Transboundary reservoir cascade system

In the neighboring Atbara basin, the construction of the Tekeze Dam in Ethiopia reduced flooding at Sudan's Khashm el-Girba Dam. This is because its much better to have larger impoundment of water in the deep gorges as in case of Tekeze in the northern Ethiopian Highlands. Similar effect can be achieved with the GERD. Like Atbara, the Blue Nile is also a highly seasonal river. The upstream GERD would reduce seasonal flooding of the plains surrounding the reservoirs downstream, especially the dam next door - the Roseires Dam.

The effect is doubled as during the drought years, GERD would act as buffer to shortages in Sudan and Egypt. Also, as in case of any reservoir cascade system, the upstream GERD would retain silt and increase the useful lifetime of dams in Sudan (Roseires, Sennar, Merowe) and Egypt (Aswan High Dam).

However, management of such large impoundment requires close coordination and cooperation between the Nile countries, mainly Ethiopia-Sudan-Egypt. The volume of the GERD (74 bcm) is about 1.5 times the average annual flow (49 bcm) of the Blue Nile at the Sudanese-Egypt border. This loss to downstream countries could be minimized by spreading over several years, fixing suitable water elevations at downstream reservoirs during the GERD filling period and reliable hydro-meteorological seasonal forecasts.

As with any big reservoir, evaporation would be another issue with GERD. However, the extent of evaporation in highlands of Ethiopia would be comparatively lesser than from the reservoirs in the Saharan deserts downstream.

With mHM augmented with new reservoir module, we aim at providing reliable lake-hydrological simulations and thus seasonal forecasting of hydro-meteorological indices six months into the future. Such a tool would facilitate in transboundary decision making between the Nile countries and in the process foster cooperation.