In 1981 the Italian government initiated the MOSE project to protect the Venetian lagoon as well as the iconic historic heritage of the city of Venice from flooding. The MOSE project (MOdulo Sperimentale Elettromeccanico or Experimental Electromechanical Module) is an integrated system consisting of rows of mobile flap gates. These gates are installed at the three inlets to the Venetian lagoon at Lido, Malamocco and Chioggia to isolate the lagoon temporarily from the Adriatic Sea during forecasted acqua alta high tides. The Consorzio Venezia Nuova (CVN) is the concessionaire for all the works on behalf of the government and began construction works in 2003.
At the Malamocco inlet a large navigation lock with a length of 380m and a width of 50.5m was constructed. This navigation lock is intended to ensure the accessibility of the Port of Venice during acqua alta, when the flap gates will be closed. Only months after completion of the Malamocco lock, the sea side lock gate suffered severe damage during a storm on the Adriatic Sea on 5th and 6th February 2015. The lock gates were taken out of service and precautionary measures had to be taken by CVN to temporarily stabilize the damaged lock gate. SBE was subsequently involved to investigate the cause of the damage and to propose design solutions.
To explain the physical phenomena that caused the damage to the lock gate, several numerical studies of the wave climate in front of the lock were carried out. It was concluded that the damage was instigated by the combined effect of the specific wave conditions at this location and the particular design concept of the original lock gate. The combination of these effects resulted in significant uplift forces on the ballast tank of the lock gate which eventually led to the observed damage.
Based on these results, it was concluded that both gates of the navigation lock had to be adapted or if necessary entirely redesigned. This paper focuses on the redesign of the sea side lock gate. For this lock gate, various alternative design concepts were developed and their performance under wave action was compared by means of scale model testing. Although the proposed changes resulted in a significant improvement, the vertical uplift forces remained high. In the end, a dual solution was therefore proposed with specific design modifications to reduce the vertical uplift forces on the one hand and with an increased net operational weight of the lock gate on the other hand. As a result, the supporting system of the sea side lock gate inevitably also had to be redesigned and changes to the civil structures will have to be made as well.
At present, the construction works of the new sea side lock gate are underway and the primary line of defense of the MOSE system is expected to be finished by the end of 2019. The Malamocco lock is expected to be operational by March 2020.