Salt water intrusion in coastal aquifers of the Venice coastland

The investigations carried out since the early '970 showed that salt water intrusion affected most of the Venetian coastal area. However, at that time, phenomena such as land subsidence and flooding (known as "acqua alta") had the priority in relation to the city protection, thus the study of the salt water intrusion process assumed a secondary role. During ,,990, the salinization process became the subject of a research project performed by the Institute of Marine Science (ISMAR CNR-National Research Council). The results revealed a severe hydrological situation, particularly critical in the southern region. Aware of saline contamination effects on the environment and the agricultural activities, mainly horticultural crops well developed around Chioggia, the Venice Province started in 1998 the "Saline Wedge Project" to understand the consequences of the salt water intrusion in the subsoil, in connection also to land subsidence, at the southern part of its territory. The knowledge acquired by the two institutions (Venice Province Authority, ISMAR-CNR) constituted the common basis for new research and monitoring projects. Several meetings were promoted to involve all the authorities and institutions responsible for land management to raise awareness of the saline contamination and its environmental and socio-economic impact, and to highlight the need of establishing appropriate monitoring networks in critical areas. In the southern sector, where the possible damages for the agricultural-horticultural activities could be economically relevant, two projects (Saline Wedge 1998-2000; ISES Project 1999-2002) were initiated in the late ,,990, involving all the authorities managing the territory. The aims of these projects were a) to increase the knowledge on the factors enhancing the salt water intrusion; b) determine the areal extent of the saline contamination; c) assess the critical conditions in relation to the economic activities, mainly of agricultural and tourist type. Once obtained a detailed hydrogeological representation, specific actions to limit the process have been planned (Brenta Project, 2003-2004). Preliminary investigations were performed to realize a mobile gate at the mouth of the Brenta-Bacchiglione river to prevent the encroachment of sea water into the river bed during high tides. More recently, scientific efforts have been devoted to better understand the process dynamics. Mathematical models have used to investigate the effects of other possible mitigation strategies (CORILA Project 3.10 2004-2007; VECTOR-Cliven Project 2007-2010). In the northern sector of the Venice territory, between the Piave river and the lagoon margin, researches aimed at improving the comprehension on the salt water intrusion phenomenon started in 2004, thorough the cooperation between the University Ca" Foscari of Venice and the University of Padua (PRIN Project "The deep aquifers of the Po Valley as regional resource: aquitard in hydrodynamics, generating of water chemically and thermally anomalous, a suitable place for the CO2 atmospheric trapping"). The combined use of adequately validated geophysical and geochemical tools conferred a multidisciplinary character to the research and allowed for the definition of the phenomenon"s superficial extension. Geophysical analysis based on Vertical Electrical Sounding (VES) and conductivity logs have been performed together with water table measurements and geochemical analysis on samples collected from selected wells. Moreover, a critical review of old geophysical data allowed for the verification of possible saline contamination changes in time. Interesting results have been obtained specifically within territory of Jesolo. In this case, considering the influence of the Piave and Sile rivers and the presence of a coastal sand dune, a map of salt water contamination was created to evaluate the agricultural use of superficial water. The effective origin of salt water found in the aquifers, its distribution, extension and its preferential way of movement within the territory were defined relating all the information acquired to the geological, geomorphological and stratigraphic characteristics of the area In addition, the presence of salt water contamination in the shallow aquifers below the city of Venice has been highlighted by recent studies developed at the IUAV University.