Island and Coastal Aquifers - Hydrogeology: Objectives, Methods, Applications - page 62

C HAPTER A9
Island and Coastal Aquifers
1 THE INTERSECTION OF TWO ENVIRONMENTS
The water in aquifers, when they are recharged, circulates towards the local
base level. On islands and in coastal zones, aquifers therefore fl ow out into
the sea. However, an aquifer being, by nature, permeable, sea water can
also fl ow into it. The two environments will therefore interact following
theoretically simple laws, which, in practice, become highly complex,
particularly for karst aquifers. The penetration of sea water into a coastal
aquifer can sometimes have irreversible effects.
1.1 Distribution and economic importance
Coastlines tend to be densely populated, and the economic importance
of these aquifers is constantly increasing, but their use is restricted by the
problem of contamination by sea salt. The particular case of coastal karst
aquifers must be highlighted here. Numerous high-yielding springs, located
in the most populated zones, cannot be used due to their high salinity. Port
Miou (8 m 3 ·s -1 ) near Marseille and the Almyros (10 m 3 ·s -1 ) near Iraklion
(Crete) are two examples, which have been the object of numerous projects
and studies for almost half a century without resolving the problem.
In just the Mediterranean Sea, it is estimated that 1,000 m 3 ·s -1 of water
pours out from karst aquifers into the sea, generally at a total loss. Given an
individual consumption of 250 L per day, such an amount could theoretically
have served over 350 million people.
1.2 Saltwater intrusions
In a porous or fractured aquifer, the two environments, protected from
turbulence, do not mix often. Porous coastal aquifers were studied at the