The construction

New Inventions and Techniques

Afsluitdijk photographed in the direction of Wieringen
Building a dam like the Afsluitdijk had never been attempted before, so there was no previous experience to rely on. Building the Afsluitdijk therefore involved the discovery of a number of new inventions and techniques. After building the dam in the Amsteldiep in 1920, the “Rijks Geologische Dienst” (National department of Geology) made a new discovery - boulder clay. Boulder clay is a solid and tough material that came from Scandinavia during the second last ice age. Boulder clay holds its position through rates of flow up to 4 metres per second, so the material was suitable for the draining of the Zuyder Zee. The boulder clay was extracted from the bottom of the sea using a dredging machine, which in those days was a relatively new technique.


The first section of the Afsluitdijk was a 2.5 kilometre wide boulder clay dike, built in the Amsteldiep. This way, the island of Wieringen was connected to the mainland. A ringdike was built around the Wieringermeer, and the polder was pumped dry using the pumping-engines near Medemblik and Den Oever. By 1930, it was completely impoldered.
Meanwhile, in 1927, the construction of the Afsluitdijk began. Osier mats with dumpstones were used to fortify the two future closing breaches. After that, the dike was built up out of boulder clay, sand, and stones. In March 1931, construction workers suffered a large setback - divers discovered that the osier mats were riddled with woodworm: a worm or insect larva that bores into wood. Moreover, seawater had heavily corroded the galvanized steel wire that was holding the sink pieces together. To prevent the dam from washing away, the material had to be replaced as soon as possible. Barite, a mineral that had to be imported from Germany, was chosen as the new material. The barite was a success and the damn was saved.