Title: Modelling of Cascade Dams & Reservoir Operation for Optimal Water Use: Application to the Omo River Basin, Ethiopia

Transcription

1 . Teshome Seyoum Bachilor Degree in Agric-al Engineering, Alemaya University,Ethiopia, 1995 Work in Water supply & irrigation projects from Master Degree in Irrigation Engineering, Arbaminch University, Ethiopia, 2007 Work in Haramaya University as Lecturer & researcher since 2007 Associate Dean, Institute of Technology, Haramaya University, Nov 2009-April 2010 Student in the Department of Engineering Hydrology & Geohydraulics, FB14 Kassel University since June 2010

2 Title: Modelling of Cascade Dams & Reservoir Operation for Optimal Water Use: Application to the Omo River Basin, Ethiopia Supervisor Prof. Dr. rer. nat Manfred Koch December 15, 2011 Kassel, Germany

3 Outline 1.Background 2.Study Area 3.Objectives 4. Relevance of the research 5. Methodology 6. References

4 1. Background Over times in the last century, people took the decision to build a dam. Dams were built to provide water for irrigated agriculture, domestic or industrial use, to generate hydropower or help control floods (WCD, 2000). Hydroelectric power dams currently provide 19% of the world s electricity supply. Worldwide, water demands have roughly tripled since 1950, & dams have helped satisfy that demand. About half of the world s large dams were built primarily for irrigation & contribute directly to 12 16% of the global food production (WCD, 2000).

5 Background cont... In relation to constructed dams, Africa contains some of the world s largest dams (e.g., Owen Falls (Uganda), Kariba (Zimbabwe) & Aswan High (Egypt). (ICOLD, 2003). Furthermore, Ethiopia has 13 hydropower dams and out of these ten were completed & three are under construction. According to 2005 plan of EEPCo, when the 3 dams complete, the capacity of the hydropower will increase to the capacity of 3,125 MW which will satisfy the electricity demand of the country.

6 Background cont... On the contrary, dams have considerable influence on d/s river ecosystems, in many cases extending for hundreds of kilometers below a dam (Collier et al., 1996, McCully, 1996; Willis and Griggs, 2003). One of the current issue which encountered opposition from International River (IR)-People- Water-Life in the construction of Gibe dam III in Omo river basin in Ethiopia is the best example which many will expect catastrophic effect on the d/s users & ecosystem.

7 Background cont... To take account of this problem the WCD called for a more equitable distribution of the benefits to be gained from large dams & proposed the inclusion of all identified stakeholders in the planning & management of water resources stored in a reservoir (WCD, 2000). To achieve this, dams & reservoir operation must take into account the availability of the water resource in the basin, water uses u/s & d/s of the dam & must give consideration to political, organizational, social & environmental factors, as well as economic factor (McCartney & Acreman, 2001).

8 Background cont... Hence, new strategies for effective use of the water in the basin particularly in the Omo River basin will be needed for water development & management to avert water scarcities that could depress d/s users & damage the environment. A large share of water to meet new demands must come from water saved from existing uses through a comprehensive reform of water policy. Integrated management must be the primary approach to addressing sustainable water resources, both for subsystem & river basin level.

9 2. Study Area The Omo-Gibe River Basin is almost 79,000 km 2 in area The basin lies longitude 4 30'N 'N & latitude 35 0'E 'E, altitude of 2800masl. The general direction of flow of the river is southwards towards the Omo River/Lake Turkana Trough, a fault feature.

10 3. Objective of Research Main objective The purpose of this study is to model cascade dams & reservoirs operation in the Omo river basin to satisfactorily simulate the operation of dams & reservoirs for optimal water use. The traditional individual reservoir operation will be extended by networking the cascade dams & reservoirs, using the HEC-ResSim modeling environment.

11 Specific objectives The specific objectives of the proposed study are To simulate runoff & inflow to the reservoirs in the Omo river basin using the SWAT model. To develop & recommend optimal dam & reservoir operation rule curves for cascade dams & reservoirs, more soundly based on evaluating the feasibility of various reservoir operating alternatives. To evaluate the effects of various reservoir operating alternatives on either preventing flooding or avoiding precarious low flow at locations d/s of the reservoirs.

