Geoscience Reference
In-Depth Information
Fig. 17.5 Sketch of the salinization mechanism in a coastal aquifer, where t is the hydraulic head
and the subscripts t, s, and r denote transition zone, groundwater, and reference depth,
respectively; color code: darker gray indicates higher salinity (Tulipano and Fidelibus
2002
)
Another example of groundwater salinization by lateral seawater intrusion, in
the coastal karstic aquifer of Salento peninsula (Italy), is reported by Tulipano and
Fidelibus (
2002
). As a result of continuous over-exploitation between the years
1974-1996, progressive groundwater salinization was observed, associated with a
discernible reduction in the amount of freshwater in the aquifer. As conceptualized
in Fig.
17.5
, over-exploitation of groundwater induces the upward migration of
groundwater and prevents groundwater flow toward the coast. If the weight of the
freshwater column reaches a value able to prevent the salt water intrusion, the
system may reach equilibrium. However, continuous over-exploitation favors
extensive salinization of a coastal aquifer.
From the above examples, it may be understood that salinization of ground-
water by seawater intrusion is a global phenomenon, due mainly to anthropogenic
over-exploitation of coastal aquifers. Analyzing various coastal aquifers, Werner
et al. (
2012
) suggest that seawater intrusion can be predicted on the basis of several
vulnerability indicators: (1) Seawater volumes entering flux-controlled, unconfined
aquifers, subject to small rises in sea level, can be approximated by the saltwater-
freshwater interface toe length multiplied by the rise in sea level; (2) sea level rise
in head-controlled, unconfined aquifers produces higher rates of seawater intrusion
(toe movements and seawater volume changes) compared to flux-controlled
unconfined aquifers; (3) in unconfined aquifers, flux-controlled boundary condi-
tions produce a larger toe response to changes in recharge than head-controlled
boundary conditions; (4) sea level rise is inconsequential in confined aquifers that
are flux-controlled. The authors note that in addition to the anthropogenic factor of
coastal aquifer over-exploitation, coastal aquifer vulnerability is subject to the
threat of sea level rise from climate change.
Under the conditions described in
Sects. 17.1.1
and
17.1.2
, is groundwater
salinization an irreversible process? Theoretically, the level of a freshwater aquifer
may increase following a rainy season or by infiltrating the land surface with
additional excessive amounts of freshwater. As a result, in coastal aquifers, the
higher water table could be expected to drive flow seaward and lead to reversibility
