Flood protection engineers face new challenges as the climate changes.
The devastating flood in Venice this November has given rise to talks about the risk of floods in St. Petersburg. The city seems to be well protected by the dam, but what if it will be unable to contain the surging water? Yevgeny Solovyov, Channel Saint-Petersburg reporter, has asked specialists to comment.
195 years ago, in November 1824, St. Petersburg faced the most devastating flood in its history. The Neva River surged 4 meters and 21 centimeter above its normal level flooding the streets and destroying the buildings and bridges of the city. The cataclysm was described by Alexander Pushkin in his poem “The Bronze Horseman”. That flood killed 480 people, according to the official statistics. Historians insist, the actual death toll was 10 times higher.
The flood of 1824 resulted from a so-called long wave generated in the Atlantic and driven by strong westerly winds. A hundred years later, in 1924, the wave was back bringing another heavy flood. No surprise that St. Petersburg is expecting the soon-to-come 2024 with anxiety. And specialists believe there are grounds for concerns.
Yury Shevchuk, an ecologist, reminds about one more tragic consequence of the flood in 1724 – it was in the flood that Peter the Great caught a cold and died. The centennial flood cycle is not something to be dismissed, he believes.
St. Petersburg has been protected from the floods from the sea side for eight years already. The 25.5-kilometer dam is unique hydraulic structure combining ingenious technical solutions. Its giant mechanisms move and close heavyweight locks automatically within several hours if there is a slightest threat of flooding.
Since 2011 when the dam was put into operation, St. Petersburg could have been flooded 18 times, but every time the locks were closed.
The need to build a dam to protect St. Petersburg was recognized in the 1970-s. The construction started in 1979, and all the technical decisions were developed in that period, in the Soviet era, by Soviet engineers, under the planned economy.
‘All the calculations were based on the climatic conditions at that time. Now the climatic situation is changing, the climate is deteriorating, cyclonic activity is increasing. But the dam has a good safety margin’, says Igor Polischuk, Deputy Director of the Saint-Petersburg Flood Prevention Facility Complex (that is the official name of the dam).
The dam will withstand even a sea wave 5.5 meters high. The mathematic calculation was precise. But the changing climate poses challenges that call for future engineering solutions.
Valery Tsepelev, Head of the Northwestern Hydrometeorology and Environment Monitoring Directorate, warns: ‘Nowadays, floods, unlike those in the past, can last for a long time. Two and even three waves can come, this already happened in the past years. And while the dam remains closed for a long time, the Neva estuary is getting filled with water coming not from the Gulf of Finland, but from the river’.
The Neva brings some 2,600 cubic meters of water a minute to the estuary. Should it be locked, the river will fill the estuary basin within 48 hours. And after that, there will be a catastrophe. This makes specialists get back to the idea of building one more lock system in Shlisselburg that will cut off, if necessary, water transit from Lake Ladoga.
And one more thing to consider is, we need to stop building new artificial territories that are reducing hectare by hectare the Gulf basin and thus disrupting the fragile balance and posing a risk of natural disaster.
Photo: St. Petersburg TV channel