Hydropower Engineering
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Item Optimization of Hydropower Plant Expansion Case Study: Nile Basin, Ethiopia(Addis Ababa University, 2028-06) 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.Item 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.Item 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.Item 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.Item 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.