Fighting Water with Water: To lift the city, pump the sea beneath Venice

With technology commonly used in oil fields, engineers say they could inject seawater into sandy strata deep beneath Venice, Italy, to boost the subsiding ground that now aggravates flooding there.

Venice, which is known for its architecture, bridges, and gondola-filled canals, is slowly losing ground. Over the past century, land beneath the city subsided almost 12 centimeters, and the sea level rose almost 11 cm. That net increase in water level significantly exacerbated flooding, says Giuseppe Gambolati, a hydrologist at the University of Padua in Italy.

One government-approved project to protect Venice includes inflatable barriers that will be raised when severe storms boost the water level in the surrounding lagoon more than 1.1 meters above sea level, says Gambolati. Despite its multibillion-dollar cost, that future system isn’t designed to protect Venice against smaller floods. Even when waters reach only 80 cm above sea level—which they do dozens of times annually—the plaza in St. Mark’s Square is submerged.

At many sites around the world, the oil-drilling industry injects large volumes of water into petroleum-bearing rocks to increase the pressure there and ease the extraction of oil. That technique often prevents ground overlying the oil from subsiding and sometimes even pushes the ground upward, says Gambolati. In the Sept. 28 Journal of Geophysical Research (Earth Surface), he and his colleagues propose that the technique could reduce the frequency of Venice’s flooding.

Several layers of sandstone that contain brackish water lie between 600 and 800 m beneath Venice. Injecting seawater into those porous strata would increase water pressure there, partially relieving the weight of earth above and permitting the rocks to expand. Using a computer model, the researchers found that pumping 35 liters of water per second through each of 12 deep wells located about 5 kilometers from the city, could lift Venice between 11 and 40 cm over the course of a decade.

The most probable scenario is a boost of about 25 cm. Historical sea level data covering more than 140 years suggest that this elevation would reduce the city’s flooding above the 1.1-m benchmark by about 90 percent, says Gambolati.

Such a project “sounds plausible,” says Gerald W. Bawden, a geophysicist with the U.S. Geological Survey in Sacramento, Calif. Pumping meltwater in the springtime from rivers into aquifers in the Los Angeles basin—which stores the water until it’s withdrawn later in the year—lifts the surface of the ground in some areas as much as 6 cm (SN: 8/25/01, p. 119: Available to subscribers at L.A. moves, but not in the way expected), he notes.

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