Water Resource System Modeling and Hydro-economic Trade-off Analysis of Abbay River Basin, Ethiopia
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Date
2024-08
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Addis Ababa University
Abstract
This study was aimed at analyzing the hydro-economic trade-off and synergy between water, hydropower, and irrigation in the Abbay River basin by considering multiple development scenarios. The study scoped in assessing the water potential of the basin and analyzing the trade-off and hydro-economic benefit between irrigation development and hydropower generation.
Multi-statistical performance criteria proved that the ArcSWAT model has the capacity to reproduce flows that agree with the measured flows and was found to be applicable over the Abbay River basin. The result revealed that the performance of the model improved as the basin was partitioned into sub-basins. The evaluation of different flow segments showed that the ArcSWAT model performed better for peak and high flows than mid and low flows. Overall, the model generates flow data that closely matches the measured flows in the Abbay River basin, which can be utilized as inputs to assess the trade-offs between hydropower and irrigation development.
The hydro-economic trade-off analysis was undertaken to provide insight regarding the benefits received from hydropower and irrigation development scenarios. The research demonstrated the holistic development of water resources for both energy generation and irrigation purposes, thereby maximizing economic benefits while ensuring sustainable water resource management. HEC-ResSim model was found to be adequate for evaluating the power generating capacity of multiple hydropower cascade systems under various irrigation water diversion scenarios. The findings revealed that by focusing solely on hydropower projects without incorporating irrigation development, the Abbay river basin would generate up to 38 TWh of annual energy from GERD, Karadobi, Bekoabo, and Mandaya cascades, with GERD accounting for 39% of the total output. Under full integration of irrigation development with four hydropower cascades, annual system energy generation was reduced by 12%.
The hydro-economic trade-offs between hydropower generation and irrigation development within the Abbay River basin. By analyzing various development scenarios, the study reveals how prioritizing one objective, either hydropower or irrigation, impacts the overall economic benefits. A key reference point is the absence of irrigation development, which serves as a baseline to assess the benefits of different scenarios.
The results demonstrate that as irrigation benefits increase, hydropower benefits decrease, and vice versa. For instance, with no irrigation development, annual benefits from a series of cascade hydropower projects range from $1.3 billion to $3.1 billion USD, depending on the number of projects However, expanding irrigation reduces hydropower benefits by approximately 5% for every unit increase in irrigation benefits.
When full irrigation development is achieved, annual irrigation benefits reach $3.6 billion USD, surpassing hydropower benefits by 17%. The analysis highlights that while trade-offs exist, pursuing both hydropower and irrigation concurrently results in greater combined benefits than focusing on either objective alone. The study concludes that integrated development of hydropower and irrigation within the Abbay River basin yields optimal economic outcomes, with combined annual benefits reaching nearly $6 billion USD, 94% higher than those from hydropower alone.
Assessing the long-term economic benefits of hydropower and irrigation development in the Abbay River basin, taking into account the variability in returns over time was another basic points addressed in this research. Four scenarios are explored, each involving different combinations of dams (GERD, Karadobi, Bekoabo, and Mandaya) and a consistent irrigation area of 1.2 million hectares.
The analysis shows a clear upward trend in economic benefits over time. Scenario 1, which includes only the GERD and 1.2 million hectares of irrigation, generates a present benefit of $4.5 billion USD, projected to rise to $26 billion USD by 2050. Scenarios with additional dams show progressively higher future benefits, with Scenario 4, incorporating all four dams and 1.2 million hectares of irrigation, yielding the highest returns of $34 billion USD by 2050.
The study underscores that while present economic benefits are modest, substantial gains are realized in the long term, particularly as more dams are added to the development plan. The findings suggest that comprehensive development of hydropower and irrigation in the Abbay River basin offers significant economic advantages, especially in the long run, with the full cascade of dams providing the greatest benefits. The study also revealed that simultaneous development of hydropower and irrigation is advisable rather than prioritizing hydropower projects exclusively over the Abbay River basin.
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Keywords
Abbay River, Trade-off, hydro-economic, Water potential