18th SWIM, Cartagena (Spain), 31 May - 3 June 2004

MODELING STUDY OF The SEAwater intrusion IN THE MURAVERA COASTAL PLAIN (SE SARDINIA, ITALY)

GIUDITTA LECCA1, PIERLUIGI CAU2 AND FEDERICA ARDAU3

1. HYDROLOGY AND WATER RESOURCES MANAGEMENT, DEPT. OF ENVIRONMENTAL AND IMAGING SCIENCES (EIS), CENTER FOR ADVANCED STUDIES, RESEARCH AND DEVELOPMENT IN SARDINIA (CRS4), P.O. BOX 10, 09010 PULA (CAGLIARI), ITALY, TEL. +39709250272, [email protected]; 2. GEOGRAPHICAL INFORMATION SYSTEMS, EIS, CRS4, [email protected]; 3. DEPARTMENT OF TERRITORIAL ENGINEERING, UNIVERSITY OF CAGLIARI, ITALY, [email protected].

Abstract: The Muravera plain is located at the mouth of the Flumendosa river in the South-Eastern part of the Sardinia island and covers an area of about 130 km2. The population of the main centres of the plain (Muravera, Villaputzu and San Vito) is comprised of 13000 residents and dramatically increases during summer. Apart from tourism, traditional economic activities are farming, sheep and goat grazing, and citrus fruit growing. The complex stratigraphy of the plain is chiefly composed of Quaternary alluvial deposits (up to a few hundreds meters thick) which overlay the Palaeozoic bedrock outcropping at the edges of the plain. Climate is Mediterranean subtropical, characterized by a strongly variable rainfall regime with annual precipitation fluctuating between 200 and 700 mm. Saltwater encroachment in the coastal aquifer and salinisation of soils were first observed in the `70s and correlated with a significant lowering of the groundwater table. Likely causes of saltwater intrusion are both anthropic (upstream damming of the Flumendosa river and its tributaries, aquifer overexploitation, and fish-farming) and natural (recurrent droughts and deep salty geological formations). Currently both the phreatic and confined aquifers are heavily contaminated by saltwater and data collected during the last 20 years show a salinisation process steadily moving landwards. As a result, extensive citrus plantations have been irremediably damaged and other cultivations have been severely affected. Remedial measures are being considered by the local agency for the management of water resources, including withdrawal rationalisation, creation of a district irrigation network, artificial recharge with treated wastewater and hydrodynamic barriers. A modeling study based on a three-dimensional density- dependent flow and contaminant transport code is currently being implemented for this site. The aims of this study are to improve the understanding of the groundwater degradation mechanism within the complex hydrodynamic system (diverted upstream surface waters, lagoons and channels) of the coastal plain and to support the decision between the proposed remediation strategies by means of simulated alternative scenarios.

Keywords: numerical modelling, seawater intrusion, density-dependent subsurface flow and contaminant transport, integrated management of water resources.

Acknowledgements. This work is funded by the project Sustainable Water Management In Mediterranean Coastal Aquifers (SWIMED): Recharge Assessment and Modelling Issues (EC INCO contract no. ICA3-2001-20004), and by the Sardinian Regional Authorities.

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