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The cascade effect
Sharing information, knowledge and experience

Dominik Lehnert and Leila Bendra-Lehnert
The interdependency of dams in a river system demands coordination, so all dams have an optimal configuration that, in the interplay with all others, minimises risks and maximises benefits for all riparian states.
22.02.2021  |  Berlin, Germany
Sudan’s Roseires Dam. (photo: OFID / F. Albassam)
Sudan’s Roseires Dam. (photo: OFID / F. Albassam)

[This article is based on a presentation held by Michael Abebe in February 2020.]


The flow of the Nile differs depending on the seasons. Any particular area along the Nile banks might get too much water, leading to floods, or too little, causing droughts. This fluctuation between excess and deficit is typical, with irregular periods of balance in between.

The term ‘cascade dams’ refers to two or more water storage dams situated along the same river or in the same river basin. These dams are coupled such that the operation of one reservoir affects the function of the others. Depending on how harmonised these operations are, the overall impact can be either positive or negative.

All dams must follow some fundamental principles.

If the operators of each dam are aware of the others' needs, and if all operators agree to work cooperatively, the overall negative impact would decrease.

For a coordinated operation of cascade dams to succeed, all dams must follow some fundamental principles. These include the need to access and share accurate data, particularly relating to weather and hydrology forecasting. Each dam must operate with a view on maximising overall benefits for the entire river basin. Sharing these increased benefits between and within countries, as equitably as possible, is a must.

Additionally, it is vital to set up operating procedures and the necessary legal and institutional frameworks. Both the procedures and the frameworks must also include a degree of reasonable flexibility to allow future operators to deal with unexpected and unforeseen situations.

Finally, all stakeholders representing various sectors affected by the operation of cascade dams must be consulted regularly, and their views and concerns must be addressed.

The case of the Blue Nile

Along the Blue Nile river, there are five particular dams of interest to look at: The High Aswan Dam in Egypt, the Merowe, Sennar and Roseires dams in Sudan and the Grand Ethiopian Renaissance Dam in Ethiopia.

Dams are used for diverse reasons such as to produce hydropower, to supply water for consumption and irrigation, to mitigate floods, but also for navigation, fisheries and recreation.

Conflict may arise when the operation of one dam adversely impacts the purposes of another. For example, to generate hydropower, one dam might keep most of the water coming in, therefore filling its reservoir. Less water will then be available for subsequent dams on the river.

It is important to note that the Nile’s water is not evenly distributed amongst Nile Basin countries, which leads to an equally unevenly distributed potential to develop water resources. According to the Nile Basin Initiative (NBI), the projected water demand in the 20 years from 2014 to 2034 will increase by 60 percent in the Nile Basin.

The cooperative operation of dams could bring many opportunities.

Balancing needs and interests means that each party's needs must be acknowledged as legitimate and served in a sustainable, equitable and efficient manner.

So what is stopping the Nile Basin countries from enacting such cooperation agreements based on balancing needs?

The cooperative operation of dams could bring many opportunities, such as helping to adapt to climate change by bridging droughts and preventing flood damage, in addition to providing hydropower for the whole of the Eastern Nile region.

It is critical to capitalise on the hydrological knowledge already existing and take advantage of the enabling environment created through the continuous cooperation between the Nile Basin Initiative and its Eastern Nile Technical Regional Office (ENTRO).

This could help encourage countries to jointly set up data exchange and consultation mechanisms and common standard guidelines and rules for dam operation. Bringing together all the Eastern Nile region actors in a concerted effort to bridge weaknesses and fortify strengths would help build a future of increased prosperity and harmony.

Levels of cooperation

To support countries in building this future, NBI/ENTRO is involved in several projects related to improving forecasting and improving dam safety, for example. Maybe most urgent of all, NBI/ENTRO is currently developing a roadmap containing different options for coordinated operation of the existing and planned dams.

Concretely, different levels of cooperation are possible concerning a coordinated dam cascade management in the Eastern Nile.

The first level is data exchange amongst different stakeholders. Cooperation is based on a local perspective, which translates into minimal changes to already established operations. Still, it leaves the door open for the possibility to adjust operation, depending on the data received from other dams.

The second level of cooperation includes the local perspective and a system perspective. The local operation rules are in place but are subject to adjustments, making it possible to share benefits if agreements on joint objectives are developed.

The total benefits for both Sudan and Ethiopia were higher than the baseline.

Full cooperation comes at the third and last level. It is based on a system perspective where the assessment of operation rules follows joint objectives across borders. Different organisational structures for regulation, management and operation can also be set up.

To exemplify these levels of cooperation in real life, ENTRO ran several models on the Atbara-Tekeze sub-system, which consists of three dams: the Tekeze Dam, located upstream in Ethiopia, operated to meet hydropower requirements; the Upper Atbara Dam, located downstream of Tekeze at the confluence of Setit and Atbara River; and Khashm el-Girba Dam, downstream of Upper Atbara, operated to supply the New Halfa irrigation scheme.

Whichever level of cooperation the model relied on, the total benefits for both Sudan and Ethiopia were higher than the baseline. Following the current mode of non-cooperation operation of dams deprives both countries of a multitude of benefits – just in monetary terms worth millions of dollars.

This modelling was a successful way to describe and demonstrate the different levels of cooperation and coordination of cascade dam management. Therefore, looking at the whole of the Eastern Nile as an interconnected system is an essential step on the road towards full cooperation.

This article is part of:
A boat cannot go forward if each rows his own way


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