The Zuiderzee Works () is a system of dams and dikes, land reclamation and water drainage work, which was the largest hydraulic engineering project undertaken by the Netherlands during the twentieth century. The project involved the damming of the Zuiderzee, a large, shallow inlet of the North Sea, and the reclamation of land in the newly enclosed water using polders. Its main purposes are to improve flood protection and create additional land for agriculture.
The enormous scale of the works required the creation of a joint venture company comprising several large dredging contractors, known as the Maatschappij tot Uitvoering van Zuiderzeewerken. The American Society of Civil Engineers declared the works, together with the Delta Works in the South-West of the Netherlands, as among the Seven Wonders of the Modern World.http://www.ce.memphis.edu/1101/interesting_stuff/7wonders.html|Seven Wonders of the Modern World
Background The Low Countries have low flat topography, with half the land area below or less than above sea level, and have for centuries been subject to periodic flooding by the sea. The seventeenth century saw early proposals to tame and enclose the Zuiderzee, but the ambitious ideas were impractical given the technology then available.
From 1200 to 1900 AD the Dutch reclaimed of land from the sea and by draining lakes, a total of , but lost of land to the Zuiderzee. Hendrik Stevin in 1667 was the first to publish a study ("How the Fury of the North Sea may be stopped and Holland may be protected against it") proposing to drain the Zuiderzee. After the IJ and Haarlemmermeer were drained in the mid-19th century, van Diggelen, Kloppenburg, and Faddegon proposed that the Zuiderzee also be drained. Test drilling by the found that about three quarters of the Zuiderzee would be useful land. Plans were developed during the second half of the nineteenth century to protect areas from the force of the open sea and creating new agricultural land. Cornelis Lely (after whom Lelystad is named) was an ardent supporter, an engineer, and later government minister. A group called the "Zuider Zee Society" began a thorough investigation as to the best means of closing and draining the Zuider Zee in 1886, and in 1891 Lely introduced his plan, which formed the basis for the development of what were to become the Zuiderzee Works. It consisted of a large dam connecting the northern tip of North Holland with the western coast of Friesland and the creation of initially four polders in the northwest, the northeast, southeast (later split in two), and southwest of what would be renamed the IJsselmeer (IJssel-lake). Two major lanes of open water were defined for shipping and drainage. The initial body of water affected by the project was . Opposition came from fishermen along the Zuiderzee who would lose their livelihood, and from others in coastal areas along the more northerly Wadden Sea. They feared higher water levels as a result of the closure. Other critics doubted whether the project was feasible financially.
Queen Wilhelmina's speech from the throne in 1913 urged reclamation of the Zuiderzee, and the requisite bill was introduced. When Lely became Minister of Transport and Public Works that year, he used his position to promote the Zuiderzee Works and gained support. The government started developing official plans to enclose the Zuiderzee. On 13 and 14 January 1916 the dikes at several places along the Zuiderzee broke under the stress of a winter storm, and the land behind them flooded, as had often happened in previous centuries. This flooding provided the decisive impetus to implement the existing plans to tame the Zuiderzee. In addition, a threatening food shortage during the other stresses of World War I added to widespread support for the project. Lely stressed the importance of extending the area of arable land, and estimated that of good land would be reclaimed from the clay soil, while the regions with a sand bottom would eventually become the IJsselmeer.
On 14 June 1918, the Zuiderzee Act was passed. The goals of the Act were threefold:
Protect the central Netherlands from the effects of the North Sea; Increase the Dutch food supply by development and cultivation of new agricultural land; and Improve water management by creating a freshwater lake from the former uncontrolled salt water inlet.
Unlike earlier proposals the act intended to preserve part of the Zuiderzee and create large islands, as Lely warned that rerouting the rivers directly to the North Sea might cause inland flooding if storms raised the sea's level. He also wanted to preserve the Zee's fisheries, and for the new land to be accessible by water. The Dienst der Zuiderzeewerken (Zuiderzee Works Department), the government body responsible for overseeing the construction and initial management, was set up in May 1919. In the initial stages of the work heavy clay was dredged out of the open sea and deposited along the track to be followed by the dam. The cost of the undertaking was calculated in 1914, in UK currency, at about £19,000,000 but it soon seemed likely to be very much more. At the time, ten years were allowed for the construction of the main dam and another 20 years for the completion of the four inner enclosures.
The department decided against building the main dam first, proceeding to construct a smaller dam, the Amsteldiepdijk, across the Amsteldiep. This was the first step in rejoining the island of Wieringen to the North Holland mainland. The dike, with a length of , was built between 1920 and 1924. As with dike building, polder construction was tested on a small scale at the experimental polder at Andijk.
