Dynamic beach ridge management on the Wadden Islands
Dynamic beach ridge management means leaving nature to develop naturally as long as there is no negative effect for safety. Coastal managers have been applying this method on the Frisian Wadden Islands since 1990. Sand nourishments keep the base coastline in place as it was in 1990. But by allowing erosion and growth to take place where no base coastline has been established increases the value of nature and even contributes to safety in the long run. Because the beach ridge is not the primary dam protecting the towns, wind-blown openings or drifting sand blown over the top are not a threat.
There are many advantages to dynamic management. There is more room for water during storms, inland dunes can grow taller from the drift sand so that they are more resistant to sea-level rise and fresh minerals reach inland dune flora where they otherwise slowly leach away.
The residents on the islands react diferently to dynamic beach ridge management. For some, it is unaccebtable. For others, thanks to good communication, there is little resistance. It is now a matter of getting used to a philosophy that erosion is not always a threat. There is even added economic value when the islanders realize that a dynamic and variable coast is attractive to tourists.
- A notch in the beach ridges
- Notch in the beach ridge, Ecomare
By holding down drifting sand with reed screens and marram grass, the beach ridge in many places along the coast resembles a straight wind-blown dike, lacking peaks and valleys. This has not always been the case. In old paintings, one can see that the original beach ridges had many drift-hollows and notches. A few dune valleys flooded regularly with water during extremely high tides. In this way, characteristic brackish water environments were created where unique plants and animals could be found. This scene has more or less disappeared from the Dutch dune environment today. However where it is safe, there are plans to re-establish notches in the beach ridges. Some examples are the notch in the beach ridge between Bergen and Schoorl and the nature area the 'Strandvlakte' on Schiermonnikoog.
- Reed and branch windscreens
- Placement of branch screens, Ecomare
Reed windscreens are placed on the seaside foot of the dunes. The windscreens catch drifting sand, which is blown from the beach in the direction of the dunes. In addition, reed windscreens can also hold sand down on the dunes. Twigs, braided together, are also used. Maintenance of windscreens costs a lot of time and effort. Therefore marram grass is planted as soon as the sand hill is high enough to form a freshwater bell.
- Planting marram grass
- Planting marram grass along the seaside, Ecomare
Marram grass slows down the wind so that the blown sand falls behind the bundles of grass. It easily survives the silty drift-sand and the sea wind, which is why one plants marram grass in places where the dunes need to be re-enforced. Marram grass continues to grow in the nutritious drift-sand so that the beach ridges are held in place and continue to grow higher.
- Dune foot defences
- Dune foot defences, Ecomare
Dune foot defences are dike works placed parallel to and at the foot of the dunes. They are often less steep than the dune first was. These defences provide more protection to the natural dune during high water levels. Sometimes these structures eventually disappear under drifting sand and are overgrown with plants.
- Shoving dunes inland
- Dunes being shoved inland, Ecomare
Between 1970 and 1990, when the beach ridges threatened to collapse, the outer row of dunes was shoved into the dune valley lying behind with the help of bulldozers. A huge massive body of sand was created in that way. This method was effective when it came to defending the land from the sea, however dune valleys were completely destroyed. Many protests erupted, as argument that the dune valleys and the transition between young and old dunes are extraordinary nature areas. From the view point of nature conservation, this method is no longer applied, also made possible when sand nourishments turned into a successful and less damaging method for protecting the beach ridges.
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