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University IUAV of Venice – Faculty of Architecture

20th SWIM Salt Water Intrusion Meeting. Naples, Florida, USA - June 23-27, 2008. Salt Water Intrusion in The Shallow Aquifers of Venice. F. Zezza, E. Di Sipio. University IUAV of Venice – Faculty of Architecture.

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University IUAV of Venice – Faculty of Architecture

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  1. 20th SWIM Salt Water Intrusion Meeting Naples, Florida, USA - June 23-27, 2008 Salt Water Intrusion in The Shallow Aquifers of Venice F. Zezza, E. Di Sipio University IUAV of Venice – Faculty of Architecture

  2. Aim of this research is to determine the water circulation of the first 50 m depth of the Venice town subsoil • to determine shallow aquifers presence and thickness • to analyze salt water intrusion and influence of tide variations • to characterize the different hydrochemical facies of perched and confined aquifers

  3. The city of Venice (Po plain, NE Italy) is located in the southern threshold of the Veneto Platform (from Brambati et al., 2003, modified)

  4. lack or fragmentation of geological interpretation in the first 50 m of depth the upper Quaternary stratigraphical sequence is characterized by a great deal of variability in both the horizontal and vertical directions what is the hydrogeological characterization of the subsoil (first 50 m depth) ?

  5. Venice sedimentary structure The lithostratigraphic method allows to distinguish the cyclothemic organization, typical of lagoonal area, from the multistorey sandbody, typical of the city centre subsoil (from Zezza, 2007)

  6. groundwater circulation in the Late Pleistocene – Holocene deposits of Venice historical centre

  7. Well points • pH • T • EC • water level SGO=San Giacomo dall’Orio, SGB=San Giovanni in Bragora, SM=San Martino, PS=Punta della Salute, PL=Ponte dei Lavraneri (Giudecca), SE=Sant’Eufemia, San Marco, SC=San Cassian, SFV=San Francesco della Vigna, SB=San Basilio 61 piezometers: > 50 at 6-8 m depth the remaining under 12 m depth influence of tidal variations (Punta della Salute marigraph) San Basilio (SB) has been selected as sampling area

  8. perched aquifers: A • in landfill deposits (k=10-1-10-3 cm/s, thickness of 3.5-4 m) • widespread all over the city • water level ranging between 0.70-0.05 m m.s.l • directly connected with the lagoon tide fluctuations determines water level variations: PS1 tide PS4 • 60 cm near the channel bank (PS1) • 2-3 cm at a distance of 8-9 m (PS6) PS6

  9. perched aquifers: A • the rainfall contribution to recharge factor is observable only in the piezometers located inland (more than 8 m from the channel bank) relationship between water table, tide and rainfall for Punta della Salute (June 21- July 26 2001)

  10. perched aquifers: B • in semipermeable sediments at 6-8 m depth (aquiclude) • limited extension and thickness (about 2 m) • water table trend: between -0.70 and -0.80 m g.l. • influenced mainly by low tide San Cassian (June 18- July 17 2004)

  11. confined aquifers: C1-C2-C3 • in Pleistocene sand bodies deposits • not influenced by rainfall • the influence of tide fluctuations diminishes progressively with depth

  12. physical – chemical analyses San Francesco della Vigna (SFV): May 2005 San Basilio (SB, F): June 2007 EC Lagoon measurement (San Nicolò Channel) : 48,9 mS/cm (June 2007)

  13. physical – chemical analyses The EC/depth relationship for samples collected in the piezometers of San Basilio - Santa Marta area point out the existence of water salinization with depth

  14. geochemical analyses geochemical analysis in mg/l relationship between sea water and Venice water ions ratio San Basilio area

  15. geochemical analysis the Venice shallow waters, both of perched and confined aquifers, are chloride-sulphate-alkaline waters San Basilio the anion ternary diagram focuses the existence of a mixing process between fresh and salt water related to the increasing of Cl content

  16. Isotopic analysis San Basilio the isotopic analysis confirms the existence of a mixing process between fresh and salt water of marine and lagoonal origin

  17. Results • the hydrogeological characterization of the first 50 m of the Venice subsoil has been done • tide variations affects the water level in all the identified aquifers • the perched and confined aquifers are all interested by salt water intrusion • the Venice shallow waters have the same geochemical facies • the evolution process of the fresh water towards the composition of seawater is confirmed by the geochemical-isotopic analyses

  18. Future development • according to lithostratigraphic information, to improve the knowledge of contact zones between the different aquifers recognized • to collect more data to confirms the hydrogeological model presented • to focus on the soil-water interaction and its effects on buildings

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