Pump It Up

/ by Ted O'Callahan /

How to stop Venice from being swallowed by the sea.

Venice, unflooded.  Credit: Pauline Vos

Venice is sinking beneath the sea. But a group of engineers believe that sea water, itself, may be the best way to save the city.
Giuseppe Gambolati heads a team of researchers who, last month, presented city leaders with a proposal to inject sea water into an aquifer deep below the city. He predicts this will raise the ground level as much as 30 cm over the course of 10 years.

Gambolati has worked on land subsidence issues for 30 years and he says that the technique has been used effectively in other places where the ground has begun to sink. He cites Long Beach, California, where subsidence (sometimes 9 m deep) resulted from oil production; they’ve been using water injection successfully since the 1950s.

A hundred years ago, high waters flooded the Venice’s central square only a handful times each year. John Keahey, author of the book Venice Against the Sea, says that city residents have traditionally felt that the occasional flooding was just a part of life in the Italian city. 

“The water comes and the water goes,” Keahey said. “They will happily put on their boots and trudge through.”

But the issue has gotten much worse in the last 50 years. In 1966, there were 99 major floods; most years now see at least 40 acqua altas (literally, “high waters”).

To compound things, the ocean level is rising. The Adriatic Sea around Venice is 11 cm higher than it was 100 years ago. That’s in addition to the 12 centimeters of subsidence over the last century, much of it due to pumping fresh water out of aquifers.

Gambolati says that the solution is to reverse the process.

“Pumping water in is the same as pumping water out, with the effect reversed,” he said.

According to Gambolati’s team, if Venice had been just 30 centimeters further above sea level, 94% of the acqua altas since 1910 would have been avoided.

In 2003, Italian Prime Minister Silvio Berlusconi set in motion an operation named MOSE, after Moses’ parting of the Red Sea. The project, scheduled for completion in 2011, will place mobile barriers across all three openings of the lagoon that protects Venice from the Adriatic. Hidden most of the time, the barriers would be raised to block the highest tides and storm surges.

The initial price tag for MOSE ws $3 to $4 billion, but it is now expected to cost $6 billion. The mayor of Venice is calling for cost-effective alternatives.

Gambolati’s project is budgeted at $117 million, but he sees it as a complement to MOSE, not an alternative. The engineers would be drilling a series of 12 vertical wells to depths of 650 to 800 m. The researchers say that the brackish aquifer of water-saturated, sandy material is a promising repository for the sea water injection because it is sealed above and below by layers of very low permeability. Roughly equivalent to the pneumatic cushions of some sneakers, the pressure created by pumped water forced between the sealed layers would allow Venice to be raised on a cushion of water. 

While skeptics are concerned that raising the city unevenly will damage Venice’s buildings and structures, Gambolati says satellite technology will allow continuous real-time monitoring, permitting engineers to calibrate the injection rate to keep the lift balanced.

Keahey says the project has many obstacles to overcome, but he added, it is the first time somebody of Gambolati’s stature has brought forward such a detailed proposal.

Originally published December 12, 2005

Tags development engineering research

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