The three-part-dam

Diagram of the closure of the channels of current
Current channels diagram
The section of the dam can be divided into three completely separate parts. From north to south: 1) a wide and shallow part, 2) a part at the Amsterdam ordnance zero, the Island of Oude Tonge, and 3) a narrow and deep part. A different technique was used for each part. The Island of Oude Tonge would first be raised using sand from the seabed. After that, the narrow, deep southern part would be closed by caissons. Finally, the wide and shallow northern part would be closed by a cable way and plunging blocks. To complete the whole, a bridge and lock would be built.

Raising the Island of Oude Tonge

Plug with concrete blocks.
Plug
In 1957, four years after the flood disaster of 1953, the Island of Oude Tonge was raised. A large sand bank was formed so that it could be used as the starting point of the Grevelingen dam. Long tubes connected to sand pumps in the North Sea transported sand to the Island. The raised sand bar divided the Grevelingen into two currents even more distinctively.

The closure of the northern part

The filling of the caissons with sand
Filling caissons
On the side of Schouwen-Duiveland, the canal was only 600 metres wide, but twenty metres deep. The current was much stronger than on the north side, where the closing gap was greater than one kilometre. While the Island of Oude Tonge was raised, the southern canal (at Schouwen-Duiveland) was also filled with sand, to reduce the depth to a maximum of five metres. Next, the caissons which were made to size, were placed into the canal.

The closure of the southern part

Deposit of stones from a 1000 kg bag. At the right a carrying post can be seen.
Deposit of stones
After the 600 metres from Schouwen-Duiveland towards the Island of Oude Tonge were bridged, a gap of one kilometre remained. Instead of caissons, a new method was used to seal this part. A cable way was used to plunge large boulders. Cradles were hung on the cable way, to which silos and nets were connected. The nets were loaded with sand, cement, concrete, and boulders. These were then plunged into the water along certain sections. The problem was that the closing gap was so wide at certain places, that caissons were unable to be used.