Saltwater Intrusion of Reclaimed Agricultural Land in the Venice Lagoon, Italy

This research project is being conducted by James Lea Bevington, an Environmental Engineering graduate student at the University of Georgia. He will be in Italy from December, 2013 to August, 2013.

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The purpose of this project is to develop a better understanding of saltwater intrusion and contamination of groundwater and its effects on agriculture. This knowledge will be embodied as a model to help in future management efforts. The intrusion of saltwater is expected to increase due to sea-level rise. Meanwhile, demand for agriculture is also expected to rise because of emerging nations and bio-fuel production. The majority of our planet’s population lives near the coast and the management of these areas is of utmost importance.

Venice was constructed on a series island which provides isolation from the main land. This protected them from enemies who must cross the lagoon to get to the city center. Venice became a center for commerce due to its location and naval access. They were a major trading center between Europe and the east, a position that gave them great wealth and power.

Because of their isolated location, the Venetians have a history of studying and modifying their surroundings. The problem is that they don’t always get it right. One of the major modifications was the rerouting of rivers to discharge outside of the lagoon. The rivers brought sediment to the lagoon which settled out of suspension and fell to the bottom. The sediments gradually add up over time and the venetians feared that the main land would soon connect to the island. The sediment also made navigation difficult for the ships that stopped to port there. More recently, there have been several projects which have reclaimed land around the edges of the lagoon.

Bevington diagram 2The undertakings of the past have left Venice in a dire position. The area is suffering greatly from subsidence, an issue that is of great concern. There are three main causes of subsidence, geological subsidence, anthropometric subsidence, and sea level rise. Geological subsidence caused by tectonic processes and averages only 0.5 mm/yr which is only a small component. Anthropometric subsidence is the result of rerouting the rivers, pumping gas and water from the ground, and the consolidation of soils. The sediment provided by the rivers fought the effects of subsidence because it refilled the sunken areas. Over use of groundwater aquifers was mostly stopped in the 1970’s but the damage has already been done.  Soil consolidation occurs because of the high salinity water and the drainage of water from land to be used for agriculture. The presence of high salinity water is due to low flow rates in the river from upstream use and because the freshwater rivers no longer mix in the lagoon. Anthropometric subsidence rates are up to 30 mm/yr in some places. Sea-level rise is responsible for 1.5 mm/yr subsidence (Carbognin et al, 2005).

Sand percentage figureSubsidence has left several areas with an elevation below sea-level. The elevation difference combine with the higher density of saltwater provides a hydraulic pressure which pushes inland. If the water flows inland it can contaminate aquifers and have negative effects on crop production. Sandy soils conduct groundwater flow while clayey soils retard flow. The hydraulics of a particular site are highly dependent on the type of soils present. Typically physical cores are used to study soils but this is intrusive and not practical on a large scale.

This research, in particular, is aimed at relating soil core data to remote sensing techniques like electromagnetic induction (EMI). This will allow for the prediction of soil characteristics such as grain size distribution, pH, conductivity, and organic content at the field scale. This will be accomplished by extrapolating soil core measurements in relation to EMI results. Preliminary work has discovered the presence of sandy paleochannels which causes large heterogeneity of the soil.

Carbognin, Teatini, & Tosi. (2005). Land Subsidence in the Venetian area: known and recent aspects. Giornale di Geologia Applicata 1, 5-11.