The Zeeland Delta

Almost every Dutch sea dive happens inside a landscape that was deliberately rebuilt after a single night.

On 1 February 1953 a spring tide met a north-westerly gale and the sea came over the dykes of Zeeland, South Holland and North Brabant. The flood killed 1 836 people. Within three weeks the government had appointed a Delta Commission, and the plan it produced — the Deltaplan — set out to shorten the Dutch coastline by damming the sea arms of the Rhine–Meuse–Scheldt delta. Work ran from 1954 to 1997 and cost 8.2 billion guilders. It also, incidentally, created most of the Dutch sea dive sites.

The commission did something quietly radical on the way: it put a price on a human life (about €2.2 million in 2008 money) and used it to calculate how much protection each region could justify. North and South Holland were to be safe against the storm that comes once in ten thousand years. That calculation is still the basis of Dutch flood law.

The Grevelingen

The Grevelingendam closed the eastern end in 1965 and the Brouwersdam closed the western end in 1971, and between them they left a 14 000-hectare body of water with no tide and no river. It is the largest saltwater lake in Europe. Cut off, it began to go brackish on rainwater and polder drainage, so in 1978 a sluice was cut through the Brouwersdam to let the North Sea back in on a controlled basis.

For divers the result is unusual: sea water, sea life, and no current worth the name. Visibility is often better than the Oosterschelde because nothing stirs the bottom. The price is oxygen — with no tide to mix the column, the deep parts of the lake go anoxic in late summer and the life there dies back each year. Restoring a real tidal exchange through the Brouwersdam has been under discussion for two decades.

Sites here: Koepeltje, Dreischor Gemaal, Dreischor Loswal, Dreischor Langeweg, Den Osse haven, Scharendijke, Scharendijke Kabbelaar, Bommenede.

The Oosterschelde

The Oosterschelde was supposed to be dammed too. It was not, and that is the most interesting thing about it. Fishermen who worked the oyster and mussel beds and a young environmental movement fought the closure through the 1970s, and in 1976 the government changed the design: instead of a dam, a storm surge barrier with 62 steel gates that stand open and are only dropped when a surge is forecast. The Oosterscheldekering opened in 1986. The estuary stayed salt, and stayed tidal.

It did not stay the same. The barrier's piers narrow the mouth, so less water moves in and out on each tide — the range dropped from roughly 3.4 m to 3.0 m and the currents weakened with it. The tidal flats are no longer fed enough sand to rebuild what the waves take, a problem the Dutch call zandhonger, sand hunger; the shoals are slowly flattening and the Rijkswaterstaat now periodically dumps sand to hold them. What divers get in exchange is a sheltered salt estuary with sharp tidal windows: you dive the slack, and the tables on the dyke tell you when it is.

Sites here: Zeelandbrug, Kerkepad, Zijpe, Zoetersbout, De Stelhoeve, Tetjes, Plaat Oude Tonge, Plompe Toren, Silveren Schor, Anna Jacoba.

Sources

• Wikipedia, Delta Works — https://en.wikipedia.org/wiki/Delta_Works
• Wikipedia, Grevelingenmeer — https://en.wikipedia.org/wiki/Grevelingenmeer