Hydrological Impacts of the Grand Ethiopian Renaissance Dam (GERD) on River Nile Hydrology Within Sudan

Abstract

This paper aims to quantify the potential impacts of the Grand Ethiopian Renaissance Dam (GERD) on the River Nile System within Sudan territories, in the context of hydrology. GERD reservoir with a capacity of (74 Km3) is approximately 1.5 times the mean annual flow of the Blue Nile, which contributes by 57% of the River Nile runoff. According to Ethiopian proposal, the GERD is going to be filled to the full supply level of 640 m a.m.s.l in 6 to 7 years. The first filling of GERD reservoir was planned to be in 2014, but it is postponed until the writing of this report. However, it's most likely to be started this year 2020. Consequently, significant impacts are highly anticipated during this first filling period, and all over the long-term operation. Definitely, this will change the Blue and Main Nile hydrological regime. In order to achieve the research objectives, a daily time step Rule Based Simulation model has been developed using River Ware Software (University of Colorado) representing the entire River Nile system within Sudan. Three scenarios were adopted, baseline (Hydrological System without GERD), GERD first filling and long-term operation. River inflows, water levels, run-off and hydrograph shapes within Sudan water system were investigated and compared to the average baselines, taking into consideration the recent Dams’ operation policies and rules. In addition, a simple-approach operation scenario was adopted for GERD. Likewise, as hydrological inputs, 30 years of historical time series were used. Given the above, the hydrological impacts in six representative River Nile reaches within Sudan were estimated, then highlighted and judiciously investigated. In summary, it could be concluded that, during the first filling of GERD, the runoff of the Blue Nile will decrease by 30%. While, for the Long Run, significant changes are expected for to the Blue Nile hydrograph, resulting in slight to moderate changes for the Main Nile Hydrograph. It’s expected that the impacts of GERD on River Nile hydrology will lead to increasing average discharges during summer period by a range of 10 - 500% for different months and hydrology, on the other hand, reducing flood peak by approximately 10-25%. In the long run, Water Levels in different reaches are expected to vary by ± (2 to 3) meters. It's concluded that operation policies of the existing Sudanese dams will no longer be valid for the new Situation after GERD, further studies are highly recommended to be conducted.