ultramarin marine translations
ultramarin.online
nl kolk   put op de rivierbodem en langs de oever veroorzaakt door stroming of uitwassing; 
de Kolk schroffe Austiefung in der Flußsohle längs des Ufers;
en scour
pond (under water)
a depression in the bottom of the river along the bank caused by wash and/or current;
fr affouillement