In the case of a Wadden Sea, the ground has only a slight gradient, with the difference in height generally being less than one meter over a length of one kilometer. At the same time, the difference in water level between high water and low water is at least two meters so that a sufficiently large area falls dry.
In the area of river mouths, fine-grained material and suspended matter, which were previously washed from the land into the rivers in flat areas with relatively high levels of precipitation, are carried into the sea by the currents. Land-based winds also feed this material into the Wadden Sea, which then becomes part of the tidal sediment.
The Wadden Sea is divided into three zones. The sublittoral area lies below the mean low water level, which also includes the tidal creeks. The supralitoral area lies above the mean high water level and is only flooded when the tides are particularly high. If there is no human cultivation, salt marshes are usually created here. The actual watt, i.e. In other words, the areas that are below the water level at high tide and above the water level at low tide are the eulittoral area. Offshore islands and sandbanks often form a protection against the surf of the open sea and slow down the seaward ebb current.