Kouli_etal_2008_Groundwater modelling_BOOK.pdf - Pantelis ...

Groundwater Management in the Northern Adriatic Coast (Ravenna, Italy)… 211
et al., (1990, 1995(a)) have described the late Quaternary depositional history of this coastal
plain.
The deposits making up the phreatic aquifer are typical of coastal and delta areas with
sandy and silty unit intercalated (Marchesini et al., 2000) and sand dunes characterized by
north-south orientation, which today are visible up to 30 km inland. Aquifer’s thickness
varies from 8 to 30 meters (Antonellini et al., 2008). Generally, the lithologic reconstruction
of the study area shows a dominant sand composition with medium and fine grained sand
units characterizing the most part of the aquifer’s stratigraphy.
Slug tests and tidal well tests have been carried out in the most significant points of the
study area (2004-2007) in order to define the main petrophysical properties and evaluate full
scale aquifer hydraulic conductivity. We used the Bouwer and Rice slug test method
(Bouwer, 1976; 1989) that is suitable for screened wells in the unconfined coastal aquifer.
The results of the slug tests have been integrated with the lithological/stratigraphic
information and compared with tidal well test values of hydraulic conductivity obtained using
the method outlined by Fetter (2001) and Jacob (1950). Hydraulic conductivity estimates give
an average of 20 m/day (Giambastiani et al., 2007). This high hydraulic conductivity values
are in according with the stratigraphic records which show a dominant sand composition with
high porosity (0.15-0.35%) (RER and ENI-AGIP, 1998).
Water Budget
In order to estimate the water budget it is necessary to know all inflow and outflow
components in the catchment. Unfortunately due to the lack of accurate drainage and
irrigation information many data can only be deduced. Therefore the approach has been to
estimate local water budget taking into account only precipitations, evapotranspiration,
runoff, infiltration and pedologic features.
An end-of-the month water balance model called Watbal (Starr, 1999) was used to
calculate the components of the hydrologic water budget for several sites in the study area
(Antonellini et al., 2008; Mollema et al., 2003). This model is based on an energy balance
approach to estimate potential and actual evapotranspiration, soil water flux, soil moisture
content and deficit. The estimate of these parameters depends on several factors such as solar
irradiation, air humidity, wind speed and direction, soil composition and type of vegetation.
The average precipitation is 0.6 m/year and the mean temperature is 13.4°C and generally
the highest temperatures occur in the summer which is also the period with the least
precipitation. As a result the water budget calculations show a surplus only during the first
three months of the year when some water is able to seep down from the soil into the aquifer
below. In the other months of the year, nearly all precipitation is used by plants or evaporates
directly from the soil (Fig. 4)
Since the water to recharge the aquifer is available only a few months per year, the
aquifer recharge is small (14-17 mm/year) and it is insufficient to create a significant
freshwater head.
Moreover Ranjan et al. (2006) prove that pine forests along coastline zone can affected
negatively the water quality in the phreatic aquifer. In fact dense vegetation results in strong
evapotranspiration and decreases the recharge of the aquifer; the pumping made by tree roots
encourages saltwater intrusion from the sea and from the bottom of the aquifer also.