When the dikes were built along the North Sea coast in the 12th century, adequate drainage of the diked land also had to be ensured. The sluices were “invented” - i.e. culvert structures in the dike for the natural drainage of the hinterland, which at the same time should be protected from floods or floods and the ingress of salty sea water. Sluices have closure devices that close automatically due to the pressure of the water when the outer water of the North Sea rises higher than the inland water level during high tide. And they open automatically when the outside water falls below the inside water level at low tide.
Initially, folding shacks were used on the East Frisian North Sea coast, with wooden flaps suspended at the top and suspended in the water. From the 15th century onwards, larger gates with two wooden wings hung on the sides became popular. Storm gates were installed in or behind the culvert - these were closed by hand in an emergency.