Editing Zuiderzee Works (section)

===Enclosure===
[[Image:NL-Zuiderzeeworks.svg|right|thumb|The Zuiderzee Works in the Netherlands divided the dangerous Zuiderzee, a shallow inlet of the North Sea, into the tame lakes of [[IJsselmeer]] and [[Markermeer]], and created 1650&nbsp;km<sup>2</sup> of land.]]
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&nbsp;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 [[till|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 [[Canal lock|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 ''[[Hendrik Lorentz|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&nbsp;million m<sup>3</sup> of sand and 13.5&nbsp;million m<sup>3</sup> 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 [[euro|€]]700 million (2004 equivalent).

{| class="wikitable" 
|-
|bgcolor="lightgrey"|Project
|bgcolor="lightgrey"|Dike
|bgcolor="lightgrey"|Length
|bgcolor="lightgrey"|Start
|bgcolor="lightgrey"|Closure
|bgcolor="lightgrey"|Size
|bgcolor="lightgrey"|Drained
|-
|Connection of the island of [[Wieringen]] to continental Holland
|align="center"|[[Amsteldiepdijk]]
|align="center"|2.5&nbsp;km
|align="right"|29 June 1920
|align="right"|31 July 1924
|align="right"|&mdash;
|align="right"|&mdash;
|-
|Closure of the [[Zuyderzee]]
|align="center"|[[Afsluitdijk]]
|align="center"|32&nbsp;km
|align="right"|January 1927
|align="right"|23 May 1932
|align="right"|&mdash;
|align="right"|&mdash;
|-
|[[Pilot Polder Andijk]]
|align="center"|-
|align="center"|1.9&nbsp;km
|align="right"|1926
|align="right"|Early 1927
|align="right"|40 ha
|align="right"|27 August 1927
|-
|[[Wieringermeer]] Polder
|align="center"|-
|align="center"|18&nbsp;km
|align="right"|1927
|align="right"|27 July 1929
|align="right"|20,000 ha
|align="right"|31 August 1930
|-
|[[Noordoostpolder]]
|align="center"|-
|align="center"|55&nbsp;km
|align="right"|1936
|align="right"|13 December 1940
|align="right"|48,000 ha
|align="right"|9 September 1942
|-
|[[Flevoland|Eastern Flevoland]] Polder
|align="center"|-
|align="center"|90&nbsp;km
|align="right"|Early 1950
|align="right"|13 September 1956
|align="right"|54,000 ha
|align="right"|29 June 1957
|-
|[[Flevoland|Southern Flevoland]] Polder
|align="center"|-
|align="center"|70&nbsp;km
|align="right"|Early 1959
|align="right"|25 October 1967
|align="right"|43,000 ha
|align="right"|29 May 1968
|-
|[[Marker Wadden]] Polder
|align="center"|[[Houtribdijk]]
|align="center"|28&nbsp;km
|align="right"|Late 2012
|align="left"|The project is still under construction as of 2021.
The first island was completed in late 2020.{{Update inline|date=January 2025}}
|align="right"|2,500 ha
|align="right"|24 September 2016
|}