Water

The hydrological dominant of Prague, the Vltava, is the longest Czech river. Its length is 430.2 km, the area of its basin covers 29 090 sq. km, the mean flow rate at the mouth is 149.9 cu.m./s. Below its confluence with the Berounka and, consequently in the territory of Prague, the area of its basin is 26 689.12 sq.km and the mean long-term flow rate is 147.5 cu.m./s. These data show that this river has been and is the decisive factor of landscape and natural conditions formation. Particularly great was the impact of floods during which often considerable parts of the city were under water, new islands originated and other disappeared.

Map of water courses and water surfaces in Prague (based on the data of IMI Prague).

The evaluated flow rate in Prague on September 6, 1890, viz. 3 975 cu.m/s (with water level of 506 cm above normal) is usually considered the historical (centennial) flood.

The second largest water course in the territory of Prague is the Berounka, the left-hand tributary of the Vltava in Lahovice. It is 139.1 km long and has a basin are a of 8 861.4 sq.km. Its mean flow rate at its confluence with the Vltava is 36 cu.m/s.
Although the Vltava is the biggest water course in Prague, also the Labe (Elbe) flows nearby and the northern and northeastern part of the city is drained by the Mratín, Vinoř and Jirny Brooks to it. There are more than 70 brooks in the area of Prague, the total length of which exceeds
300 km; their joint basin of 100 sq.km slopes towards the Labe. On the right-hand side the Vltava has 33 brooks some 100 km long, on the left-hand side 42 brooks some 200 km long.

From the number of most important brooks mention should be made of the Botič, springing near Křížkovský Újezdec, district Prague-East; it is 33.5 km long and has a basin of 134.85 sq.km.
The Dalej (sometimes also Prokop) Brook springs in Chrášťany, district Prague-West. It is 13.5 km long and has a basin of 36.8 sq.km.
The Jirny Brook, springing in Horní Počernice, is 11.8 km long and has a basin of 32.8 sq.km.
The Kunratice Brook, springing in Vestec nr. Jesenice, district Prague-West, is 14.9 km long with a basin of 31.6 sq.km.
The Mratín Brook (also called Ďáblice Brook in its upper course) springs in Ďáblice and flows directly to the Labe. It is 15.22 km long and has a basin of 74.4 sq.km.
The Pitkovice Brook springing near Předboř, district Prague-East, is 14.4 km long and has a basin of 31.4 sq.km.
The Radotín Brook springing near Ptice, district Prague-West, is 22.6 km long and has a basin of 68.5 sq.km.
The Rokytka, springing near Tehovec, district Prague-East, is 26.2 km long and has a basin of 140 sq.km.
The Říčany Brook (also called Říčanka), springing near Tehov, district Prague-East, is 21 km long and has a basin of 37.5 sq.km.
The Šárka Brook, springing near Chýně, district Prague-West, is 19.5 km long and has a basin of 62.9 sq.km.
The Únětice Brook, springing near Kněževes, district Prague-West, is 13.4 km long and has a basin of 47.6 sq.km.
The Vinoř Brook, springing in Kbely, is 12.9 km long and has a basin of 40.52 sq. km.

The above brief survey shows that the most important brook in Prague is the Rokytka. However, even smaller brooks are of great significance both by their contribution to the formation of Prague landscape and by the generation of specific biotopes of individual localities and influence on the microclimate in their environs.

Also water reservoirs, i.e. ponds, recreation and other reservoirs, are landscape-forming elements. The best known are the recreation reservoirs in Hostivař on the Botič and in Džbán on the Šárka Brook.
Hostivař reservoir on the Botič on the SE outskirts of Prague is generated by an earth dam 16 m high and 110 m long. The area of the reservoir is 43.8 ha, maximum depth 12 m, constant volume 1.34 mill. cu.m, total volume 2.13 mill. cu.m., length 2.6 km, maximum water level at 249.00 m above sea level. It is used for recreation, swimming and angling. The dam was completed in 1962. The brook basin above the dam covers 94.8 sq.km. The mean annual flow rate is 0.350 cu.m/s.
Džbán reservoir on the Šárka Brook in Vokovice is generated by an earth dam 8.5 m high and 75 m long. The reservoir area is 18 ha, its total volume 0.433 mill. cu.m, maximum depth 7.5 m, length 0.8 km. The reservoir is used for recreation, swimming and angling.
Počernice Pond on the Rokytka is situated on the eastern end of Dolní Počernice. It has an area of 17 ha and is intended for recreation (swimming). The basin area above the dyke covers 87.1 sq.km. The mean annual flow rate is 0.276 cu.m./s. The earth dyke is 360 m long and 5.2 m high. It is the biggest pond in Prague.
Podlesí Pond on the Říčany Brook in Uhříněves, with an area of 14.14 ha, is the second largest pond in Prague. It has a volume of 355 000 cu.m. The dyke is 200 m long and 5 m high.

The significance of water courses and reservoirs is testified to also by the fact that most natural parks in Prague have a water course as a natural axis, as well as the fact that numerous protected areas in Prague are situated in water course valleys, as you will see in further parts of this publication.

In conclusion let us mention the temperature regime of the Vltava which was changed significantly by the construction of the Vltava cascade. Particularly its last step, the Vrané dam, influences the temperature regime of the river by the discharge of its lowest water. In the summer it cools the water in the river, in the winter it warms it up. This arouses the displeasure of both the recreants and young people, because the Vltava does not freeze mostly in winter which influences the practice of winter sports. On the other hand, this circumstance has turned the Vltava in Prague into an important wintering site of numerous birds.

Aerial view of the ponds and reservoirs in the environs of Milíčov with the Hostivař reservoir, the largest water surface in Prague, in the background.

A role of great importance in the Hrnčířské Louky (PP) is played by a group of ponds contributing to adequate water regime of the protected area.

The slopes of Petřín have a number of springs.

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