Pretzien Weir

Description

The Pretzien Weir, a sluice gate weir completed in 1875, is located at the banks of the river Elbe in the vicinity of the city of Magdeburg. The Elbe river is one of the major streams of Central Europe. Periodic floods in this largely unregulated river frequently alter the water level at Magdeburg from 0,5 meters in times of draught to 7,5 meters in times of high flooding, an enormous challenge for cities an settlements nearby. The weir is the central part of a spacious flood bypass system for the region. In the case of flooding the weir is opened, allowing a relief of up to 1.200 cubic meters per second of the river waters into a diversion canal, which equals about 1/4 of the water volume of the Elbe in times of flood. Through this canal the water bypasses the nearby cities of Magdeburg and Schönebeck and the rural areas nearby. Around 400.000 people rely on the protection of the Pretzien Weir today.

As the weir remains closed as long as water levels are low or moderate, it allows for a reliable water depth in the Elbe river to enable shipping. The function of the weir is thus twofold: it enables shipping traffic in the main riverbed, and also offers effective protection against high floods for the region since 1875 into the present.

The Pretzien Weir is a sluice gate weir featuring moveable sluice gates or flashboards made of cast iron, held by vertical iron stands which are also moveable when the weir is opened (in German: Schützenwehr mit beweglichen Losständern). As terminology differs internationally, it may also be considered a floodgate in some countries. This genius work of engineering constitutes a groundbreaking technical development that was to shape further flood protection structures throughout Europe in the late 19th century.

The weir consists of a massive structure with eight pillars and a bridge resting on top of them. These pillars rest on a substructure, which is a single body: 162.80 meters long, 7.50 meters wide and 3.80 meters high. Its lowest part, the foundation, 1.20 meters high, is made of concrete. Above the foundation a layer of quarry stone masonry with a 0.30 to 0.50 meter thick cover forms a broad water bed to sustain the water pressure when the weir is opened.  

On this substructure, eight pillars and two abutments with their semicircular foreheads form nine weir openings with a width of 12.55 meters each. The pillars are 2.22 meters wide at the top and 2.51 meters at the bottom - the difference is used for the attachment of the outer slide rails for the protection boards. The pillars are made of quarry stone masonry (limestone from Bernburg), while all outer parts of the pillars are covered with sandstone workpieces from Saxony. The sandstone tiles are an impressive part of the architectural language of the weir, clearly derived from the period of historicism. The design follows the structural requirements of engineering without missing the demands placed on representative public buildings. The rounded pillars of the Pretzien Weir not only fulfill their static function, they are also likened to the appearance of medieval fortifications. With their forceful appearance and their foreheads decorated with cornices, they appear extremely defensive, without hiding their technical purpose. The system is an expression of the self-confidence of engineering and the inventive spirit in the industrial age in Central Europe. 

On the downstream side, the top edge of the pillars is 7.95 meters high; on the upstream side it is 7.35 meters. The masonry supports a bridge at a height of 4.77 meters above the ridge of the weir. Movable iron stands, in between which the sluice gates/flashboards can be drawn up and down, are suspended from the bridge. In order to absorb the considerable horizontal thrust of the dammed water, the bridge bearings are connected to one another and firmly anchored by split pins in the head of the piers. For greater safety, the pillars were reinforced with masonry up to the lower edge of the bridge pavement and crowned with heavy sandstone workpieces. 

On the bridge, the plank coverings of the 112.50 meter long bridge are 0.40 meters apart, leaving a gap in the middle. This slot in between is used to insert and remove the sluice gates/flashboards. Winches mounted on wagons help to raise and lower the boards, as the wagons can be easily moved back and forth on rails mounted on both sides of the slot. 

The movable locks of the Pretzien Weir are made up of vertical iron stands and a great number of flashboards. The layout of each opening shows eight iron posts and two sandstone pillars, accounting for nine openings. When the weir is closed, the flashboards are lowered in four rows one above the other between the stands and the pillars, which equals 36 pieces per opening. 

