Floods

Рубрикатор / City Topography/Nature and Natural Phenomena
FLOODS. Raises of water over 160 centimetres above the zero-level of Kronstadt Tide-gauge or over 150 centimetres above the zero water level of the Neva River (the water post is located near the Mining Institute). Approximately 290 floods have been registered in the history of St. Petersburg. They are mainly caused by the occurrence of combers, especially those crossing the Baltic Sea from south-west to north-west. The formation of a comber wave is caused by a lowering of atmospheric pressure in the centre of the cyclone and by the winds blowing to the centre of the cyclone. Western winds blowing from the Gulf of Finland and form a pileup of water and seiches at the mouth of the Neva - fluctuations of the total mass of water in the gulf trying to balance out, having been piled up, also contribute to the formation of floods. The role of seiches in the formation of the Neva floods is especially great when cyclones move together with an interval of 24-28 hours. In winter, floods may be caused by ice jams - accumulations of bottom and beaten ice blocking the way for water coming from upriver. Floods in separate parts of the city are determined by the height of their location. The districts bordering upon Nevskaya Bay, the Bolshaya Neva and the canals of the western part of St. Petersburg are the first to be flooded. With an increase in water levels, the water flows towards the east, covering territory along the coast to the former coastline of the ancient Baltic Sea, which serves as a boundary of the flood zone during the severest floods. At the beginning of the 18th century flooding occurred when the water level rose 130-150 centimetres above the zero water level in the Neva at the beginning of the 18th century. Today flooding occurs when the water level reaches 170-180 centimetres above the zero mark. This is explained by the increasing height of the city as a result of digging canals, deepening rivers and the bottom of the Gulf of Finland, the construction of the embankments and paving and asphalting of the streets etc. The flooding of parks, gardens and thinly populated districts starts when the water level reaches 180-200 centimetres and residential areas start to flood when the water level reaches 200-210 centimetres above the zero mark. During catastrophic flooding an area exceeding 100 km2 is immersed. The speed with which the waters rise on the Neva, the duration of the high level and abatement of the flood are dependant on its intensity. With a flood of 150-200 centimetres, the water rises at a rate of 22.5 cm/h, it subsides at 15 cm/h. The most rapid flooding was registered on 15 September 1929 and 1 October 1994, with the waters of the Neva rising at a rate of 100 cm/h. The duration of a flood varies from eight hours to two-three days. On average it is about 24 hours. On average it takes about eight to nine hours for the water to reach its high level mark. As a rule, the average time for abatement is 1.1-1.5 times slower than that of the inundation. Flooding on the Neva may occur at any time. 138 floods out of 267 happened in October-November during the period 1703-1986. This is the result of increased cyclonic activity during this season. Isolated instances of floods have been registered during the February to July. The six most substantial floods should be noted. In August 1703, the water in the Neva rose 200 centimetres. The second important flood happened on 21 September, 1777 (310 centimetres above the zero water mark). It was one of the most sudden floods in the speed of rising and caused many victims. The whole territory of St. Petersburg was flooded, many buildings and constructions suffered damage. The Summer Garden was seriously damaged. The most catastrophic flood in the whole history of St. Petersburg occurred on 19 November 1824. Water rose 410 centimetres above the zero watermark, the whole city was flooded with the exception of Liteinaya Part, Rozhdestvenskaya Part and Karetnaya Part. According to the official data, 208 people perished, according to unofficial data, up to 14,000 people perished, 324 buildings were completely destroyed and 3,257 buildings were damaged. Only 12 vessels survived out of 97 vessels lying in the harbour. The total damage cost approximately 20 million roubles. This flood was immortalized by Alexander Pushkin in The Bronze Horseman, A. S. Griboedov and F. V. Bulgarin et. al. also wrote about it. Another catastrophic flood (369 centimetres above the zero water level) occurred on 23 September 1924, when 61% of the territory of the city was flooded, up to 600 people perished, 19 bridges were damaged. Here and there the depth of the floodwaters achieved 2-2.5 metres and the wind speed achieved 40-42 m/sec. The last two substantial floods occurred on 15 October 1955 (282 centimetres above the zero water mark) and on 29 September 1975 (270 centimetres above the zero water mark) but did not cause substantial damage. The high water mark of catastrophic floods is marked by commemorative plaques with 26 marks surviving from the flood of 1824 and 24 marks surviving from the flood of 1924. The maximum level of rising of water is also fixed at the opening of Nevsky Gates of St. Peter and Paul Fortress and on the granite obelisk installed in 1971 on the bank of the Moika River near Siny Bridge. In some years there is no major rising in the amount of water in the Neva. The maximum number of floods to have been registered in one year was ten, which happened in 1983. The last instance of flooding was registered in the early 1990s, the last rise of water levels in the Neva in the 20th century happened in 1999. There is a certain regularity in the distribution of the floods. The probability of a flood with the level of over 185 centimetres above the zero water level increases in the years with minimum sun activity and on the ascending line of the 11-year Sun cycle. The influence of the century and half-century Sun cycles is also traced to the incidences of catastrophic floods. An extreme flood with rising of water 454 centimetres above the zero water level may happen in 2022-26. Such a flood is probable once in 1000 years. The probability of substantial floods in the near decades makes it necessary to accomplish the construction of the complex of protective installations.

References: Нежиховский Р. А. Вопросы гидрологии Невы и Невской губы. Л., 1988; Померанец К. С. Наводнения в Петербурге, 1703-1997 гг. СПб., 1998; Ловелиус Н. В. Ритмы увлажненности и наводнения в Санкт-Петербурге // Изв. РГО. 1999. Т. 131, вып. 1. С. 31-37; Антонов А. Е. Климатология экстраординарных невских наводнений и их прогнозирование. СПб., 2001.

I. G. Moskalenko. Bulgarin Faddei Venediktovich
Griboedov Alexander Sergeevich
Pushkin Alexander Sergeevich
Нежиховский Р. А. Вопросы гидрологии Невы и Невской губы. Л., 1988
Антонов А. Е. Климатология экстраординарных невских наводнений и их прогнозирование. СПб., 2001
Померанец К. С. Наводнения в Петербурге, 1703-1997 гг. СПб., 1998
Ловелиус Н.В. Ритмы увлажненности и наводнения в Санкт-Петербурге // Изв. РГО, 1999 Nevskie Gate
Siny Bridge
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