Brouwers dam

Brouwersdam (1962-1971)

Due to the construction of the Brouwersdam – on the east side the Grevelingen is closed off already by the Grevelingendam – lake Grevelingenmeer  is created. Building the Brouwersdam is a good exercise for the construction of the even more complex Oosterscheldekering. The ‘gap’ to close between Schouwen-Duiveland and Goeree-Overflakkee is 6.5 kilometers long and to fill it both caissons and a cable car are used.

The Brouwersdam runs from Schouwen-Duiveland to consecutively the sandbanks Middelplaat and Kabbelaarsplaat and from there to Goeree-Overflakkee. Because the water passage between the two sandbanks is very narrow and shallow, it is decided to make one sandbank from both sandbanks. Two openings now remain: a northern and a southern one.

Caissons are used to close the northern gap – from the Kabbelaarsplaat to Goeree. Twelve caissons, each 68 meters long, 18 meters wide and more than 16 meters high, are built, plus two ‘abutment caissons’. All caissons have 12 openings of 5 meters wide each. During the closure the water flows through them.

Sand and stone

Once all the caissons are in exactly the right place, they are submerged. During slack tide – when the current is minimal – the openings in the caissons are closed by sliders, after which the hollow concrete sections are filled with sand and stone. The northern section is closed.

In order to close the southern part – from the Middelplaat to Schouwen, large concrete blocks are dumped  into the water from gondolas on the cable cars, until a basic dam of concrete blocks is created. In this southern section, 240.000 concrete blocks of 2.5 tons each are used. The spaces between the concrete blocks are filled with sand so that water can no longer flow through.

Closing off the Grevelingen completely means that the water in the Grevelingenmeer is at a complete standstill from one day to the next. The disappearance of the tides has far-reaching consequences for the ecosystem. Small shellfish die within a few days and plants that depend on salt water also wilt away. Within a few weeks after the closure, rotting plants and animals are floating everywhere.

Brouwersdam
Brouwersdam

Grass and grain

Mud flats -clay soil areas on the outside of the dikes – are drying out. To prevent further drying out and soil erosion, grasses and grains are sown. In addition, screens are made from branches. Dunes slowly form around these screens. The oystercatchers have already left the area. In return,  pied avocets, Kentish plovers, common ringed plovers and little terns move in. They use the area, which is full of shells, as a breeding ground.

Later – when more plants grow on the former mud flat – the bird population changes again. Now there are lapwings, redshanks, godwits and larks. The Hompelvoet – an island in the Grevelingen – turns into the largest breeding ground for Sandwich terns in the delta area, giving home to 3000 breeding pairs.

Sluice

To prevent the desalination of the Grevelingenmeer, a sluice was built into the dam in 1978. The opening consists of two concrete tubes of 195 meters each and an equally long fish passageway. Plaice can now swim unhindered from the Grevelingenmeer to the North Sea. The oyster, which appeared to have become extinct in the lake, returns.