Venice Keeps Adriatic at Bay [Engineering flood defence

Abstract

Hydraulics company Enerpac created caissons for three of the four barriers. It developed a damping and levelling control system, with four cylinders at each corner of the caisson and hydraulic accumulators, which absorb forces as the huge structure is placed onto metal sliding plates mounted on concrete mats positioned on the seabed. The control system cushions the momentum caused by lowering the caisson and an algorithm stops residual wave momentum from dislodging the caisson while it is being positioned. A watertight seal between caissons allows a service tunnel for maintenance once the project is complete. Construction work for the MOSE project began in 2003 and was scheduled to be completed in 2011, but delays - from environmental and conservationist challenges as well as bribery and corruption scandals, have resulted in a 10-year slippage and an increase in budget from euro1.6bn to euro5.5bn (around £4.8bn). Raising the gates takes 30 minutes and they remain closed for around four to five hours each time. The barriers have been tested every day since December last year, when they proved effective against high tides of 1.35m. The barriers are raised when there is a forecast of high water above 1.3m. In December 2020, incorrect forecasts of 1.2m-high tides meant that the gates were not raised and 1.37m-high waters flooded parts of the city. At the time, Venice's mayor, Luigi Brugnaro, said that the project is still being tested and that protocols would be developed to activate the defence system sooner. It was activated again shortly afterwards to protect the city from a 1.2m tide the following week. MOSE is scheduled to be fully operational by the end of this year to protect historic buildings and Venetians' businesses from the Adriatic Sea.