababa University, 2009-10) Tsehaye Zeray; Semu Ayalew (PhD)
    This study was aimed at development of unit hydrograph by relating the geomorphological characteristics of a catchment with the basic characteristics of the catchment IUH through the concept of Geomorphological Instantaneous Unit Hydrograph (GIUH) to address the problem of predictions in ungauged catchments. Two conceptual unit hydrograph models, ED-GIUH model and the GIUH based Nash model, have been used in the study. The geomorphological characteristics including the Horton‘s ratios of the catchments were extracted using GIS software called ILWIS. DEM-hydro processing, a new routine developed in ILWIS, was used for the extraction of the geomorphological characteristics. The geomorphological characteristics of a catchment were related with the shape and scale parameters of the Nash IUH to derive the complete shape of the GIUH based Nash model. ED-GIUH was developed from geomorphological characteristics of the catchments and probability density function of travel time of rain fall excess to the catchment outlet. These two models were developed in four catchments in Abay basin with range of areas (185-670km2). The velocity parameter of the two models was calibrated using unit hydrograph ordinates developed through rainfall-runoff analysis and the optimum velocity was determined. The performances of the calibrated models were evaluated using error functions, namely, Nash-Sutcliffe efficiency (NSE), percentage error in peak discharge (PEP), and percentage error in time to peak (PETP) and the models were compared together with the observed average unit hydrographs. From the results of the calibration as well as verification of the models it was found that both models were adequately simulate the shape of the unit hydrographs of the catchments. The ED-GIUH was successful in capturing the peak discharge of the hydrographs but the Nash based GIUH model was better in simulating the time to peak as well as the shape of the unit hydrographs. The optimized velocity parameter of ED-GIUH model was related to the geomorphologic characteristics of the catchments. The linear equation, relating the velocity with the slope and longest flow path of the catchments under the study was found to be best fit. A validation test was carried out to check the reliability of the derived equation in an adjacent catchment which was not used in the calibration of the models and a reasonable result was obtained in four rainfall-runoff events. Finally, it is clear that the predictability of the developed velocity equation in the region will be improved if the number catchments included in the calibration of the models were increased.
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    Evaluation of Climate Impact on Omo Gibe Basin (Case Study of Gilgel Gibe III Reservoir)
    (Addis Ababa University, 2012-03) Yemsrach Bishaw; Yonas Michael (PhD)
    Global climate change is known to influence regional hydrology, through changes in patterns of precipitation, stream flow and other hydrologic variables. With several plausible climate change scenarios in place for future, it is important to assess the possible impact on water resources, arising out of such scenarios. Such an exercise involves projections of climatic variables (e.g., temperature, humidity, mean sea level pressure etc.) at global scales, downscaling of larger scale climatic variables to local scale hydrologic variables and computation of hydrologic risk for use in water resources planning and management. This research presents the results of a study on downscaling large scale atmospheric variables simulated with General Circulation Models (GCMs) to meteorological variables at local scale in order to investigate the hydrological impact of possible future climate change in Omo Gibe Basin (Ethiopia). Statistical Downscaling Model (SDSM) was employed to convert the GCM output into daily meteorological variables appropriate for hydrological impact studies. The meteorological variables (minimum temperature, maximum temperature and precipitation) downscaled from SDSM were used as input to the HBV hydrological model which was calibrated (R2=0.798) and validated (R2=0.804) with historical data to investigate the possible impact of climate change in the catchment. The results obtained from this investigation indicate that there is significant variation in the seasonal and monthly flow. The impact of climate change may cause a decrease in monthly flow volume up to 23.55% in the 2020s and increase up to 33.43% in the 2050s. In the main rainy season (June-September) the runoff will be reduced by 21.67% in the 2080s. Seasonal flow volume may show increase up to 18.72% in bega and 12.87% in Belg However Kiremt season show decrease up to 17.59%. The result from different scenario also indicates that the catchment is sensitive to climate change.
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    Grand Ethiopian Renaissance Dam Reservoir Operation Simulation using HEC-ResSim and its impact on downstream Hydropower Generation
    (Addis Ababa University, 2014-03) Zelalem Tesfaye; Yilma Sileshi (PhD)
    In this study, HEC-ResSim model was used to simulate operation of existing hydraulic infrastructure, and major irrigation schemes in the Eastern Nile river basin and the new hydraulic infrastructure (GERDP).The main objective of this research is to find out the extents of the impact to which the introduction of new upstream reservoir, GERDP, on downstream users of the Nile waters by using the HEC-ResSim reservoir simulation model. Repeated runs of the HEC-ResSim model were made using different filling and after filling of GERDP scenarios to compare the effect of GERDP under alternative operating policies. The computational algorithm in HEC-ResSim is divided in to three major components: (1) watershed setup, (2) reservoir network, and (3) simulation for Calibration, Baseline and Alternative (Dry, Wet and Average filling and after filling) phase scenarios. The methodology computes the required releases to limit storage to the capacity available based on the probabilistic properties of future flows, conditional to current stream flow conditions. The first setup was to simulate gaged flow routing without taking into account effects of development using the flow data of 1956 to 2003 and a good agreement was observed between simulated and gaged data at El-Deim, Khartoum, Dongola, Hassanab and Tamaniat stations. The correlation coefficient R2 values for those stations were found to be in good agreement and found to be more than 0.925 for each station. Following this, the model was configured to simulate the existing and proposed development intervention. The baseline development Scenario is considering only existing major water infrastructures (i.e. reservoirs) and major irrigation schemes in Sudan and Egypt for a period of 1956 to 2003. The simulation result showed that an average annual energy of 14,810.83GWh/year is produced by Roseires, Sennar, Merowe and HAD. The Alternative scenario development which includes during filling and after filling of GERDP, HEC-ResSim simulation, has discovered that long term effects of new upstream reservoir on the operation of downstream reservoirs. After filling of GERDP phase scenario simulation using flow data of 1956 to 2003, the simulation result showed that an average annual energy of 31,363.63GWh/year will be produced by GERD, Roseries, Sennar, Merowe, and HAD (111.76% increase than without GERD), the reduction of average annual energy by 395.41 GWh/year from HAD will be compensated by the energy produced by GERDP and Sudan power plants, which will increase the total energy produced by the whole Eastern Nile system. During the filling phase scenario simulation results showed that an average annual energy of 27,041.96 GWh/year, 25,695.48 GWh/year, and 31,213.61 GWh/year will be produced by the 5 power plants during Average, Dry and Wet filling Scenarios respectively and average annual energy production from GERDP will be 11,314.38, 8,974.19, and 11,925.61GWh/year for the respective sequence of filling years. An average monthly power of 1,625.46MW and average annual energy of 14,238.99GWh/year will be produced during normal operation of GERDP (i.e. after filling from 2019-2066 for 48 years). Due to upstream regulation (i.e. intervention of GERDP, in the upstream of the Eastern Nile river basin) there will be an increase in average monthly inflow downstream in the driest month of the year and the annual average reservoir pool level increase which result in increase of power head.