Hoorn, Enkhuizen & Medemblik

 

 

 

Medemblik obtained town walls in 1572, so that the castle lost its roll as a refuge for the citizens, which led to its partially dismantling in 1578. Over the centuries the castle fell into decay, but in 1889 it became property of the crown and was restored to be used as a courthouse, which function it served until 1934. Anticipating the German invasion, the Rijksmuseum in September 1939 chose the castle as the initial hiding place of Rembrandt's Night Watch. 

 

IJsselmeer, Lake IJsel, alternative spelling: Lake Yssel) is a shallow artificial lake of 1100 km² in the central Netherlands bordering the provinces of Flevoland, North Holland and Friesland, with an average depth of 5 to 6 m. The IJsselmeer is the largest lake in Western Europe. The IJsselmeer is a freshwater lake fed through the Ketelmeer by the river IJssel, which gives it its name. It is mainly fed by water from the Rhine since the IJssel is a branch of it.

 

The IJsselmeer was created in 1932 when an inland sea, the South Sea, was closed by a 32 km dam, the Afsluitdijk. This was part of a major hydraulic engineering project known as the Zuiderzee Works, that years later led to the reclaiming of land from the IJsselmeer, thereby diminishing the size of the lake.

The Afsluitdijk (Frisian: Ofslútdyk; English: Enclosure Dam) is a major causeway in the Netherlands, constructed between 1927 and 1933 and running from Den Oever on Wieringen in North Holland province, to the village of Zurich in Friesland province, over a length of 32 kilometres (20 mi) and a width of 90 m, at an initial height of 7.25 m above sea-level. It is a fundamental part of the larger Zuiderzee Works, damming off the Zuiderzee, a salt water inlet of the North Sea, and turning it into the fresh water lake of the IJsselmeer. 

 

Previous experiences had demonstrated that boulder clay, rather than just sand or clay, was the best primary material 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 dike.

 

From these points, the dike slowly grew by ships depositing till into the open sea in two parallel lines. Sand was then poured in between the two dikes and as it emerged above the surface was then covered by another layer of till. The nascent dike was then strengthened from land by basalt rocks and mats of willow switch at its base. The dike could then be finished off by raising it further with sand and finally clay for the surface of the dike, on which grass was planted. Construction progressed better than expected; at three points along the line of the dike 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 dike, but all of them proved to be relatively straightforward. On 28 May 1932, 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 dike itself however was not finished yet as it still needed to be brought up to its required height and a road linking Friesland and North Holland also remained to be built. On 25 September 1933, the Afsluitdijk was officially opened, with a monument designed by architect Dudok marking the spot where the dike had been closed.

 

 

Beside the dike itself there was also the necessary construction of two complexes of shipping locks and discharge sluices at both ends of the dike. The complex at Den Oever includes the Stevin lock (named after Hendrik Stevin, a son of mathematician and engineer Simon Stevin) 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 Hendrik Lorentz, the famous physicist, who personally did the calculations of the tides that were crucial to the construction of the Afsluitdijk) 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.