The Slaperdijk from Spaarndam to Santpoort

The Slaperdijk is located north of Haarlem between Spaarndam and Santpoort. As a child I lived in Haarlem-Noord and regularly cycled along this dike to go fishing in Spaarndam. I never realized then what a special function this dike has had through the centuries.

Cow at the Slaperdijk.

Cow at the Slaperdijk.

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In November 2021 I saw a booklet by Frederik Willem Conrad Sr. in the Archives of the Principal Water Authority of Rijnland, which described in detail how the Slaperdijk functioned and how often it was flooded. For me this was very interesting, especially since I knew the area so well from my youth and had no idea of its interesting history.

At the time the dike was constructed, the sea inlet IJ was in open connection with the Zuiderzee and the areas around the IJ were regularly flooded. The Spaarndammer dike played an important role since the beginning of the fourteenth century in protecting the area south of it against these floods.

Initially, the Slaperdijk between Spaarndam and Santpoort did not yet exist, because the Velserbroek Polder was located in front of it. When parts of the Rijnland area were flooded by regular breaches of the Velserbroek Polder dike from the IJ, a start was made in 1612 with the construction of the Slaperdijk to hold back the floodwater in the event of dike breaches of the Velserbroek Polder dikes, and in this way to protect the area of Rijnland against this.

Because Amsterdam objected, there were lengthy discussions about the height that the Slaperdijk could have. Eventually, in 1660, it was agreed that this dike could not be higher than 1.36 metres +MSL (mean sea level) (52 Rijnland inches), which meant that it was then approximately 95 centimetres (three feet) lower than the sea dikes and sluices at Amsterdam. Measurements in the nineteenth century by Conrad showed that the Slaperdijk was then approximately 1.43 metres lower than the Spaarndammer dike and approximately 1.78 metres lower than the IJdijk.

During the eighteenth century, data are available for eighty-two years. The period 1750 to 1767 is missing. In the eighty-two years, the Slaperdijk was sixty times flooded from the IJ, which was still very regular.

Rijnland suffered a lot of damage from these floods. On the one hand, this was due to the extra burden on the Collecting and transport system of Rijnland and the associated problems with flooding of polders bordering the Slaperdijk and of parts of Haarlem, as well as the necessity to stop the drainage of the polders in the south of Rijnland, for which a level to stop pumping existed. This meant that these polders had to stop their discharge if the water in the Collecting and transport system of Rijnland rose too high. In addition, the floods often involved brackish water, due to the mixing of fresh water discharged to the IJ and salt water from the former Zuiderzee. At that time, however, Amsterdam was more powerful than the Principal Water Authority of Rijnland and so it went as Amsterdam wanted.

In 1863, the Amsterdam Canal Company was granted a concession to construct the North Sea Canal, which also included the realisation of the IJpolders on both sides of the IJ. As part of the work, the Oranje sluices were completed in 1872, which closed off the IJ from the Zuiderzee and gave it a fixed water level. As a result, the Slaperdijk ceased to function after 260 years.

The Slaperdijk is still clearly present in the landscape for by far the largest part. It is clear that the dike no longer has a function, because in some places it is now intersected at road intersections. Few of those who drive along or over it will realize what an important function this dike had before the construction of the North Sea Canal, by on the one hand protecting the area of Rijnland against flooding from the IJ, but on the other hand allowing limited flooding when an extremely high water level occurred. In this way, flooding of Amsterdam was at least reduced, or even completely prevented.

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