The present work deals with the numerical model of the plio-pleistocenic aquifer of the River Albegna coastal plain (southern Tuscany, Italy) which is constituted by gravelly-sandy levels confined by silty-clayey deposits (aquitards), and overlay prevalently on Pliocene marine clays. The aquifer has been exploited progressively for irrigation and tourist uses, with an overall withdrawal which has reached about 3•106 m3/year, and has caused a remarkable po-tentiometric drawdown with the appearance of a wide seawater intrusion, showed by the degradation of the chemical quality of the groundwater. The acquisition, organization and interpretation of the data have lead to the definition of the conceptual model of the aquifer. The water recharge arises from infiltration of rainfall that falls on the model, lateral flows due to the rain that is infiltrated in the external outcrops of the aquifer levels and flows from the adjoining carbonate aquifer. The natural outflow occurs through diffuse flow into the sea and river; artificial outflow occurs through intensive extraction of groundwater by wells. Inside the aquifer water exchanges occur by natural (leakage, closing of aquitard) and artificial caus-es (multiscreened wells). The aquifer system was represented by 3D numerical finite element model using the software FEFLOW. The model was calibrated for steady and transient states by matching simulated and observed piezometric levels over the period available (february 1995 - february 1996). The model allowed to evaluate the water balance of the system and to emphasize that the seawater intrusion is essentially due to withdrawal concentrated near to coast and during irrigation season which draws saline water above all in the Osa-Albegna sec-tor (almost 3•105 m3), with the addition of intrusions along the river which at times feed the aquifer (about 6•104 m3). Piezometric levels of february 2003 were used for model validation. To predict the aquifer responses to hypothetical scenarios of exploitation for the period of 2003-2033, two different hypothesis of use were investigated, considering actual negative trend of precipitation.
Modellizzazione numerica del sistema acquifero della pianura costiera del fiume Albegna (Toscana meridionale)
NOCCHI, MONICA;
2005-01-01
Abstract
The present work deals with the numerical model of the plio-pleistocenic aquifer of the River Albegna coastal plain (southern Tuscany, Italy) which is constituted by gravelly-sandy levels confined by silty-clayey deposits (aquitards), and overlay prevalently on Pliocene marine clays. The aquifer has been exploited progressively for irrigation and tourist uses, with an overall withdrawal which has reached about 3•106 m3/year, and has caused a remarkable po-tentiometric drawdown with the appearance of a wide seawater intrusion, showed by the degradation of the chemical quality of the groundwater. The acquisition, organization and interpretation of the data have lead to the definition of the conceptual model of the aquifer. The water recharge arises from infiltration of rainfall that falls on the model, lateral flows due to the rain that is infiltrated in the external outcrops of the aquifer levels and flows from the adjoining carbonate aquifer. The natural outflow occurs through diffuse flow into the sea and river; artificial outflow occurs through intensive extraction of groundwater by wells. Inside the aquifer water exchanges occur by natural (leakage, closing of aquitard) and artificial caus-es (multiscreened wells). The aquifer system was represented by 3D numerical finite element model using the software FEFLOW. The model was calibrated for steady and transient states by matching simulated and observed piezometric levels over the period available (february 1995 - february 1996). The model allowed to evaluate the water balance of the system and to emphasize that the seawater intrusion is essentially due to withdrawal concentrated near to coast and during irrigation season which draws saline water above all in the Osa-Albegna sec-tor (almost 3•105 m3), with the addition of intrusions along the river which at times feed the aquifer (about 6•104 m3). Piezometric levels of february 2003 were used for model validation. To predict the aquifer responses to hypothetical scenarios of exploitation for the period of 2003-2033, two different hypothesis of use were investigated, considering actual negative trend of precipitation.
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