Kouli_etal_2008_Groundwater modelling_BOOK.pdf - Pantelis ...

Groundwater Management in the Northern Adriatic Coast (Ravenna, Italy)… 217
It will be difficult to create models that will exactly reflect or predict measured salinity
values in a particular place and time. This discrepancy of measured and modeled data already
observed (Giambastiani et al., 2007) is due to the lack of sufficient monitoring data,
especially at depth, and due to strong variations in salinity that are caused by weather events
(draught or rain) and that do not show up in the models. The complexity of the area with
many hydraulic structures close to one another further worsens the situation.
Causes and Effects
Our studies indicate that the natural and anthropogenic processes involved in saltwater
intrusion along the Northern Adriatic coast are:
Coastal erosion. Due to the scarce sediment supply (ARPA 2002), most of the Adriatic
coastline is under erosion. Many coastal defenses have been used to preserve the beaches
(dikes, breakwaters and artificial nourishments) but the erosion is not halted. Coastal erosion
brings the sea inland, diminishes the areas of recharge, and the volume of the aquifer
contributing to the increase in groundwater salinization.
Drainage. Land reclamation drainage to allow for agriculture causes a drop in hydraulic
head and aquifer’s freshwater recharge allowing for the upconing of the brackish-freshwater
(Fetter, 2001).
Well pumping. Some coastal zones not yet connected to the aqueduct continue using
water coming from wells in the phreatic aquifer for sanitary and domestic use. Lowering the
piezometric level in proximity to the wells allows saltwater upconing into the aquifer from
underlying higher density saline waters (Bear et al., 1999).
Coastal dune destruction. Dunes are the first line of defense against seawater ingression
especially in an area where most of the territory is below mean sea level. In addition, thanks
to their topographic elevation and good infiltration capacity, dunes provide freshwater
recharge and act as a hydrostatic barrier against the saltwater intrusion according to the
Ghyben-Herzberg principle (Fetter, 2001). The lateral continuity of the dunes system is also
important for creating a continuous freshwater lens along the coast. Unfortunately, the dunes
have been almost completely destroyed by tourist development, building of roads, sport
resorts and parking lots close to the beach.
Encroachment of saltwater along rivers and canals open to sea. Saltwater intrusion
occurs in the groundwater as well as along surface water bodies (Schijf and Schonfeld, 1953).
Due to the lack of proper bathymetric gradients (land subsidence reversed the gradients in
proximity to sea), the rivers in the study area have low discharge velocities. Their mouths
have been deepened and widened to permit the construction of tourist marinas. Furthermore,
rivers provide most of the irrigation water for agriculture, so that the natural river discharge is
reduced almost to zero during the irrigation season (May-September). In this situation,
saltwater encroachment is facilitated; once the salt wedge has penetrated far enough inland, it
can pollute the phreatic aquifers in contact with the river’s bottom (Schijf and Schonfeld,
1953; Armi, 1986; Baines, 1995)