Dyke builders generally take into account a time horizon of several decades to a century. If the sea level rise is not too bad, the dikes will keep the Netherlands dry for the next century.
But if the sea level rise – a consequence of global warming and melting polar ice – strong progress, then dikes alone will not suffice. One idea is to open up areas of land to water and nature, so that sand, silt and peat can contribute to ‘land level rise’. The sooner we start doing this, the more we will benefit from it in the future. According to Weisscher de Biesbosch, this is the prime example that this can be achieved.
Biesbosch has risen 2 meters
The Biesbosch was created 600 years ago after the Saint Elizabeth flood. At that time, the responsibility for maintaining dikes was still very fragmented because it rested with individual farmers. These were times of financial turmoil, with the result that dikes were less well maintained. After the first breakthrough of the seawater in the Grote Waard near Dordrecht, there was no stopping it. Farmers and residents withdrew and nature was given free rein. The area was watered down and rivers started to deposit silt. People went fishing there, planted pilot whales and slowly but surely a process of mooring started. As a result, the Biesbosch has become two meters higher than surrounding polders that were not affected, simply by washing up sand and silt, and plant and tree growth. In the landscape this is just hard to see.
“We feel very safe in the Netherlands,” says Weisscher, “but the later we start with land-level rise, the greater the chance that cities will be flooded.”
In Zeeland, for example, cut through the dikes in a controlled manner, so that the land behind can rise with the sea level due to sand supply and tidal action.
Regulated land level rise
According to Weisscher, by creating wider barriers between the water (sea and rivers) and the land and by (temporarily) breaching dykes, the process of land-level rise can be set in motion in a controlled manner. In the laboratory he built a ‘sandbox’ in which he can mimic the process of silt deposition and plant growth. Using a computer model of the Western Scheldt, he calculates how things could go and in the Zeeland Hedwigepolder – which has been flooded again after years of struggle – fellow researchers are testing out how things are going in reality.
Don’t forget that the Netherlands used to be much bigger, says Weisscher. The IJsselmeer? Wadden Sea? peatland. Zeeland was a largely mature landscape and through peat extraction a lot of land was indirectly lost there (as a result of several ‘sea intrusions’), which we have only partially reclaimed with polders. Reduce the pumping of groundwater from the Green Heart, so that larger freshwater lenses can form underground. For example, in Zeeland, cut through the dikes in a controlled manner, so that the land behind can rise with the sea level due to sand supply and tidal action. That will really limit the damage in the event of any future breakthroughs. Because although dikes and other techniques can keep us dry, the chance of a flood never becomes zero. We can also enjoy these new wetlands, because this landscape can possibly be combined with wet agriculture and recreation.
According to Weisscher, the biggest obstacle is not technology or nature, but the question of how to gain public support for the idea of land-level rise. Do we dare to make the switch from ‘losing land’ to ‘investing in land for the future’?
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Rethink: let the land level rise – ‘Embrace the rising water, don’t arm yourself against it’ – Foodlog