Pretziener Weir

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Pretziener Weir

The Pretziener weir near the town of Pretzien is part of a dyke system to protect the cities of Magdeburg and Schönebeck from flooding of the Elbe . After the weir has been opened , up to a quarter of the outflow of the Elbe is diverted over the Elbe flood canal via Biederitz east of Magdeburg and Schönebeck.

Planning and construction

The Elbe runs at the level of the Pretziener weir in a six to eight kilometer wide glacial valley , in which the course of the river would constantly change without human intervention to form meanders . Before the 10th century, the Elbe ran on the eastern edge of the glacial valley along a ridge from Dornburg to Hohenwarthe . In the following centuries the Elbe shifted westwards towards Schönebeck and Magdeburg. An intermittent river course from Ranies via Grünewalde and Randau to Salbke has been preserved as the Old Elbe .

A proposal for the construction of a flood canal was contained in the memorandum in the so-called Elbenau dyke regulation matter of 1865, which arose with the significant participation of the Prussian civil engineer Hermann Wurffbain (1804-1889). The canal was to follow the old course of the Elbe on the eastern edge of the glacial valley. The discharge through the canal was supposed to be regulated by a fixed weir at Pretzien. The weir was supposed to prevent the river from flowing through the old Elbe at low and medium tide, which also benefited Elbe shipping. Smaller floods were supposed to flow away via the Elbe, which enabled more intensive agricultural use of the areas in the flood canal. In the event of major floods, the canal should relieve the Elbe and thus protect the cities of Magdeburg and Schönebeck. A law to build a weir and canal was passed in July 1868. In 1869 the plans were modified to the effect that the Pretziener weir should be built as a movable weir .

Construction of the flood canal began in 1869; In 1873 it was largely completed. The foundations of the weir were built in 1871; In 1875 the weir was operational. Little is known about the construction work as there are no contemporary publications. The proportion of manual labor was probably high. The overall project, which was headed by Hermann Wurffbain, also included 3,000 French prisoners of war from the Franco-German War .

Building

A yoke of the weir

The weir is part of an approximately 900 meter long transverse dam in the Elbe flood canal. The sandstone substructure of the plant is 162.8 meters long, 7.5 meters wide and 3.8 meters high. There are two abutments and eight central pillars 5.75 meters high. Between the abutments and pillars there are nine yokes with a clear width of 12.55 meters; the usable flow width is thus 112.95 meters. Each yoke is divided by eight loose posts and locked by 36 iron rifle boards. To protect against scouring , there is an eight-meter-wide fall bed below the weir.

The rifle boards, each weighing 100 kilograms and measuring 1.31 by 0.83 meters, can be pulled upwards. To do this, two electrically operated winches are pushed on tracks from yoke to yoke and the rifle boards are pulled up individually using cables. The free-standing loose stands are notched with a hand winch and bent upwards to allow floating debris and any ice floes to flow freely through.

use

During a flood in February 1876, it was only possible to open a third of the weir, as the protective boards and loose stands were frozen to a thick sheet of ice. The free outflow of the Elbe water until the weir was built was impeded by the weir, and the water level above the weir rose. As a result, the Elbe dike on the left near Glinde broke, flooding the town of Schönebeck and damaging a large part of the houses there. The flood caused severe damage to the Pretziener weir. Among other things, the lintel bed below the weir was too weakly dimensioned, as a result of which puddles formed, which caused three weir pillars to collapse.

After the flood of 1876, the damage to the weir was repaired and the fall bed reinforced. In 1879 the Dornburger Siel was built in the Querdamm near Pretzien. It drains the Dornburg lowlands, the receiving water of which was impaired by the construction of the dam. In 1880 and 1881, a newly developed release device was installed for the weir's loose stands, which remained functional even when the ice fell.

The control of the weir led to conflicts between those above and below, which arose during the construction of the weir and continued in 1899. From the point of view of the upstairs, opening the weir as early as possible and thus more frequently was desirable, as this relieved the pressure on their own dykes and reduced the amount of pressure water . Because of the use of the flood channel and because of the interruption of traffic routes such as today's federal road 246a between Schönebeck and Plötzky , people below advocated a late opening of the weir. The conflicts were further exacerbated by the fact that a large part of the communities above the weir belonged to Anhalt , the places below mostly to the Prussian province of Saxony .

