Page 7 - Barrocu_2003
P. 7
SEAWATER INTRUSION IN THE COASTAT AQUIFERS OF ITALY
and zinc sulphide ore district in Europe. To enable ing. When evaluating the adverse effects of
to mining operations to be continued below sea groundwater overabstraction, facts other than the
level, the water table was lowered to –200 m by amount of fresh groundwater withdrawal in rela-
pumping salty groundwater up into a drainage tion to groundwater recharge should be consid-
tunnel at 15 m above sea level. Around 1600 1/s, ered. In fact salt water encroachment is con-
mainly saltwater intruded from the sea, were dis- trolled by aquifer attributes, namely its geometri-
charged into the Mediterranean. Groundwater cal and hydraulic parameters, solid and liquid
salinity was 11 g/l, while at the end of the 19th phase composition, mechanisms and times of
century, prior to the water table drawdown to natural and/or artificial recharge, and by well
below sea level, a salinity of 0.113 g/l had been characteristics such as well diameter and depth in
measured. Mining activities were eventually relation to interface level and the influence
abandoned and in the mid 1990’s the pumping radius of resultant well draw down in relation to
station at –200 m below sea level was shut down. well distance from coast line. Furthermore, wind-
Subsequently a new piezometric surface of the borne saltwater spray depositing on the soil may
freshwater floating on top of the seawater is now be conveyed by infiltrating rainfall into surficial
reaching a new equilibrium level. At present, a groundwater.
freshwater flow of 280 l/s is abstracted from the
aquifer and conveyed by aqueduct to city of Overpumping in coastal areas has caused
Cagliari. major problems in urban and industrial zones, like
the metropolitan areas of Venice-Marghera and
SEAWATER INTRUSION IN ITALY Ravenna, where, in order to satisfy industrial and
municipal water demand, the local alluvial multi-
Saltwater intrusion has jeopardized to a layered aquifer systems have been so seriously
greater or lesser extent most coastal aquifers in depleted that their piezometric surface has been
the Italian peninsula and its islands, as shown in lowered by hundreds of meters. This has resulted
figure 1. in the progressive intrusion of saltwater, which is
now found at various depths depending on the
All along the coasts of Italy, the post-glacial zone, and also in land subsidence locally, to the
sea level rise brought about by the general climate extent that Venice and Ravenna are now threat-
change led to the formation of delta plains con- ened by sea flooding (Gatto & Carbognin, 1981;
sisting chiefly of fluvial, lacustrine and evaporit- Carbognin & Tosi, 1995; Mar-tinelli et al. 1998).
ic deposits in salty and brackish environment. Efforts are now being made to halt groundwater
Under the present hydrodynamic balance between exploitation.
fresh and salt surface and groundwater, those
deposits, entrapping brine and connate salt The deltaic areas where aquifers are jeop-
waters, remain unleached, so that even fresh ardized to a varying extent by saltwater intrusion
waters of lateral inflow from inland aquifers include the coastal plains of Tuscany (Maremma,
towards the sea become salty when seeping Valle del Magra, Corna, Ombrone, and Albegna
through them. Different permeability horizons plains, Castiglione della Pescaia, and the Island of
corresponding to different karst drainage patterns Elba), Latium (especially the river Tiber delta and
depending on sea level variations over time have the Pontina Plain), Campania, Calabria, Sicily
been recognized in Middle Cambrian to Recent (Augusta-Syracuse, Palermo, and Marsala), and
limestone formations. Sardinia (the Flumendosa delta, and the bays of
Cagliari and Oristano).
Overpumping is generally considered a
major cause of saltwater intrusion, due to both Saltwater has also invaded the karst aquifers
freshwater table draw down and saltwater upcon- of Apulia (Gargano, Murgia, Tavoliere, and
Salento peninsula), Sicily (Hybleans and Paler-
mo), and Sar-dinia (Alghero), and the volcanic
213
