More than one-quarter of the Netherlands is below sea level. The coastline along the North Sea (approx. ) is protected against flooding by natural sand dunes (only in the estuaries and behind the barrier islands there are no dunes). This coastline is eroding for centuries; in the 19th and beginning of 20th centuries it was tried to stop erosion by construction of groynes, which was costly and not very successful. Beach nourishment was more successful, but there were questions on the method of funding.
