Grundsee
The basic sea is water waves in heavy seas , which in the relatively flat coastal waters become higher and thus steeper before they break . The reason for this is that waves propagate more slowly in shallower water than in deep water. Compared to deep water, they can be twice as high there. Ground lakes arise where the water depth is less than half the wave length or about five times the wave height on the surface of the water. Grundseen got their name because they stir up the seabed and therefore the water there carries with it larger amounts of suspended load , especially relatively coarse particles ( sand ) (see also → Tempestit ).
Ground lakes are dangerous because ships can cross, overturn and sink in the very steep, breaking sea. Furthermore, it can also happen that ships hit the bottom when the water depth between two wave crests is less than the depth of the ship. From this danger are also rescue boats affected if in storms in coastal areas or near shoals rescue operations continue (see also: unhappiness the lifeboat Alfried Krupp from 1 January 1995 or Adolph Bermpohl 1967).