Author(s): Rapaglia John
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Keywords: Groundwater discharge; Venice; Barrier lands; Subterranean estuary; Seepage meters
Abstract: Movement of groundwater beneath the barrier lands of Cavallino, Lido, Pellestrina, and Chioggia are a source of water and dissolved chemicals between the Adriatic Sea and the Venice Lagoon. Direct measurements of seepage meters and piezometers showed that there is a tidally dependent flow of water from the Adriatic to the lagoon and vice versa. Because of the phase shift in tidal elevations between the sea and the lagoon, the sea level is higher than the water level in the lagoon for up to three hours at a time. The differential hydraulic head among the bodies drives a flow of salty water beneath the barrier islands. The volume flow appeared to be facilitated by the highly porous infill material of former inlets which represent high-permeability conduits of exchange. The “Mose” project which, when finished, will separate the lagoon from the sea during times of high water, may prolong and enhance these periods of differential hydraulic gradients, driving sea water into the lagoon. Any time salt water comes in contact with sediment, chemical reactions take place allowing for, among other things, the desorption of particle reactive compounds from the sediment. This flow therefore may also be a source of contamination for the lagoon.
Year: 2007