MOSE is a system of mobile barriers designed to protect the city of Venice from the phenomenon of the “acqua alta” high tides. The mobile barriers consist of rows of gates hinged to self-sinking caissons aligned on the sea bottom at the entrance to each of the three lagoon inlets (Lido, Malamocco, Chioggia) that link the sea to the lagoon. Under normal tidal conditions, the gates are full of water and rest in the caissons housed on the bottom of the inlets from the sea to the lagoon. But when sea level exceeds 100 cm, the gates are brought to the surface by an air injection system. This mechanism makes it possible to temporarily isolate the lagoon from the sea, thus blocking the effects of the tidal flow.
The Lido inlet was divided into two parts by creating an artificial island. Astaldi worked in carrying out the interventions in the northern part (Lido-Treporti inlet), where the design calls for 21 mobile gates, each of which 18.55 metres long and 20 metres wide, with a thickness of about 4 metres. The gates are attached to 7 housing caissons, which are concrete structures placed on the sea bottom. The housing caissons are 36 metres wide and 60 metres long, with a height of just under 9 metres; each caisson holds 3 gates. The intervention for the Lido-Treporti inlet calls for creating a small craft harbour to guarantee that the inlet can be navigated even when the gates are raised. This harbour, sealed and drained, has been set up as a temporary work site area for the construction of the nine caissons. At the end of this construction phase, the basin was flooded with water and the caissons, one at a time, were floated along the inlet, sunk, and ballasted in the excavation made in the sea bottom.
