The Exploitation of Aquifers - Hydrogeology: Objectives, Methods, Applications - page 188

Figure 100 Hydraulic barrier created by injection in a coastal aquifer.
4.2 Coastal karst aquifers
4.2.1 Detection of sub-marine emergences
Springs large enough to be of economic value are clearly visible at the
surface, where they form rings. They are therefore known to the locals,
and inquiries with fi shermen enable the fi nding of their location. For the
smaller springs, various detection methods are in use:
￿ temperature: during the summer, sea water heats up rapidly at the
surface, while karst waters remain at a constant temperature. They
can therefore seem very cold and can be felt by swimmers. In the
winter, the reverse is the case. In situ temperature measurements, or a
thermal imaging survey from the air, allow the detection of freshwater
emergences during the summer or winter, when the thermal contrast
between the two waters is the greatest;
￿ salinity: salinity differences can easily be found using conductimetry;
￿ coastal geomorphology: a notch (visor) cutting into limestone at the
edge of the water is almost always associated with a nearby spring.
4.2.2 Exploitation
a) Diversion at the outlet
Direct exploitation at the outlet is rarely possible due to the salinity. Attempts
to cap the emergence with a resin bell were undertaken at the Galeso spring