The 324 flashboards weigh 100 kilograms each. They are 1.31 meters long and 0.84 meters high, and consist of 6 millimeters thick, iron-framed metal buckles. Originally, the flashboards were moved along the iron posts in grooves and therefore froze easily during winter floods. This detail was changed as early as 1881 in order to keep the weir operable in cold temperature. Since then the boards have only been supported against a fold and are therefore easier to move in frosty conditions.In each weir opening there are eight moveable iron posts. When the weir is closed, each post is fixed in a heavy iron safety shoe - secured with a movable pawl and a pin. A large part of the water pressure is thereby transferred to the back of the weir itself, a first-time application of this new type of notching device for weirs, which contemporaries highlighted as a highly innovative engineering achievement.The flashboards are lifted with the help of the winches moving over the slot. To do this, the wire ropes attached to the boards are hooked onto the winch, the boards are then pulled up and placed next to each other on the bridge. In 1884, the duration of opening or closing the entire weir with 20 workers was estimated to be around eight hours.

Justification of Outstanding Universal Value

The weir system in Pretzien is an extraordinary structure in the flood protection system of the Elbe river close to the town of Schönebeck in Saxony-Anhalt, in the middle of Germany. In the broad glacial valley of the river, it initially flowed in many meanders to the north, but shifted further and further west, frequently threatening the two cities of Schönebeck and Magdeburg. Conventional dykes could only provide inadequate protection. At the same time, the strongly fluctuating water level hindered river navigation. As a regulating measure, Hermann Wurffbain from the Prussian building administration developed a large-scale landscape project, in which a 21 km long flood channel could bypass parts of the water mass of the Elbe past the cities. The weir system in Pretzien serves to regulate the inflow, so as to create a dam during the summer months to elevate water levels in the river bed for shipping, and to bypass floods when needed into the channel.  

For the construction of this weir, the known principle of the sluice gate weir had to be further developed in new dimensions and for new demands - especially when facing ice drifts at the weir. After improvements to technical details in the first years of its operation, the construction of the Pretzien Weir was so successful, that it still meets the requirements today. After its construction, the weir system was published internationally in journals and presented at exhibitions around the globe. The conception and construction of the Pretzien Weir was so mature that it has remained fully functional over a period of 150 and is still in use. This work of engineering became a worldwide model for dozens of similarly demanding tasks in flood control, but is still exceptional in its dimensions and unique in its state of preservation and function. All known successors of the Pretzien weir – sluice gate weirs with movable stands from the late 19th century - have since been replaced by more modern systems from the 20th century. Only Pretzien as the model and origin of this formative engineering achievement has survived. 

The design of the weir follows the structural requirements of engineering, but goes far beyond in its architecture. With their bulky sandstone applications and their foreheads decorated with cornices, the rounded pillars look like castle battlements and appear extremely defensive, without hiding their technical purpose. The system is thus an expression of the self-confidence of engineering technology and the inventive spirit in the industrial age, it combines ingenious technical innovation with the contemporary architectural language of Historicism.

Criterion (ii): The flood protection system of the Elbe with the Pretzien Weir as its central component exhibits for a span of time - the 19th century and until today - within a cultural area of the World - Central Europe - an important interchange of human values ​​with regard to flood protection, engineering achievements in the age of Industrialism, the development of the necessary technical facilities and the associated landscape design.

Criterion (iv): The Pretzien Weir is an outstanding technological ensemble that symbolizes a significant period in human history. It represents the development and first-time use of a large-scale system for river flood protection in a wide area, Its construction has remained fully functional to this day over a period of 150 years. The Pretzien Weir as a model for many other plants throughout Europe marks a high point of the industrial age in the field of engineering.

