Ghyben Herzberg lens
The Ghyben-Herzberg lens (ger .: freshwater lens , Ghyben-Herzberg lens ) also easy freshwater lens called an underground is fresh water found on the sea islands. The prerequisites for their formation are a humid climate and a groundwater-conducting subsurface.
On smaller islands there is usually a body of groundwater made up of salt water . However, since there is only very little mixing of the water body in the soil ( laminar flow through the porous bodies in the soil), the water seeping into the subsoil can collect on the surface of this salt water table and form a watch-glass arched groundwater body of fresh water. This formation is facilitated by the fact that the density of fresh water is slightly lower than that of salt water.
To the side and in the depths of this body, in the transition to salt water, there is usually a brackish water zone of varying strength. The fresh water of this lens results solely from precipitation .
These fresh water resources are the source of drinking and industrial water on most islands. Exceptions are rock islands in which no groundwater body exists. When using the freshwater lens to withdraw water, only as much water may be withdrawn as regularly re-forms. Larger withdrawals must be distributed over the lens, as a one-sided strong withdrawal can lead to the freshwater lens being used up in the corresponding area and brackish or even salt water being sucked in as a result ( salt water intrusion ). Also, the well systems must not be sunk to the salt water level, as mixed water is then pumped.
See also
Web links
- Information on Nordwestreisemagazin.de
- Water balance of the North Sea islands on Uni-Oldenburg.de