Venice has always suffered from flooding due to storm surges, now increasing in magnitude and frequency due to sea level rise and land subsidence (0.15 + 0.10 m in the last century). St. Mark's Square (level M.S.L. +0.8 m) is now flooded over 40 times per year and nearly all the old city is underwater when the sea level exceeds + 1.5 m, as occurred on 4th November, 1966 when level M.S.L. + 1.94 m was reached with catastrophic consequences. Small variations in sea level (a few decimetres) can cause huge damage.

The project for the safeguarding of Venice and its lagoon forms one of the largest and most complex projects in the world. Careful account must be taken of the priceless artistic, architectural and historical heritage, the industrial and port development, the tourism and commercial activities, and the morphological and ecological aspects of a rare, beautiful coastal environment. The Venice Project is presently being carried out by 28 specialized contractors: Consorzio Venezia Nuova (CVN). The basic design was substantially finalized in 1992 and the main works should be completed within 10 years.

The most striking part of the Venice Project is the design and construction of flood control barriers at the three inlets to the lagoon. It is planned to construct four mobile barriers with a series of hollow buoyancy flap-gates (two at Lido inlet, one at Malamocco, one at Chioggia) with an overall length of about 1.7 km. The flap-gates, made of prismatic metal caissons (each 20 m wide), will be hinged to precast concrete foundation caissons, laid along a trench in the seabed in depths of 6 to 15 m. In calm weather, the gates will rest horizontally on the seabed so as not to obstruct normal navigation or to impair the view.