Safety and Recovery

How could the flood of 1953 happen?

Long before 1953, experts are concerned about the dikes in the south-west of the Netherlands.

In the 1930s, Rijkswaterstaat (the Ministry of Infrastructure and Water Management) calls for something to be done urgently. A think tank carries out research into the consequences of the reclamation of the Hollandse Biesbosch. The conclusion is clear and alarming for Dordrecht and the surrounding areas: the dikes are too low. Previous reports already showed that the dikes in West Brabant do not meet safety requirements.

More than enough reason to raise the alarm, but the call of the experts is barely heard. Engineer Robert de Muralt invents an inexpensive way to raise the dikes: 120 kilometers of dikes bordering the sea are provided with a ‘Muralt wall’ on top, but that’s it. In many places in April 1943 the water runs over the top of the dikes during a period of exceptionally high water levels. Research is being done again and once again the results are alarming.

WWII

The outbreak of the Second World War prevents the plans of Rijkswaterstaat to improve the dikes around Dordrecht from being carried out. However, further studies are completed during WW II and a Storm Flood Commission is drawn up. However, Rijkswaterstaat prefers to focus its attention on land reclamation in the Zuiderzee at that time.

During the Second World War, the Zeeland countryside suffers a lot of damage due to bombing. Parts of Zeeland are also deliberately flooded. Restoration work on the Zeeland landscape starts in March 1945 and in February 1946 the dikes around Walcheren are closed again. The much needed raising of the dikes, according to Rijkswaterstaat,  does not happen, despite the insistence of Rijkswaterstaat’s think tank.

Salinisation

The salt levels in the agricultural soil are also becoming a problem. Due to the deepening of waterways on the coast, the salty water can increasingly flow inland and that is not without consequences for arable farming. Many agricultural crops cannot withstand salt or brackish water and die. Plans are being made to counteract salinisation.

There have been no serious floods for years and the available money is desperately needed to ensure that arable farming can keep its head above water and harvests no longer fail. Restoring the damage from the war to the countryside also takes up a great deal of time and money and this all diverts attention from the condition of the dikes.

Weerkaart KNMI 31 januari Watersnoodramp
Weerkaart KNMI 31 augustus Watersnoodramp

Hurricane

In addition to the poor condition of the dikes, an unfortunate combination of climate conditions in the south-west of the Netherlands is the problem in 1953. A depression south of Iceland develops into a hurricane near Scotland and moves to the Netherlands.

In the evening of January 31, 1953 wind force 11 is measured. Due to the force of the storm the water is pushed up by more than 3 meters and on top of that it is also spring tide. That turns out to be fatal for the badly maintained dikes. That night, 89 dikes collapse.

The flood disaster makes it clear that something has to be done about the dikes now. On 4 February 1953, then Prime Minister Willem Drees announces in Parliament that restoring the dikes will receive the highest priority. The Delta Committee is founded, led by civil engineer A.G. Maris, then Director General of Rijkswaterstaat. Volunteers and dike workers are already busy closing the holes in the dikes so that the sea has no longer free rein and the permanent repairs can begin.

Dijkgat Watersnoodramp
Dijkgat

Stone, mats and cofferdams

The flood disaster has resulted in various sized holes in the dikes in about five hundred places. Repairing them is started immediately. During the disaster night and the following days, breaches are closed with sandbags. Those ’emergency plugs’ are reinforced during the following weeks with stone, mats, cofferdams and ships.The start of this definitive repair work is difficult. The different organisations involved each have their own idea about what the best method is. One wants to work with caissons (huge concrete boxes) and the others prefer clay and stone. Eventually, caissons are chosen.

Sluiting Ouwerkerk Caissons
Plaatsing van de caissons bij Ouwerkerk

Caissons

At the beginning of April most of the disaster area is reclaimed, but there are some hard-to-close holes, such as at Bath, Kruiningen, Schelphoek and Ouwerkerk. The hole at Bath is closed with the hull of a ship. At Kruiningen three holes need to be closed: the western hole, the eastern hole and the hole in the ferry port. Closing the eastern hole turns out to be a difficult task. Eventually the job is done with a ring dike (for which 40 caissons are used) and a 33 meter long pontoon of so-called ‘unit caissons’.The last gap to be closed is the one at Ouwerkerk. The flow velocities are so high that initially it is not possible to maneuver the heavy caissons in exactly the right position, but finally the hole is closed on 24 November 1953. For the dike workers it feels like a victory now that the disaster area can be officially declared dry.

How does a caisson work