After the problems with the flood in 1876, the weir was partly left completely open in the following winters. Since December 1881, the operation of the weir has been regulated by a decree, the main features of which are still valid today: The weir is opened when the water level in Barby has reached or is definitely exceeded at 5.92 meters. When the water level in Barby drops below 5.25 meters, the weir will be closed.

The weir opened on June 3, 2013

When the weir is opened, the top row of protection panels is usually removed first. This creates a cushion of water below the weir, which reduces the risk of scour formation. Then, starting in the middle, the yoke is opened completely. Opening today takes around five hours with 16 employees.

The weir gained nationwide fame during the Elbe floods in August 2002 , when the Elbe and some of its tributaries flooded large parts of Saxony and Saxony-Anhalt . According to measurements on August 19, 2002, around 1050 cubic meters per second flowed through the flood channel. This was equivalent to 24 percent of the runoff in Barby. Using the canal sank the water level in Schönebeck by 70 centimeters and in Magdeburg by 50 centimeters. The theoretical capacity of the flood canal is given as 1200 cubic meters per second.

Because of the heavy pollution from the floods of 2002, the operator of the weir, the State Office for Flood Protection and Water Management Saxony-Anhalt , considered a fundamental renovation of the Pretziener weir to be necessary. In 2003 and 2004 the abutments were renovated; In 2010, steel components, the masonry of the pillars and the electrical system were renewed in accordance with listed buildings. The weir had already been renovated in 1959 and 1960; at that time a ten-meter-deep sheet pile wall was installed above the weir. In addition, cavities were grouted with concrete.

The opening of the weir when the Elbe flooded on June 3, 2013 was roughly the 64th opening of the weir. The vast majority of the weir openings took place in the winter half-year.

When it was completed in 1875, the Pretziener weir was the largest rifle defense in Europe. It served as a model for similar weirs, for example for the Nussdorf weir in Vienna. Weir and flood canal are also an integral part of international specialist literature. In 2004 the city of Magdeburg dedicated a memorial stone to the builders of the Pretziener weir to the flood of 2002. A detailed model of a weir yoke on a scale of 1:10 is in the German Museum of Technology in Berlin . In 2015, the Federal Chamber of Engineers named the weir as a historical landmark of engineering in Germany .

literature

  • Sven Bardua: The Pretziener weir on the Elbe. (= Historical Landmarks of Civil Engineering in Germany , Volume 17) Federal Chamber of Engineers , Berlin 2015, ISBN 978-3-941867-16-1 .
  • Hermann Mathies: The improvement of the Elbe lowlands near Magdeburg and the weir near Pretzien. In: Centralblatt der Bauverwaltung 4 (1884)

Web links

Commons : Pretziener Wehr  - Collection of images, videos and audio files

Individual evidence

  1. ↑ Bardura, Pretziener Wehr , p. 9 f.
  2. ↑ Bardura, Pretziener Wehr , pp. 16 f, 38.
  3. ↑ Bardura, Pretziener Wehr , pp. 19-21.
  4. ↑ Bardura, Pretziener Wehr , pp. 30, 32–34, 37.
  5. ↑ Bardura, Pretziener Wehr , p. 46.
  6. ↑ a b Bardura, Pretziener Wehr , p. 55.
  7. ↑ Bardura, Pretziener Wehr , p. 56.
  8. ↑ Bardura, Pretziener Wehr , pp. 49–52.
  9. ↑ Bardura, Pretziener Wehr , p. 58 f.
  10. ↑ Bardura, Pretziener Wehr , p. 60 f.
  11. ↑ Bardura, Pretziener Wehr , pp. 89–92.
  12. ↑ Table of weir openings at www.pretziener-wehr.de , also printed by Bardura, Pretziener Wehr , p. 97. According to Bardura, the information is “not always correct based on the latest findings”. (Footnote 140, p. 103).
  13. ↑ Bardura, Pretziener Wehr , pp. 6, 63, 72-74.
  14. ↑ The Pretziener weir on the Elbe at Wahrzeichen.ingenieurbaukunst.de (accessed on July 24, 2016).

Coordinates: 52 ° 2 ′ 21.1 ″  N , 11 ° 49 ′ 41.2 ″  E