Statements of authenticity and/or integrity

Authenticity
The Pretzien Weir is authentically preserved in form and function. The maintenance and repair measures required due to continuous use do not affect the authenticity of the objects.In 2010, after 130 years of operation, the weir structure had to undergo a comprehensive repair, which was carried out in accordance with monument preservation specifications as advides by the competent authorities; in this repair the appearance, function and technology of the weir were fully preserved. The sandstone and limestone parts of the weir were repaired and partly replaced using natural stones of the same origin as before. Heavily stressed iron components, mostly made of 19th century puddle steel which tends to turn brittle over time, have been repaired with some modern steel additions in their original form and function. 

Integrity
The flood protection system of the Elbe river with the Pretzien Weir east of Schönebeck and Magdeburg has been completely preserved, changes have not been made and are also not expected. The area around the weir is well protected by numerous legal requirements, as no structures may be erected in this flood area. All parts of the proposed property are protected as cultural monuments and also designated a biosphere that is recognized and protected by UNESCO’s Man and Biosphere Programme (MaB). An impairment of the existing lines of sight is therefore not possible. The facilities will continue to be used and maintained as originally planned.

Comparison with other similar properties

No individual weirs have so far been listed as UNESCO World Heritage, nor has any State submitted a weir as part of a tentative list.  

Movable weirs have been used in Central Europe for around 1,000 years, especially for operating watermills. The oldest construction is the wooden beam weir: wooden beams are placed horizontally between vertical guide elements, groats or piers; this wooden wall holds back the water. Such beams are heavy and their joints are leaky. In addition, they are difficult to remove in the event of flooding, the construction can hardly be regulated and only allows the construction of small weirs.
Sluice gate weirs basically function like wooden beam weirs, in which the closures held by the weir wall can be pulled up and opened with the help of a winch over a chain, rope or rack, even during floods. Wooden boards combined to form sluice gates, and, since the 19th century, also iron plates are used to close the dam. Larger openings were divided up with a large number of pillars, posts, and metal stands. 

The design of the needle dam-type weir (also referred to as deedle-dams) is also very old. Here the water is dammed with a long row of vertically set up poles made of wood or metal, which are almost vertically next to each other and lean against a the pier of the weir system. Only a few examples of this once widespread type of defense have survived: in Germany on the lower Havel, on the upper Spree and on the Werra in Hann. Münden and the Ilmenau below Lüneburg. These structures did not meet the requirements for larger weir structures and large water bodies like the Elbe river.

At the beginning of the 20th century, electricity replaced manual work: This instance and also a considerably improved steel quality led to weirs with large steel structures. These modern structures are more resistant to water pressure. They are usually moved around a horizontal axis using machine power. Instead of a straight gate, segment weirs have a curved body; they are rotated around their horizontal axis. In the widespread case of roller weirs, a cylinder is moved on an inclined roller path. The water flows over it, as do the hollow bodies of sector weirs. The weir in the Elbe near Geesthacht, which was commissioned in 1960, is one of the large weirs of this type: the four sectors in the four openings are each 50 meters wide. These weir types would be impossible to operate without electricity, making them scarcely comparable to the structures of the 19th century. 

The Pretzien Weir was at the time of its construction - and still is – the largest sluice gate weir in Europe. It was a model for many similar structures.
A weir system comparable in several respects to the Pretzien Weir was put into operation in 1858 near Hohensaaten in the Oder river in Germany, which was constructed as a complex system with a sluice weir and stem gates. In 1913 it was taken out of service and immediately demolished. 

Similar cases are to be found in France. In order to improve shipping in the Seine river, it was first canalized between 1838 and 1866 with seven barrages. After a few years, a renovation based on the Pretzien model began at the weirs below Paris. Only the weir between Amfreville and Poses from 1887 has remained in its basic concept until today, even though large parts of the weir have been demolished in favor of a hydropower plant.

