Lake Turkana will be directly affected by the operation of the Gibe III dam. This blog outlines the scope of these impacts.
Lake Turkana will be directly affected by the operation of the Gibe III dam. The Omo river that the dam is built on provides Lake Turkana with 80% of its inflow.
A study was done to model how the operation of the dam will affect the flow and water levels of the lake. Three approaches were used: a historical approach, a rainfall scenario based approach, and a statistical approach.
The historical approach used data from 1998-2009 of rainfalls to compare the characteristics of the lake with and without the dam present.
The scenario based approach used previous studies on the rain variability in the region to create three categories of yearly rainfalls: above normal, near normal, and below normal. These three categories were randomly assigned to the 12 years in 20 different scenarios and the same simulation as before was run.
The third approach was a statistical approach using nonparametric bootstrap resampling (NBR). This approach allowed possible future data to be included in the simulation. These values were applied and run again through the 12-year scenario.
The historical approach showed that the dam took 8 months before it was operational while the reservoir filled, and during that time, there was a 0.65m drop in the lake. The dam took anywhere from 8 to 16 months to fill with a depth loss range of 0.8 and 1.6m using the rainfall scenario approach. The statistical approach predicted the time to reach the minimum operating line would be between 5 and 15 months with a loss of 1.2m. In all scenarios, there was a significant difference based on the initial levels of the lake at the time of beginning to fill the dam.
According to the Economist, the had been filling for 18 months and the average depth of the lake had fallen by 1.5m during that time. The region also did not see its annual flood in 2015, while the flood in 2016 was too small to sustain crops.References
Velpuri, N. M., & Senay, G. B. (2012). Assessing the potential hydrological impact of the Gibe III Dam on Lake Turkana water level using multi-source satellite data. Hydrology & Earth System Sciences Discussions, 9(3), 2987-3027.
The Economist (2016). Ethiopia opens Africa’s tallest and most controversial dam. Available from: https://www.economist.com/news/21712281-gibe-iii-dam-has-capacity-double-countrys-electricity-output