@Walter Hinteler,
Only when people learnt to write (and archive) after the 'dark age', we've got more evidence about the great floods in and around the German Bight:
- the Julian's Flood on the 17th of February 1164,
- the First Marcellus Flood on January 16, 1219,
- the Second Marcellus Flood, January 15/16, 1392.
The latter - aka
(First) Grote Mandreke - destroyed some dozens of towns and villages, killing ten thousands (according to local chronics more than 100.000, which seems an exaggeration though).
Most famous and in the news NOW (reason: see my above post
) is the (mostly sunken) island of Nordstrand and the large (sunken) town Rungholt
(Cutout from the map of Johannes Bleau, 1662:
Ducatus Sleswicum sive Iutia Australis)