Austrian engineers were also impressed by the weirs at Poses and Pretzien and created a similar system as the upper end of the Danube Canal in Vienna: the Nussdorf Weir. The arm of the Danube river running through the city was thus protected from flooding and provided conditions for shipping. From 1894 to 1899 the weir and an additional lock were built. The Nussdorf weir is known today primarily because of the architect Otto Wagner, who designed the representative architecture of the structure. The weir was designed for a storage height of 9.34 meters with a width of 40 meters. In order to withstand the water pressure and to carry the heavy construction with the sluices, the reinforced and very stable Schemerl Bridge over the weir was constructed, which is also used for road traffic. The weir featured 33 stands that could be pulled up manually with chains, similar to the original construction in Pretzien. The sluice gate weir was eventually replaced by a two-part segment weir from 1971 to 1975. Only the old bridge was largely preserved.

The small weir in the Bocholter Aa in Germany was also modeled after the Pretzien Weir, but important details were changed significantly by the government architect Julius Jerike. The weir, built in 1897 according to a design by Jerike on behalf of the city of Bocholt, had a width of 15.80 meters. In each of the ten openings there was only one 2.20 meter high and 1.49 meter wide sluice gate/flashboard. In 1965 the structure was replaced by a new weir entirely.

In the Austrian Empire, other weirs were built based on the Pretzien model, for example the structure in Miřowitz near Mühlhausen in the Moldau river in Bohemia (now Miřejovice near Nelahozeves), which was completed in 1904. This system was already to be operated with electrical winches. “Despite the exemplary arrangement of this weir in the details, it cannot withstand competition with the cylindrical weirs and should not be rebuilt,” commented Otto Franzius in 1927, Professor of Hydraulic Engineering in Hanover, on the construction.

Far more smaller structures were errected after the model of Pretzien in Central Europe. In addition to the fixed weir in the Ems river near Hanekenfähr in Germany, a sluice gate weir like the one in Pretzien was built. And near Arnsberg in the Ruhr river in Germany, there was also a Pretzien-style system. There were also improved versions of the Pretzien Weir in the Mulde river near Bitterfeld in Germany to be found, as well as in the Weser river near Dörverden/Germany, and in Ransern near Breslau/Poland in the Oder river. They have all been destroyed and replaced in past years.

Noteworthy modern successors to the Pretzien Weir are the two systems of the Quitzöbel Weir Group, errected from 1936 to 1954 below the city of Havelberg/Germany at the confluence of the Havel river into the Elbe river. These weirs with their huge roller gates, which can be operated in both directions, show how quickly structural engineering and mechanical engineering have developed since the Pretzien Weir was commissioned. The Quitzöbel Group has been extensively renovated since 2009. However, the old weir that was partly comparable to Pretzien was replaced by a similar new building.  

The concept of the Pretzien Weir as a sluice gate weir has not been used for large water defense systems since the First World War at the latest. It is still described in specialist literature until around 1930, after which it is only viewed in retrospect in individual representations.

So far, the World Heritage List does not contain any weirs as individual objects, resulting in a noteworthy gap regarding these advanced technical monuments and feats of engineering in the 19th century.

The World Heritage in the Netherlands however does include numerous flood-related structures. A larger system is the more than 200 km long "Water Defense Line", a coherent system developed over the long period between 1815 and 1940, with which in wartime deliberate floods could be brought about to ward off enemy incursions. Naturally, this includes many systems for regulating water levels and tributaries. The concept here, however, is the decentralized control at numerous points with smaller dams and weir systems as well as pumping systems, canals, ditches, and polders. This also includes a larger weir system with simple flashboards, which is considerably younger than the Pretzien Weir. 

Augsburg's water management system, which has been part of the World Heritage since 2019 and which combines numerous hydraulic engineering systems, has a large weir system comparable to that of Pretzien, the so-called High Drain in the Lech river. It was built in 1911/12 after a major flood at the site and serves to drain Lech river water into the city's canals. With its construction as a reinforced concrete structure with roller weirs (or roller dams), it belongs to the successor generation of the Pretzien Weir, which is technically only remotely comparable with this one.