Abstract
Demand for fresh water, as one of the major natural resources, is increasing rapidly with increasing development and environmental degradation. The continued abstraction of water from Lake Ziway and its main feeder rivers Meki and Katar for irrigation indicates that the water demand may soon exceed the supply. To illustrate disparities in spatial distribution of water resources, the Upper Awash sub-basin, which shares a water-divide with the CRVL sub-basin, has large flow volumes particularly in the rainy season and suffers with seasonal flooding. The rationale behind regaining the water in CRVL relies on this non-uniform spatial distribution of fresh water, calling for a balance between water surplus and deficit regions. For this reason, Inter Basin Water Transfer (IBWT) is suggested as a viable option to augment utilizable water resources of the Upper Awash sub-basin to reduce the significant pressure on the water supply of the rapidly developing urban and irrigation areas in the CRVL sub-basin. A water evaluation and planning (WEAP) model was used to quantify the amount of surplus water in the donor basin, when examining the hydrological dynamics of the basins. Furthermore, optimal flow diversion scenarios were generated by maintaining two baseline scenario constraints. The estimated surplus water in the rainy season is expected to contribute 18 million cubic meters (mcm), 88 mcm and 192 mcm in months June, July and August respectively under average conditions. The optimal amount of diverted water could potentially stabilize the environmental degradation of Lake Ziway and Lake Abijata by compensating for development-driven abstraction and surface water evaporation respectively.
Highlights
Ethiopian water bodies, the Central Rift valley Lakes (CRVL), have been faced with changes like water level reduction, land degradation, and overutilization [1]
To illustrate disparities in spatial distribution of water resources, the Upper Awash sub-basin, which shares a water-divide with the CRVL sub-basin, has large flow volumes in the rainy season and suffers with seasonal flooding
This paper develops a conceptual Water Evaluation and Planning (WEAP) model to represent the main water supply and demand features of the sub-basins to estimate the optimal seasonal surplus water from the Upper Awash sub-basin that can potentially be transferred
Summary
The Central Rift valley Lakes (CRVL), have been faced with changes like water level reduction, land degradation, and overutilization [1]. The Upper Awash sub-basin, which shares a water-divide with the CRVL sub-basin, has large flow volumes in the rainy season and suffers with seasonal flooding. It lacks significant a storage facility to store the high seasonal water within the basin itself, since Koka Reservoir, which was constructed in 1960 was the only reservoir located in the sub-basin. Due to its long service year and sedimentation load, Koka Reservoir has lost about 40% of its installed storage capacity and currently stores only about 1 billion cubic meters (bcm), which is much lower than the annual surface water production of the Upper Awash sub-basin [11]
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