Ghyben Herzberg Relation for Saltwater Interface

Reference

In coastal aquifers, fresh water floats on denser seawater, and the Ghyben Herzberg relation says every meter of fresh head above sea level pushes the salt interface forty meters down.

The equation

z = 40 h
  • z is the depth of the interface below sea level in meters
  • h is the fresh water table height above sea level in meters
  • 40 comes from the density contrast between fresh and sea water

Worked example

A well field that lowers the water table from 0.8 to 0.5 meters above sea level lets the salt interface rise from 32 to 20 meters below sea level. Twelve meters of upconing from a 0.3 meter change at the surface.

When to use it

A sharp interface approximation that ignores the mixing zone, but it captures the alarming leverage of coastal pumping. Use it to screen abstraction plans before running a density dependent model.

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