Hydrographic network

Рубрикатор / City Topography/Nature and Natural Phenomena
HYDROGRAPHIC NETWORK. The hydrographic system of the precincts of St. Petersburg is formed by nearly 20,000 water flows, practically all of them pertaining to the Neva River basin. The total length of the currents exceeds 100,000 kilometres. The streams are evenly distributed over the region, forming a tracery network of meandering channels with constantly running water. St. Petersburg comprises about 100 rivers, streams and channels, over 20 canals and over 100 lakes and ponds within its limits. The total length of rivers and canals approximates 300 kilometres, while the area of the water surface reaches up to one tenth of the area of St. Petersburg. The Neva delta occupies an area of 83 square kilometres, with a length of 32 kilometres within the limits of St. Petersburg. The major river of the area is the Neva, which is joined by the basins of Lake Ladoga and the Gulf of Finland. The second largest river of the region is the Svir, connecting Lake Onega and Lake Ladoga, with a length of 224 kilometres. Its catchment area equals 83,200 square kilometres, the average width varies from 180 metres to 200 metres, and the depth amounts to 5-8 metres. Its average annual flow rate reaches up to 790 cubic metres per second, and the stream velocity is approximately 1.3-1.5 metres per second. The Volkhov river also appears significant for the water balance. It also links two reservoirs, Lake Ilmen and Lake Ladoga. The Volkhov is 224 kilometres long, with the catchment area of 80,200 square kilometres and average annual flow rate of 590 cubic metres per second. The intrinsic feature of the Volkhov consists in the acute fluctuations of the water level, especially in the time of spring tide, when the discharge rate increases nearly 70 times. The major river of the Karelian Isthmus is the Vuoksi (Vuoksa) River, which runs from Lake Saimaa to Lake Ladoga. The river is 153 kilometres long, with the catchment area of 68,000 square kilometres and the average discharge rate at the river mouth amounting to 68 cubic metres per second. The minor rivers of the Neva basin include the Mga, Tosna, Izhora, Slavyanka and Okhta. A number of rivers flow directly into the Gulf of Finland; among them the Luga River (353 kilometres long, with an average flow rate of approximately 100 cubic metres per second), the Kovashi River, the Sista River on the south, the Sestra River and the Roshchinka River on the north are most significant. The nourishment of the rivers of the southern part of the area is mainly supplied by ground water, associated with karst and artesian aquifers contained in Palaeozoic rocks. The rivers of the Karelian Isthmus are supplied by snow, rain, and swamps. In summer, water in the rivers warms up to 22 degrees Celsius, while the average temperature rate does not exceed 18-19 degrees Celsius. Winter freezing-over lasts for four months, with the thickness of ice cover varying from 30 centimetres to 90 centimetres. The Neva is characterised by double drifting of ice: the earlier one occurs due to the melting of river ice, while the later ice-drifting is determined by the floating of Lake Ladoga ice. The characteristic feature of the hydrographic system of the precincts of St. Petersburg is numerous lakes. Their number within the limits of Leningrad Region approximates 1,800, while the total area occupies 14% of the area of the region. Most of the lakes have glacial origin, with clear and pure waters. The major lakes of St. Petersburg owe their origin to the depressions between kames (Suzdalskie Lakes) or karst-erosional deepening of the edges of the escarpment (Lake Duderhof, or Lake Dudergofskoe). Near St. Petersburg, there is Lake Ladoga, which is the largest freshwater basin in Europe. The coast of the Gulf of Finland and its eastern end, the Neva Bay, accommodates a number of palace and park ensembles, health centres, holiday homes and numerous summer houses. The waters of the gulf, slightly saline and comparatively clear west of the alignment of Kotlin Island, have great recreational value. The sea breeze, almost constantly blowing here, sets up favourable conditions, freshening up the air and saturating it with sea-salt. Sea turbulence is usually slight here, and the ebb of waves renews the sandy beaches, especially those of the northern shores. The other peculiarity of the hydrographic system of the area lies in the large number of swamps; nearly all the marshes within the limits of St. Petersburg have been drained, while those on the immediate surroundings of the city form natural landscapes. The swamps divide into upland ones with woodless surface or sparse pine-tree planting, with practically no visible water, and lowland moors, grassy-reed with few trees and vast spaces of water. Like lakes, swamps are of great importance for regulating the water balance, as well as for the animals and birds of the area. The hydrographic system is economically developed, with a number of hydroelectric power plants (Volkhov Hydroelectric Power Plant, Svir Hydroelectric Power Plants), and a significant number of dikes and dams comprising ponds and storage pools; most of the rivers are navigable. The Neva River, the Svir River and Lake Ladoga form a part of the Volga-Baltic Water System and the White Sea-Baltic Water System. Practically all the reservoirs are used both for water-supply and for technical purposes. Sewage disposal facilities are few in number in the towns and villages of the region, which results in the pollution of the reservoirs and causes complicated ecological situations. St. Petersburg still faces incomplete purification of surface water due to the insufficient output of sewage disposal facilities. Almost everywhere within the limits of St. Petersburg, the hydrographic system has suffered significant changes as a result of territorial development and city building. During 300 years, the number of lakes in St. Petersburg has been reduced from 101 to 41, whereas the quantity of rivers and canals has reduced by one third in the past 200 years. The configuration and functioning of the branches of the Neva delta, together with embankments faced with granite, have also changed. Similar modifications have partly affected the banks of the Neva Bay, too; above all, it was determined by the soil filling and hydraulic deposition of soil during the building of port constructions, construction of Morskoy Canal, and the building of purification and treatment facilities and residential areas on Vasilievsky Island and in Staraya Derevnya. A new hydrographic system has emerged in the south-west of St. Petersburg and in the vicinity of Lake Dolgoe.

References: Ильина Л. Л., Родионов В. З. Воды и веси: (Экол.-ист. очерк). СПб., 1997.

Y. P. Seliverstov.