Grevelingen dam

Grevelingendam (1958-1965)

In 1958, a then revolutionary technique is chosen to build part of the six kilometer long Grevelingendam, which connects Schouwen-Duiveland to Goeree-Overflakkee. Large concrete blocks are dumped into the water by using cable cars, until a framework of concrete blocks is created.  For the remainder of the dam, familiar techniques such as rainbowing sand and sinking caissons are used.

The cable car system is developed by Rijkswaterstaat in cooperation with the French company Neyrpic. On the coast of Goeree-Overflakkee a loading dock is built and in the middle of the gap to be closed off, a pillar is erected as a support point. On the Oude Tonge sandbank – an existing sandbank especially raised for that purpose – a loading and  storage area for sand, cement, stones and rock is created. In total, 195 million kilos of bulk materials are situated there – comparable to the combined weight of 39.000 Asian elephants.

Grevelingendam
Grevelingendam

Gondolas

The bulk materials are transported in a net under a gondola. Hanging on 92 millimeter thick steel cables, 10 gondolas move back and forth continuously, carrying 10.000 kilos of stones each. The gondolas have their own motor and driver and take 20 minutes to travel from the loading dock to the area where the stones are dumped.

This method is not cheap. All the bulk materials must be imported. In order to keep the costs down, sand from the Oude Tonge sandbank is used in addition to the bulk materials. The sand is mixed with water to form a thick sludge which is then injected into large bags. Large lumps of tarmac are also used as building material.

Measurements

During construction, measurements are taken from time to time to see if everything goes according to plan. The water currents are closely monitored. If the flow velocities become too high, the stone deposits can start to slide and that is to be prevented.

The cable car method is used for the northern part of the dam: a channel of one kilometer in length. The much narrower southern channel at Schouwen-Duiveland is closed with custom-made caissons. An eleven-meter-wide bridge and a lock of 125 meters long and 16 meters wide complete the Grevelingendam.

What makes Grevelingendam special is the fact that it is not primarily intended to protect against flooding. The dam ensures that water from the Grevelingen cannot flow back to the sea via Haringvliet or Oosterschelde. Eliminating these extra currents facilitates the construction of the Haringvliet dam and then the Brouwersdam and the storm surge barrier in the Oosterschelde.