Island and Coastal Aquifers - Hydrogeology: Objectives, Methods, Applications - page 64

The penetration of salt water can occur over several kilometers into the
interior of the continent, depending on the geometry of the aquifer and the
hydraulic gradient, but also on the mineralisation of continental waters,
which increases with depth (see chap. A 10).
1.3 Anthropogenic actions
Exploitation modifi es the piezometric surface and causes the establishment
of a new equilibrium and the migration of the saltwater intrusion. Extraction
by pumping causes a vertical rise of the intrusion under the pump, around
40 times the drop in the water table (Figure 35). The discharge must therefore
be very precisely adjusted in order to limit drawdown.
Figure 35 Saline contamination due to pumping in a coastal aquifer.
The penetration of salt water can occur over several kilometers (Figure
36). In touristic areas, coastal resources are massively drawn upon during
the summer, the period during which the aquifers receive little recharge.
The risk of saline intrusion therefore increases, particularly given that, the
water table being close to the surface, private wells are often numerous.
On the Atlantic coast, salt water intrusions affect the aquifers of the
Gironde estuary (Soulac and Rochefort regions). On the Mediterranean, this
risk is present for most coastal aquifers, between Perpignan and Fréjus. For
example, the Astien aquifer, between Agde and Béziers, an important water