Inlayers and wet fields
In order to prevent a large stretch of hinterland from flooding in the event of a dike breakthrough, or in the event of a sudden dike subsidence or river erosion, inlayer dikes have been constructed as spare dykes in dangerous places behind the sea dike. The area between the original sea dike and the spare dike is called an inlayer. Originally these were fields or meadows; nowadays these deep wet marshes are valuable natural areas.
These inlayers are very important for birds. Many of these inlayers contain breeding colonies of, for example, black-headed gulls and terns. Birds that breed elsewhere can also often be found here. When water levels are low they feed themselves outside the dikes on silts and plates. To get the right tide, they fly to the inlayers when the tide is high where they wait for low tide in a large group.
The soil used to make the dikes was excavated from the inlayer itself or from the immediate surroundings. These fields can now still be recognized by their long strips of soil alternated with long dug strips.