Situation Analysis summary: Hydrology

A summary of the hydrology in the Omo-Turkana Basin, from the situation analysis.

Alexa Marsh

The Gibe III dam and commercial plantations will affect both the quality and quantity of water available to down-stream regions. Lake Turkana will be directly affected by the operation of the Gibe III and Gibe IV dams because the Omo river (on which the Gibe III is already built) provides Lake Turkana with over 80% of its inflow. The dam has permanently dampened seasonal flow variability in the Omo River, eliminating the annual flood pulse (to learn more about how the dam works, see our blog on “The Gibe III”). Assessing the impact of Gibe III has been complicated by the lack of flow data for the Omo River, last measured by the Ethiopian Water Resources Authority in 1980. Hence, hydrological studies of the Basin have made use of satellite datasets to model the water balance. Before the construction of the dam, the Omo had a naturally fluctuating flow rate and flooded annually between July and October. The filling of the Gibe III reservoir caused a decline in Lake Turkana water levels of 1.5 m between January 2015 and January 2017 and thereafter regulated downstream river flows. Further reductions in lake levels are expected due to irrigation abstractions, with the magnitude of decline depending on the final extent and management of the new plantations. A worst-case scenario would be the complete drying of Lake Turkana, prompting analogies with the Aral Sea and Lake Chad environmental disasters.

As a result of declining lake levels, the shoreline of Ferguson’s Gulf, an important area for fishing and fish breeding, and the only sheltered area on the western side of the lake, has receded significantly, and the mouth of the Gulf has narrowed to less than 1 km. Further declines in lake levels due to irrigation abstractions would result in a complete drying of Ferguson’s Gulf, leading to a loss of fishing livelihoods for surrounding communities and exacerbating food insecurity in the region.

For further information, see the recently published paper “Lake Turkana, major Omo River developments, associated hydrological cycle change and consequent lake physical and ecological change” by Drs. Sean Avery and Emma Tebbs.

Sean Avery achieved his BSc and PhD in civil engineering at the University of Newcastle-upon-Tyne, specializing in hydrology and hydraulic structures. He is an independent consultant in Kenya, affiliated with King’s College London, and listed in the Kenya Gazette to practice in water supply, irrigation, effluent treatment and dams. Dr. Avery wrote a seminal article, “What Future for Lake Turkana?”, on the impact of hydropower and irrigation on the world’s largest desert lake.

Dr. Emma Tebbs is a Lecturer in Physical Geography and Remote Sensing at King’s College London. Her research focuses on the remote sensing of aquatic and terrestrial ecosystems.

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