The ‘acqua alta’ phenomenon describes the unusually high peak tides which can occur in the northern Adriatic Sea. These tides result when standard astronomical and geophysical tidal effects combine with the sirocco Mediterranean wind, forcing water into the north-western region of the Adriatic. Because of the particular location of Venice, the distinctive shape of the Venetian Lagoon and the well-documented subsidence of the city in general, flooding in Venice can be particularly severe compared to other coastal Adriatic cities. The highest recorded tide level in Venice took place in on 4th November 1966, when the city was covered by 194cm of saltwater. As recently as 29th October 2018, a 156cm high tide threatened further deterioration and damage to Venice. With high water events increasing in frequency as well as intensity, Venetians were in dire need of a long term solution. The MOSE project was the result.
MOSE (or Modulo Sperimentale Elettromeccanico) is a critical large-scale engineering project, with the intention of protecting the city of Venice and the Venetian Lagoon from flooding. The project is an installation of 78 mobile gates across the three inlets (Lido (1), Malamocco (2) and Chioggia (3), numbered in the image below), between the Venetian Lagoon and the Adriatic Sea. In the event of an impending high tide, the gates can be individually raised or closed according to the conditions. Working alongside many other flood prevention measures, including coastal reinforcement and the raising of quaysides, MOSE will help to protect Venice from future tides of up to three metres in height.
Map of Venetian Lagoon and north-western Adriatic Sea, with locations of inlets marked
When a high tide is forecast, the MOSE gates are raised through the introduction of compressed air and subsequent deplacement of water. This results in the rotation of the gate around its hinge axis, and the gate rising from the sea floor housing to above the water line. With each gate weighing in at 330 tons, and at a total project cost in the region of €6 billion, you would rightfully expect the engineering going on in and around these gates to be of the highest specification. This is where Precision Polymer Engineering comes in.
MOSE gate cross-section: 1. Gate; 2. Hinge; 3. Base of gate; 4. Access tunnels; 5. Land compaction piles
Precision Polymer Engineering (PPE) was selected to develop two distinct sealing geometries for the MOSE project. These geometries made use of PPE’s proprietary high performance Z85L material.
The Z85L grade is an HNBR hydrogenated nitrile, which is specially compounded for long term reliable service in low temperature applications. The high mechanical strength of Z85L provides excellent wear and abrasion resistant properties, particularly when used in dynamic applications. Excellent chemical resistance makes the material ideal for use with all kinds of operating fluids, from sea water through to the most chemically aggressive of industrial lubricants.
PPE not only supplied the original equipment manufacturer with high performance sealing solutions, but owing to our positioning with the MRO provider for the MOSE project, we are also proud to offer our continuous support to MOSE with its ongoing spares demand.
This is just one example of how Precision Polymer Engineering sealing materials have been adopted into major international projects as a result of their proven performance and reliability in harsh operating environments.