Monitoring fresh/saline groundwater

Primary challenge owner: Province of Fryslân

Secondary challenge owner(s): None 



A large part of the Dutch coastal zone contains shallow salt/brackish groundwater. Above the saline/brackish groundwater, rainwater lenses will form. This rainwater lens is bordered at the bottom by a barrier, where the freshwater is able to pass relatively quickly to the brackish/saline water present in the subsurface. In areas with strong seepage and in dry summers, this rainwater lens can disappear (the boundary surface rises), causing agricultural crops to face saline groundwater. This has a negative effect on crop size and quality. 

With the current measuring methods the displacement of this boundary (and with it the thickness of the rainwater lens) cannot easily be monitored continuously. One consequence is that, as a result, the effects of interventions in the hydrological regime cannot be properly determined.


The question/challenge for startups

Develop a measuring instrument, which allows continuous detailed monitoring of the course (profile) of salinity in depth.



  • The instrument must be able to be used under field conditions and to make reliable measurements over a period of at least 5 years, without losing reliability due to moisture, wear, temperature fluctuations, etc.
  • The instrument should be easy to place and readable by a field worker. The energy supply can power the measuring instrument for at least half a year and is easily rechargeable if necessary. 
  • The depth range at which reliable measurements can be made is at least 5 meters. 
  • The cost of the tool is not a barrier for application in a project setting on an unmanaged arable field.
  • The measuring instrument does not disturb the subsurface (and with it the readings) to such an extent that it affects the reliability of the readings.

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