Impact of water abstraction on water balance of Lake Ziway, Ethiopia

Abstract

The available water volume of Lake Ziway in Ethiopia is declining at an alarming rate which hinders the lake services for a wide variety of sectors. However, there is a lack of systematic study to evaluate the contribution of water withdrawal by various sectors to the decline in the lake actual storage. In this study, we conducted a Water Abstraction Survey (WAS) to estimate actual water withdrawal from the lake. We applied a water balance model to evaluate the isolated impact of water withdrawal on the lake water volume and level. Three development pathways were simulated and the likely impact of these pathways on the lake water volume and level were assessed. Results indicate that water withdrawal for irrigation and domestic has significantly contributed to the change in the actual storage of Lake Ziway. Under full development pathways, irrigation water withdrawal from the lake is estimated to be 95.3 MCM. This will cause the mean annual water level of the lake to drop by 0.94 m, which yield with 38 km 2 reduction of the surface area of the lake. Overall, this will result in a reduction of mean annual lake volume by 405 MCM, which accounts for 26% of the average lake volume. Hence, our result indicates that the current impact of water abstraction on Lake Ziway storage is substantially large and will exacerbate in the future. This calls serious action on the management of water abstraction from the lake.