12 Hydrological & Hydraulic Situation in the Omo River Basin

13 GIBE-I Presentation FB

14 GIBE-II Presentation FB

15 GIBE-III Presentation FB

16 GIBE-IV Presentation FB

17 GIBE-V

18 . Lake Turkana

19 4. Relevance of Research Nowadays many dams are planned, designed & constructed on a main river or tributaries in the same watershed. In such situations decisions pertaining to any given dam are often made without consideration of the operation of the other dams in the watershed. Therefore, according to Bergkamp et al. (2000), interrelation or networking dams and reservoirs for maximizing the benefit & minimizing the negative effect of the system operation is required.

20 Relevance cont.. Moreover, evaluation & modification of the planning & management of dams & reservoirs were largely ignored & little attention was given to how dam & reservoir operation might be modified. The outcome of the study will provide tangible tools for the possible redesign of the operation & management of dams & reservoirs for an equitable distribution of water to different stakeholders in the basin. Presentation FB

21 Relevance cont.. As such the results of the study may also be used to resolve debates on the constructing dams. At the very end, the study results may bridge the information gap that presently still exists on the Omo River Basin, so that concerned bodies & policy makers will get new information to strengthen their decision.

22 5.Research Methodology 1. Data collection Data collection for SWAT model Data require to SWAT for daily stream flow computation are: Daily values of precipitation, max & min air temperature, solar radiation, RH, & wind speed. If data are not available for PCP and Temp, then these values will be generated to fill in gaps in measured records using Auto regression & Multiple Regression of R program. For solar radiation, RH, & wind speed, these values will be generated using WXGEN weather generator model of SWAT.

23 Methodology Cont Digital elevation model (DEM) of the basin Land cover/use of the basin Soil type & management aspects Other data like reservoir, ponds and wetland, depressions, etc.

24 Methodology Cont Data collection for Hec-ResSim model Data require for HEC-ResSim for flow-routing and reservoir modeling. These data include: Time-series data computed inflow and incremental local flow hydrographs from SWAT model, observed flow hydrographs, observed reservoir pool elevations, releases and associated computed reservoir inflows, Physical & operational reservoir data

25 Methodology Cont Rating curves at each stream gage location Reservoir regulation manuals Geo-referenced map files of the Omo River Basin including a rivers and stream map files Defining operational data includes specifying the operation zones or levels, rules that contain the releases for each zone, and a release allocation strategy that include how the releases will be allotted to the available outlets

26 2.Analysis of data and simulations Insertion of the hydrological, metrological & watershed characteristics in the data base of the models Organizing, pre-processing & analysis of the data based on the requirement of the SWAT & Hec-ResSim models Schematization & configuration of stream alignment & configurations of the projects Developing network schematic Describing the physical & operational elements of the reservoir model & analyze the alternatives

27 Analysis & simulations cont Configuration of simulation to isolate the output analysis, Simulation of the dams & reservoirs network, Evaluation of the effects of various reservoir operating alternatives on flooding at locations d/s of the reservoirs, Calibration & Verification of the model, Development of a model that represents the cascade dams & reservoirs, Delivery of optimal water use operational model for Omo River Basin and Interpretation of the results.

28 ResSim Module Concepts.

29 Summary Activities required to achieve the objective of the study have been accomplished according to the method set in the methodology. Some of them has been completed: 1.Data collection & preparation for SWAT & Hec- ResSim model 2.Delinating the river basin & alighnment of the differnet elements Ongoing activities are: 1.Collecting lack data for the models 2.Calibration & verfication of the models 3.Simulation of the different alternatives 4.Write up of the thesis

30 6. References Akter, T. & Simonovic, S. P., (2004). Modelling uncertainties in short-term reservoir operation using fuzzy sets and a genetic algorithm. Hydrological Science Journal 49(6): Arnold, J.G., Srinivasan, R.S., Muttiah, & J.R. Williams. (1998). Large area hydrologic modeling and assessment part I : Model development. J. American Water Resource. Assoc. 34(1): Arunkumar, S., & Yeh, W. W. G. (1973). Probabilistic models in the design and operation of a multi-purpose reservoir system.

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