Extensive flooding could have severe consequences for farming, health and the environment.
By Miryam Naddaf – Nature Journal
The 66-year-old Kakhovka dam on the Dnieper River in south Ukraine collapsed on the morning of 6 June after a suspected explosion, triggering a catastrophic humanitarian and environmental crisis.
Spanning an area of more than 2,000 square kilometres, the dam’s reservoir is the country’s largest in terms of water volume. The dam has been controlled by Russian forces for more than a year.
The breach triggered extensive flooding, which peaked at a depth of 5.6 metres in Kherson on 8 June and has already displaced more than 20,000 people across dozens of settlements, including in Russian-held areas on the river’s lower-left bank. The deluge is expected to continue for at least a week.
Nature spoke to researchers about the continuing impacts of the disaster.
What are some of the immediate consequences?
Before the breach, the Kakhovka reservoir held more than 19 cubic kilometres of water. “Now, there are only 11 cubic kilometres of water left,” said Oleksandr Krasnolutskyi, Ukraine’s deputy minister of environmental protection and natural resources, in Kyiv, at a press briefing on 8 June.
The reservoir provides water for more than 700,000 people in south Ukraine. Cities on the Dnieper River, including Kherson, Nikopol, Marhanets and Pokrov, are short of water supplies, according to the United Nations.
And the flood waters themselves have caused extensive damage — destroying homes, roads and other crucial infrastructure.
How might the flooding affect farming and food security?
As the water level continues to drop, there will not be enough water for the irrigation canals that the reservoir usually serves, says Roger Falconer, a water engineer at Cardiff Univer- sity, UK, who models dam failures. “It could affect crops both downstream and upstream.”
Flood water has inundated large areas of farms and arable lands, washing away their topsoil layers, according to Ukraine’s environment ministry.
“We will not be able to cultivate agricultural plants on this soil for many years,” said Krasnolutskyi. Falconer adds that the floods could wash fertilizers used on agricultural land into the river, where they could disrupt aquatic ecosystems.
What are the other environmental impacts?
The sudden surge of water downstream has had immediate and far-reaching impacts on the bio- diverse ecosystems. “Nearly 160,000 animals and 20,000 birds are under threat because of the catastrophe,” said Krasnolutskyi.
Some of those species are rare, or found only in this area. They include the vulnerable Nord- mann’s birch mouse (Sicista loriger) and the endangered sand mole rat (Spalax arenarius), according to a report by the Ukrainian Nature Conservation Group (UNCG) in Vasylkiv.
The Kakhovka reservoir itself is home to dozens of fish species. The rapid draining of its water means that vast numbers of fishes will be either stranded in shallow, dried-up zones or swept away to sea, where they will perish in the salt water.
“What we have seen is the tip of the iceberg,” says Oleksii Vasyliuk, an environmentalist and co-founder of the UNCG. “This is ecocide.”
Nearby national parks have also been flooded, which will cause irreparable damage to their flora and fauna.
Nine sites in Ukraine’s Emerald Network, a Europe-wide conserved area, as well as five internationally important wetlands have been flooded. Around 55,000 hectares of forest have been inundated with water that is predicted to remain stagnant for 20 days, according to the environment ministry.
Does the dam’s proximity to a nuclear power plant pose a danger?
Europe’s largest nuclear power plant, in Zaporizhzhia, is located around 150 kilometres upstream of the Kakhovka dam. The plant’s six reactors have been shut down for more than eight months — but it needs cooling water to manage the residual decay heat. The reactor is continuing to pump cooling water in from the reservoir, according to the International Atomic Energy Agency.
If the water level in the Kakhovka reservoir drops too low to be able to supply cooling water, Zaporizhzhia can switch to alternative water supplies. There are also two cooling towers that use the atmosphere for cooling, and require only a small amount of water to operate, says Malte Jansen, an energy scientist at the University of Sussex in Brighton, UK.
Perhaps more concerning is the potential dispersal of toxic compounds. More than 150 tonnes of machine oil from the Kakhovka hydroelectric power station, which sits on the dam, have spilt into the Dnieper River, according to the environment ministry. The flood water also carried garbage, together with construction waste and sewage, into the Dnieper watershed, according to Krasnolutskyi, where it could potentially contaminate supplies of drinking water.
What can be done to address the situation?
If the reservoir’s water level continues to fall, it will eventually return to the baseline level before the dam was built, says Falconer.
He adds that the collapse will ultimately change the reservoir’s bed topography, and that it could also increase shear stress, the force of water flowing against the river bed, which would disturb any toxic sediment there.
“It will be necessary to either plant [upstream] areas with a forest, or sow meadow grasses so that the wind does not blow away this silt at the bottom of the dried reservoir, because it is contaminated with waste from Zaporizhzhia,” says Vasyliuk.
The environment ministry says that a scientific survey will be needed to explore whether the dam should be rebuilt. But a complete assessment of the flood’s impact is unlikely at present: Russian forces currently control the south side of the river, where most of the flooding has occurred.
“Nothing can be done to minimize the consequences,” says Vasyliuk. “This is a zone of both an environmental disaster and active hostilities.”
