Dams are important to conserve water for sustainable development, prevent flood damage, and store water in seasons of plenty to use in seasons of drought. Today, over 900,000 dams are estimated to exist worldwide, 40,000 of which are on a scale large enough to be considered as mega-dams. Although there is no universal definition of what qualifies as a mega-dam, as a general rule they are large structures over 15 metres in height and generating on average over 400 Megawatts of power. Mega-dams in upstream river countries are not recommended under the 1997 UN Convention on the Law of Non-Navigational Uses of International Watercourses because they infringe on the right to water and the accepted rights of downstream countries. They cause extreme impacts on the downstream environment and biodiversity, in addition to on the river course itself. Such dams in upstream river countries require complete studies to be undertaken before their construction showing their impact on the river hydrology and the environment as well as their socio-economic impacts on downstream countries. Upstream countries should guarantee a minimum level of water discharge to avoid any significant hazards to the downstream countries. The Grand Ethiopian Renaissance Dam (GERD), which is being built as a result of a unilateral Ethiopian decision without advance agreement from Egypt and Sudan, will cause severe impacts on the course of the River Nile and harm the environment and agriculture in both downstream countries. Constructing mega-dams in upstream countries is a completely different story from constructing them in downstream countries where no harm or negative impacts are caused. In fact, by constructing mega-dams, downstream countries are saving water from going to waste in the sea, and they do not cause damage to second or third parties. In contrast, upstream mega-dams always cause extreme environmental, hydrological, and socio-economic impacts. For example, the GERD, with a height of 145 metres, a length of approximately 1,800 metres, and a saddle dam supporting the main dam that is 50 metres in height and 4,800 metres in length, will create a reservoir with a capacity of 75 billion cubic metres (BCM) of water. If surface evaporation and deep seepage are taken into account, that makes a total reservoir of 90 BCM. After the building of the GERD, Egypt, a country already suffering from food insecurity, will have to import 75 per cent of its essential crops, a 10 per cent increase on what it currently imports. This will mean a higher food-import bill of $18 billion, compared to the current $13 billion. Land in both the Delta and the Nile Valley will suffer immensely from increasing salinity and the intensive use of chemical fertilisers that will be necessary to increase production after the expected water shortages because of the GERD. The reduction in the amount of water reaching Egypt will lead to a decline in the extent of its agricultural land and a loss of almost two million acres, with the increasing vulnerability of the Nile Delta to climate change and sea-level rise and seawater intrusion. Native flora and riverine weeds, fauna, forests, animal habitats, amphibian species, and wildlife will also be affected by this mega-dam. Another impact is the effect of the GERD on climate change. Greenhouse gas emissions will increase from the GERD's reservoir due to the decomposition of organic matter and plant residues that enter it as a result of the silting processes of the Blue Nile. This will cause high carbon dioxide emissions and a severe drop in the soluble oxygen consumed by microorganisms, leading to the death of fish in the river stream for years to come. The GERD will decrease the water that arrives in Egypt by 10 to 12 BCM per year, which will mean that more than five million people will lose their jobs in the agriculture and fishing sectors. Evaporation from the Nile course will increase because the water flowing to Sudan and Egypt will be shallow. Of course, Ethiopia should guarantee acceptable amounts of water to the downstream countries to minimise the significant negative impacts of its mega-dam. The GERD being constructed on the Ethiopian border with Sudan at a distance of between five and 20km because it is curved in shape will hit Sudan especially hard and notably the Blue River and Sennar states in eastern Sudan. The GERD will also prevent 86 per cent of the sedimentation of the Blue Nile, amounting to 136.5 million tons of silt. The loss of these fertile silt and clay particles will clearly affect the fertility of Blue Nile state agricultural land in Sudan. The absence of such alluvial sedimentation will mean that more nitrogen and phosphorous fertilisers will need to be added to the soil. This will lead to a decrease in food safety criteria and will increase the contamination of shallow ground water by nitrates, especially in the rainy areas of eastern Sudan. Moreover, the expected heavier use of phosphorus and potassium fertilisers will also increase soil contamination, especially with cadmium and other heavy metals, as well as increasing chemical fertiliser residues in all food products from this area. The pattern of agriculture in the Blue Nile states in Sudan will change from basin agriculture, which relies mostly on flood water that is stored in the soil and at root-zone depth, to permanently irrigated agriculture, which means the increased use of chemical fertilisers and chemical pesticides. The use of such pesticides in irrigated agriculture after the completion of the GERD will increase the probability of cases of cancer in eastern Sudan. Meanwhile, irrigated agriculture without the construction of good drainage systems will cause waterlogging, or the saturation of the soil with water, and shallow ground water. Sudan, with its weak financial resources, will not be able to construct a complete drainage system for its new pattern of irrigated agriculture, and it is likely to postpone doing so until the water table rises and becomes a serious problem. Such waterlogging and poor drainage will hit all the agricultural land of the Blue Nile and Sennar states in Sudan. Increasing soil salinity will be the main problem in the eastern Sudan over the next 30 years, as happened in Egypt after the building of the Aswan Dam prevented the Nile's flooding from leaching agriculture land of salt accumulation. The GERD will turn the River Nile almost into an irrigation canal due to the controlled daily water discharge delivered from the mega-dam according to the power generation needed. This will cause severe changes to the river stream, and bank erosion will undoubtedly happen, especially on the Blue Nile in eastern Sudan. The writer is a professor of Soil and Water Sciences at the Faculty of Agriculture at Cairo University. *A version of this article appears in print in the 25 June, 2020 edition of Al-Ahram Weekly