Construction phase
Enclosure
A new study, commissioned after doubts arose over the financial feasibility of the project, recommended that work should continue and be accelerated. The Zuiderzee Works Department initiated the next two major projects at the same time, in 1927. The most important of these was the main dam, the Afsluitdijk (enclosure dam), running from Den Oever on Wieringen to the village of Zurich in Friesland. It was to be 32 km long and 90 meters wide, rising to 7.25 meters above sea-level, with an incline of 25% on each side.
Experience showed that glacial till, rather than just sand or clay, was the best primary material for a structure like the Afsluitdijk. An added benefit was that it was easily available; it could be retrieved in large quantities by dredging it from the bottom of the Zuiderzee. Work started at four points: on both sides of the mainland and on two purpose-made construction-islands (Kornwerderzand and Breezanddijk) along the line of the future dam.
From these points, the dam was expanded as ships deposited till into the open sea in two parallel lines. Sand was poured between these two lines; as the fill emerged above the surface of the water, it was covered by another layer of till. The nascent dam was strengthened with basalt rocks and mats of willow switch at its base. The dam was finished by raising it with sand and finally clay for the upper surface of the dam, which was planted with grass.
Construction progressed better than expected. At three points along the line of the dam were underwater gullies, where the tidal current was much stronger than elsewhere. These had been considered major obstacles to completing the dam but proved not to be so. On 28 May 1932, two years earlier than forecast, the Zuiderzee was closed when the last tidal trench of the Vlieter was filled with a bucket of till. The IJsselmeer was born, though the lake still contained salt water at the time.
The dam was not finished. It still needed to be brought up to its full height, and a road linking Friesland and North Holland remained to be built. In addition to completing the dam, work needed was the construction of shipping locks and discharge sluices at the ends of the dam. The complex at Den Oever includes the Stevin lock and three series of five sluices for discharging the IJsselmeer into the Wadden Sea. The other complex at Kornwerderzand is composed of the Lorentz locks and two series of five sluices, making a total of 25 discharge sluices. Periodically discharging the lake is necessary since it is continually fed by rivers and streams (most notably the IJssel River, for which the lake is named) and polders draining excess water into the IJsselmeer.
The Afsluitdijk was opened 25 September 1933, with a monument marking the spot where the dam was finished. It used 23 million m3 of sand and 13.5 million m3 of till. An average of 4,000 to 5,000 workers were employed in the dam's construction, relieving unemployment during the Great Depression. The total cost of the dam was about €700 million (2004 equivalent).
ProjectDikeLengthStartClosureSizeDrainedConnection of the island of Wieringen to continental HollandAmsteldiepdijk2.5 km29 June 192031 July 1924——Closure of the ZuyderzeeAfsluitdijk32 kmJanuary 192723 May 1932——Pilot Polder Andijk-1.9 km1926Early 192740 ha27 August 1927Wieringermeer Polder-18 km192727 July 192920,000 ha31 August 1930Noordoostpolder-55 km193613 December 194048,000 ha9 September 1942Eastern Flevoland Polder-90 kmEarly 195013 September 195654,000 ha29 June 1957Southern Flevoland Polder-70 kmEarly 195925 October 196743,000 ha29 May 1968Marker Wadden PolderHoutribdijk28 kmLate 2012The project is still under construction as of 2021. The first island was completed in late 2020.2,500 ha24 September 2016
Land reclamation After damming off the sea, the next step involved creating new land, known as polders. This was achieved by damming off portions of the IJsselmeer, and then pumping all the water out. The first polder, Wieringermeer, was dammed in 1929 and fully drained in 1930. The third, the Noordoostpolder, was not fully drained until 1942. It was an area much used by the Dutch Underground resistance during World War II, as the fresh polder offered numerous hiding places.
After the war, work was started on draining the Flevolands, a massive project totalling almost 1000 km2. This area is now home to Lelystad and Almere; the latter is the fastest growing city in the Netherlands (in part because of its proximity to Amsterdam). Another large polder was originally planned in the Markermeer. This project was extensively debated until plans were abandoned in the early 2000s, as environmental issues were viewed differently than in the 1920s. A new province, Flevoland, was created out of the Noordoostpolder and the Flevolands in 1986, thereby completing the Works.
This new land led to an identity change for towns including Lemmer, Vollenhove, Blokzijl due to losing their direct access to the sea and Kuinre was completely cut off from open water. The former islands of Urk and Schokland, and Wieringen got connected to the mainland.
The other major project started in 1927 was the construction of the polder in the northwest, the first and the smallest of the five projected polders. It replaced the Wieringermeer, the body of water south of Wieringen, and also the name of the new polder. It was the only polder reclaimed from the Zuiderzee itself (the others were reclaimed after the Afsluitdijk was finished), but it wasn't entirely the first. A small test polder of some 0.4 km2 was constructed in 19261927 near Andijk in North Holland to research the effects drainage would have on the soil of the Zuiderzee and how best to configure the new polders.