The power of water: St. Petersburg is threatened by an abnormal July flood

The water level at the dam in St. Petersburg rose above 180 cm on July 4. This is considered an abnormal phenomenon for July, as the last time a cyclone of similar strength covered the Northern Capital was 160 years ago. About what could have caused the July floods in the 21st century and how many floods there were in the city, see the Izvestia article.

When and at what time is the historic flood expected in St. Petersburg

Forecasters predicted a historic flood for St. Petersburg in terms of weather on July 4. Meteorologists have dubbed it an anomaly for this time of year. The thing is that the last time such a disaster occurred in St. Petersburg in July was on July 12, 1865— exactly 160 years ago.

As of the morning, the water level at the dam in St. Petersburg rose above 180 cm, the Directorate of the city's Complex of Protective Structures (KZS) reported. It was closed the day before to prevent sea flooding.

"The flood would have actually already taken place if the gas station had not been closed. So it's safe to say that St. Petersburg experienced the second flood in the entire history of the city in July," said Alexander Kolesov, St. Petersburg's chief weather forecaster.

According to him, the water level in the Neva River rose to 95 cm with the doors of the complex of protective structures closed. In the waters of the Gulf of Finland, westerly wind gusts were observed up to 22-27 m/s. In St. Petersburg, from 15 to 19 m/s, in the waters of the Nevsky Bay in the area of Kronstadt and the Dam, the wind speed reached 20-23 m/s.

At the same time, due to strong winds in the city, the "yellow" weather danger level was extended - gusts can reach 20 meters per second, in coastal areas — up to 24, local authorities said. Due to bad weather, the parks of the Peterhof Museum-Reserve, as well as the Summer and Mikhailovsky Gardens, were temporarily closed to visitors.

Why there will be flooding in St. Petersburg

Flooding in St. Petersburg was expected due to the cyclone's trajectory. The reason is that a cyclone passing over the city will provoke an increase in the strongest westerly wind, gusts of which will reach 20-25 m/s in the waters of the Gulf of Finland, which will create a surge of water towards St. Petersburg.

Specialists from the KZS Directorate began monitoring hydrological processes in the Baltic Sea and the Gulf of Finland more than 60 hours before the expected flooding. According to their forecasts, the storm surge in the Baltic Sea may exceed 200 cm. Experts indicated that the westerly wind would pick up on the morning of July 4 and persist for most of the day, weakening by the night of the 5th.

At the same time, according to Tatyana Pozdnyakova, a leading expert at Meteonosti, the cyclone that is forming over the Gulf of Finland will be short-lived, and the flood peak is expected on the night of July 5. She noted that the cyclone will bring a strong westerly wind with gusts up to 20-25 m/s, which will create a water backup and prevent the Neva River from freely discharging water into the bay.

It is noteworthy that after the maximum water rise on the night of July 5, the level may begin to decrease as the cyclone shifts to the east. Despite the use of protective structures (dams), a significant rise in water in the Neva River, canals and small rivers is still predicted in the city.

Pozdnyakova, in an interview with Izvestia, stressed that the weather situation this year resembles winter conditions, a traditional period for such elements. The flood event in July is truly unique and extremely rare.

What floods have happened in St. Petersburg?

In total, more than 300 floods have been recorded in the history of St. Petersburg. Floods were often caused by storm surges in the Gulf of Finland, which were caused by cyclones and strong winds that prevented the free discharge of water from the Neva River into the Gulf.

The first recorded flood after the founding of the city occurred in August 1703, when the water rose by more than 2.5 meters, flooding Hare Island. Further, the flood of 1777 occurred in the city with a rise in water to 3.21 meters, which caused serious damage to the city and led to the deaths of thousands of residents. As a result, after this event, granite embankments began to be built to protect them from water.

The most significant and devastating was the St. Petersburg flood of 1824. Then, on the night of November 7 (19), the water level in the Neva River rose by more than 4.2 meters above normal, which led to flooding of a significant part of the city, the destruction of hundreds of houses and the death of several thousand people.

The second largest flood (3.8 meters) occurred on September 23, 1924. The disaster flooded about 70 square kilometers of the city, there were deaths, and bridges and piers could not withstand the onslaught of nature.

In September 1975, Leningrad experienced one of the largest floods in the city's history, with water rising to 2.81 meters. A powerful cyclone caused strong westerly winds of up to 25-30 m/s, which caused water to surge from the Baltic Sea into the Neva River and flooding of coastal areas. Residential areas, industrial enterprises and infrastructure, including metro stations and ambulance services, were affected.

This event has become one of the main incentives for the construction of a protective dam, which has effectively prevented large-scale floods in St. Petersburg since 2011.