Editing Afsluitdijk (section)

=== Building the dyke ===
[[Wieringen]] was connected to the mainland with the short [[Amsteldiepdijk]] in 1925; the ''{{lang|nl|Afsluitdijk}}'' would be {{convert|20|mile|km|order=flip}} in length. The inland side is heavy stone; the seaward side is [[boulder clay]] with [[Melaleuca uncinata|brushwood]] [[gabion|mattresses]] above, weighed down by [[basalt]] boulders and old concrete.<ref name="ley196110">{{Cite magazine |last=Ley |first=Willy |date=October 1961 |title=The Home-Made Land |department=For Your Information |url=https://archive.org/stream/Galaxy_v19n06_1961-08#page/n65/mode/1up |magazine=Galaxy Science Fiction |pages=92–106 }}</ref> Previous experience had shown that boulder clay was superior to just sand or clay for a structure like the Afsluitdijk, with the added benefit that [[till]] was in plentiful supply in the area; it could be retrieved in large quantities by simply [[dredging]] it from the bottom of the Zuiderzee. Work started at four points: on both sides of the mainland and on two specially made construction-islands ([[Kornwerderzand]] and [[Breezanddijk]]) along the line of the future [[Levee|dyke]].

From these points, the dyke slowly grew by ships depositing till into the open sea until it breached the surface. The nascent dyke was then strengthened from land by basalt rocks and mats of [[Willow#Environment|willow switch]] at its base. The dyke could then be finished off by raising it further with sand and finally clay for the surface of the dyke, on which grass was planted.

As the dyke grew, physicist [[Hendrik Antoon Lorentz]] calculated the force of the tide as the smaller gap made it stronger. Ten thousand workers, 27 large dredges, 13 floating cranes, 132 barges, and 88 tugs worked on the project at the end, timed to close the dyke at low tide; it was finished on 28 May 1932.{{r|ley196110}} Construction progressed better than expected; at three points along the line of the dyke there were deeper underwater trenches where the tidal current was much stronger than elsewhere. These had been considered to be major obstacles to completing the dyke, but all of them proved to be relatively straightforward. Two years earlier than initially thought, the Zuiderzee ceased to be, as the last tidal trench, the ''Vlieter'', was closed by a final bucket of till. The IJsselmeer was born, even though it was still salty at the time.

The dyke itself however was not finished as it still needed to be brought up to its required height and a road linking Friesland and North Holland (the current [[A7 motorway (Netherlands)|A7]]/[[European route E22|E22]] [[motorway]]) also remained to be built. On 25 September 1933, the Afsluitdijk was officially opened, with a monument designed by architect [[Willem Marinus Dudok]] marking the spot where the dyke had been closed. The amount of material used is estimated at {{convert|23|e6m3|e6cuft|abbr=unit}} of sand and {{convert|13.5|e6m3|e6cuft|abbr=unit}} of till and over the years an average of around four to five thousand workers were involved with the construction every day, relieving some of the unemployment following the [[Great Depression]].

Besides the dyke itself, there was also the necessary construction of two complexes of shipping [[canal lock|locks]] and discharge [[sluice]]s at both ends of the dyke. The complex at Den Oever includes the ''Stevin'' lock (named after the son of [[mathematician]] and [[engineer]] [[Simon Stevin]], Hendrik Stevin, who was the first making a plan to close the Zuiderzee in 1667<ref>{{Cite book |title=Wisconstich filosofisch bedryf |last=Stevin|first=Hendrik|url=https://books.google.com/books?id=rm0_AAAAcAAJ|publisher=Philips de Cro, Leiden|date=1667|language=nl|trans-title=mathematical and philosofical transactions}}</ref>) 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 (named after the physicist) and two series of five sluices, making a total of 25 discharge sluices. It is necessary to routinely discharge water from the lake since it is continually fed by rivers and streams (most notably the [[IJssel]] river that gives its name to the lake) and [[polders]] draining their water into the IJsselmeer.