Alem Gebriel, PhD, PE
Water Resources Technical Director
For several years now, Ethiopia, Egypt, and Sudan have been negotiating the filling and annual operations of the Grand Ethiopian Renaissance Dam (GERD). The negotiations among the three counties have been very difficult, mainly because of Egypt’s position to maintain the status quo. Broadly, the main sticking point appears to revolve around Egypt’s insistence on maintaining the 1959 water share agreement, which divides the Nile water between Egypt and Sudan, allocating a zero share for other riparian countries including Ethiopia. In fact, Ethiopia and other Nile riparian countries were not party to the 1959 agreement. Ethiopia noted its opposition at the time when the agreement was drafted. Except, for the Declaration of Principle (DoP) signed in Khartoum, Sudan, in 2015 by the heads of state of the three countries; any others agreement has not been signed, yet. Reportedly, agreements have been reached on most of the key elements on the staged filling of the Dam, but a final agreement remains elusive. According to news outlets, a critical bottleneck is the demand initially by Egypt and now also Sudan for a so-called legally binding agreement, which Ethiopia interpreted as a water-sharing agreement intended to foreclose any future developments upstream of the GERD. A water-sharing agreement requires participations all the Nile basin riparian countries and would include matters unrelated to GERD.
In recent months, Sudanese Officials have been making statements that are not supported by facts. The foreign minister reportedly stated that GERD endangers the lives of 20 million Sudanese people, and the Minster of Irrigation and Water wants to sue Ethiopia and the dam Contractor Salini Impregilo. It is beyond comprehension that these officials disregard the benefits of GERD to the Sudanese people in eliminating flooding and modulating flow fluctuations for a steady supply of water for domestic use and irrigated agriculture. GERD is perhaps the only major project known so far that may rid Sudan of its centuries-old flooding problems (https://borkena.com/2021/04/24/renaissance-dam-gerd-salivation-to-flooding-in-sudan/
Filling of GERD is an integral part of the construction of the dam and is planned to take place in several stages spanning many years. It is projected that filling up the reservoir to elevation 640 m will take approximately 7 years. Ethiopia has completed the first stage of filling on July 21, 2020, with 4.9 billion cubic meters (BCM) of storage. During this first stage of filling, over 90 million cubic meter (MCM) per day, or over 1,042 cubic meters per second (cms), was released in mid-July 2020 through the diversion outlets until the reservoir overtopped the center block of the dam that stood at a 560 m elevation. These figures from the Ethiopian Minister of Water, Irrigation and Energy are corroborated by the 2020 stream gage record at El Diem station. The release in the month of July 2020, was four times the average drier month flow of the Nile river measured at El Diem stream gage location. Despite this release, the Sudanese Minister of Water and Irrigation, Yasser Abbas, stated that water supplies in Khartoum and other locations were disrupted because of the GERD filling. One wonders about the cause of such disruption when the flow was four-times the average drier month flow in the river. There is another reason for why the filling of the GERD cannot be the cause of the alleged disruption of water supply in Sudan: there are two reservoirs downstream of the GERD in Sudan, called Rosaries and Sennar, that control the water flow before it reached Khartoum. Thus, if the statement by the Minister of water and Irrigation is true, Sudan needs to examine the operation of its water supply systems and take corrective actions accordingly instead of making the GERD a scapegoat of the ostensible disruption.
The second filling of the GERD is planned according to the agreed schedule in the upcoming rainy season, namely from July to September 2021. In preparation for the second filling, it is reported that Ethiopia has released more than one BCM of water in April 2021, to lower the water surface elevation in the reservoir below the 560 m center block elevation of the dam. The plan, according to Ethiopian Officials, is to increase the center block elevation to 595 m to impound additional 13.5 BCM of water, which raises the storage in the reservoir to 18.4 BCM. Turbine testing and early power generation is planned for August or early September 2021. It is important to note that, during testing of the turbines and early power generation, additional flow will be released from the dam. It is very likely that the annual volume released from July 2021 through June 2022 (water year), could exceed the average annual flow of the Nile, which is 49 BCM.
Figure, 1 shows the level of Lake Naser at Aswan dam from altimeter measures taken from and Jason-1 and Jason-3. The April 04, 2021 elevation is at 178.77 m. Aswan is full to the brim and the capacity is estimated over 2 years’ worth of supply.
A reservoir operation scenario analysis was carried to demonstrate the duration of filling. To get a better understanding of the second filling duration and downstream release amounts, a reservoir simulation exercise was performed using HEC-ResSim. HEC-ResSim is USA Army Corps of Engineers software package that has been in existence since the 1960’s in various versions and is well-tested and widely used. The input parameters for the simulation at a minimum are physical parameters of the reservoir such as storage, outlet release capacity, inflow to the reservoir, and downstream release amounts. The initial GERD reservoir was set at elevation 557 m and the center block elevation of the dam was set at 595 m. A drier month release of 300 cms was assumed for environmental flows.
The year 2021 is forecasted from various organizations as above average wet year. For these exercise, four reservoir inflow scenarios were assumed: a very wet year, wet year, average, and below average year inflow, Figure 2 (b). The flow values were indexed from the historical records to develop input data to represent the four scenarios using the El Diem (located close to Ethiopia and Sudan border) stream gauging location. Two downstream release scenarios, 1,000 cms, and 2,000 cms, in July through August or until overtopping commences were tested. The downstream releases are selected neither to cause significant disruption for downstream operation nor to trigger flooding. The release amounts are hypothetical scenarios and should not be taken as a policy of the Ethiopian government. Only the 1,000 cms results are presented in this article, Figure 2 (c). The results for 2,000 cms releases would extend the filling period by a few weeks for the respective inflow inputs to the reservoir. Once the filling is achieved to elevation 595 m after August or end of September, more release would occur through the center block of the dam. The results for the four scenario analyses are summarized in Table 1 and Figures 2 and 3. In all cases, GERD reached the target elevation of 595 m before end of September, Figure 2 (a) and 3. After overtopping elevation 595 m, the peak flow would be as high as 6,000 cms and as low as 2,000 cms, Figure 2 (c), for the very wet and below average year scenarios, respectively. The flow for the other two scenarios is between 6,000 cms and 2,000 cms.
While the facts are as discussed in this article, the claim that GERD would disrupt downstream operations is unfounded. Also, Egypt would not die of thirst because Aswan is full to the brim and there would be adequate amount of flow for downstream release from GERD. It is estimated that during the months of June through Decembers, 27 to 45 BCM would be released through the bottom outlets excluding releases from the planned turbine testing and early power generation for the scenarios analyzed. In cases of an unfortunate situation, where for example forecasts fail or an unusual drought occurs, it is reported that the Ethiopian government has expressed desire to postpone the second filling in the spirit of brotherhood and sisterhood with the Sudanese and Egyptian people, and to enhance cooperation in the region in general. Therefore, the current controversy has little to do with GERD impacts; it is a struggle between holding onto the past and looking toward a new paradigm to right the wrong.
Alem Gebriel is a water resources Technical Director with a global engineering company. He has over 30 years of experience in water resources planning, hydrology, hydraulics, and feasibility studies for flood mitigations and, simulation of reservoir operation.
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