In West Africa, the resistance of dams to flooding

The torrential rains that have been falling for several weeks on the Sahelian strip and part of Central Africa are putting aging and often poorly maintained dams to the test. In northeastern Nigeria, the rupture of the Alau dam on Thursday, September 12, submerged a large part of the city of Maiduguri, located about twenty kilometers to the south. More than 400,000 people have been displaced, thousands of homes and essential health and education infrastructure have been destroyed.

After turning a deaf ear to previous warnings, the federal government announced this week the creation of a commission to assess the condition of all dams across the country. It will also have to make a complete diagnosis of Alau before its reconstruction.

In late August, the collapse of the Arbaat dam in Sudan affected 50,000 people and destroyed – in part or in full – twenty villages, in a humanitarian context already marked by a year of civil war. The city of Port Sudan has been deprived of its main fresh water reservoir. These two events echo the tragedy that occurred a year ago in Derna in Libya, devastated by a flash flood caused by the rupture of two structures under the weight of a record quantity of water brought by storm Daniel. Some 6,000 people died and several thousand are still missing, according to the United Nations.

Human and financial resources are often lacking

Should we see these as warning signs of other accidents to come? “In general, the risks of a dam breaking are minimal because safety standards include the probability of exceptional floods, but on the African continent, many structures are more than fifty years old. They are old infrastructures calibrated to a climate that has changed with more frequent episodes of abundant and violent rains. Very often, the climatic and hydrological assumptions on which they were designed are not known. Nor are their plans – particularly in regions in conflict for security reasons. This adds a lot of uncertainty and reduces the possibilities of anticipating disasters. In many cases, the spillways with which dams are equipped to manage excess water and prevent overflows will not be able to cope.”observes Micha Werner, professor at the IHE institute in Delft (Netherlands) and specialist in flood management.

While situations vary from one country to another, the researcher notes that human and financial resources are often lacking to ensure the proper functioning of these old infrastructures, whose role is to regulate the flow of watercourses and cushion the risks of flooding: “Flood and low water surveys are not carried out on a regular basis and we have less local data than we did fifteen years ago. However, they are the only ones that can provide us with a good understanding of the risks.”

In extreme cases, the future is simply left to the unknown, as in Sudan, where the Jebel Aulia dam is no longer being monitored. Located 40 km from Khartoum, in an area held by the rebels of the Rapid Support Forces (RSF), it has been deserted by its employees.

An “urgent” need for rehabilitation

The topic is also a challenge for the supply of electricity on the continent. In 2019, the International Hydropower Association published a guide for adaptation to climate change. Among its recommendations is the consideration of long-term climate scenarios produced by climate scientists. While the guide is not exclusively aimed at Africa, the measures it proposes have been tested before being approved on several dam projects, including the Mpatamanga dam in Malawi.

The African Development Bank (AfDB) has also addressed the issue as part of its programme to modernise the continent’s hydroelectric power plants adopted in June 2023. This project targets 87 units built more than thirty years ago. Twenty-one of them, representing more than 10% of the continent’s hydroelectric production, are in need ” urgent “ of rehabilitation. “The effects of climate change require additional adaptation measures”the financial institution emphasizes, citing the strengthening of flood protection, the improvement of early warning systems and the structural improvement of reservoirs.

While worsening droughts appear to pose a real danger to the energy supply of certain countries – as several southern African countries have been experiencing for months – episodes of extreme rainfall are also causing just as much concern for existing infrastructure. “It is always possible to make a structure more secure. But these are expensive jobs that are not always within the reach of countries.”notes Yves Giraud, former director of EDF Hydro.

This reality has not escaped Ghana. In 2022, the country was one of the first to put its infrastructure on the climate change test bench in order to develop its adaptation roadmap. The exercise revealed that five of its thirty-four dams were threatened, including the Weija dam, which provides 80% of the drinking water supply to the capital Accra. Their rehabilitation costs hundreds of millions of dollars. A cost that illustrates how much climate change is already weighing on the development of poorer countries like Ghana, as the Minister of the Environment, Kwaku Afriyie, did not fail to point out when presenting his plan to international donors.