The MOSE project will provide flood protection through installation of 78 mobile barriers at the Lido San Nicolò, Malamocco, and Chioggia (shown here) inlets, the gaps through which the tide enters the Venetian Lagoon.
Sea levels are rising at an increasing rate, resulting in high tides and land subsidence, increasing the incidence of flooding. The global average sea level rose by nearly 7 inches during the last 100 years and it is projected to rise by as much as 48 inches by 2100. Eleven of the world’s 15 largest cities, including New York, Tokyo, and Mumbai, lie along coasts, so this will have a dramatic impact on a large portion of the world’s population and the world’s economy. In fact, the number of people affected by floods is expected to triple to 54 million in less than 15 years, so the need to act now and to prioritize flood prevention schemes is apparent.
Half the world’s population — 3.7 billion people — now reside in cities. There is a continuing global shift toward urbanization with 77 million people migrating from rural to urban areas each year with significant implications for water infrastructure and management. Megacities, with their populations of more than 10 million, are a growing phenomenon, doubling to 29 throughout the world in the last two decades. These megacities place massive demands on flood management schemes, which is illustrated by the concentrated growth of South East Asian megacities in flood-prone areas.
With annual losses from flooding in the world’s biggest coastal cities expected to rise from $6 billion a year currently to more than $1 trillion by 2050, doing nothing is no longer an option. Flood management programs need to take into account the effects of changing weather patterns, such as the trend toward heavy, intense rainfall that is already being experienced in the U.S.
Case study: Protecting Venice
One city already safeguarding its future with significant investment in its flood defense is arguably the world’s most iconic “water city,” Venice. This is due to the fact that the city — which consists of 118 small islands connected by numerous canals and bridges — is prone to flooding caused by ever-rising tides.
To protect Venice, the Venetian Lagoon and its neighboring cities required an ambitious and iconic storm surge solution. The MOSE project will provide flood protection through installation of 78 mobile barriers at the Lido San Nicolò, Malamocco, and Chioggia inlets, the gaps through which the tide enters the lagoon. These surge barriers will be activated when the tide reaches 110 centimeters inside the 500-square-kilometer Venetian Lagoon, effectively separating it from the Adriatic Sea to prevent flooding. The total cost of the project is estimated to be €5.5 billion, with completion in 2018.
The flood defense scheme’s 78 mobile flood gates can be raised at high tide to create four temporary flood barriers at three points. At the Lido inlet, the widest point, two rows of gates made up of 21 and 20 barriers, respectively, are linked by an artificial island that houses the technical buildings and the system operating plant. The smaller Malamocco inlet has one row of 19 gates and there are 18 at the Chioggia inlet. The gates are connected to concrete housing structures with hinges, the technological heart of the system that allows them to move.
When not in use, the gates rest on special housings at the bottom of the lagoon, completely out of sight. Sourcing a reliable sealing system that would stand the test of time and support the long-term integrity of the structure was therefore a key consideration.
A high-performance gasket, manufactured from a blend of styrene-butadiene rubber (SBR) and natural rubber due to the material’s high resilience in case of seismic activity, will be mounted on each of the 78 gates, acting as a dynamic seal to ensure watertight protection. Often used to provide a seal between two concrete segments or for sealing temporary bulkheads at the end of tunnels, the gasket was the preferred sealing solution as it is able to withstand very high hydrostatic pressures.
With the barrier infrastructure submerged, it is vital that a secondary seal will then be clamped across the sectional elements of the mobile barriers. A seal consisting of two nylon plies with SBR cover on the inside and outside will be used to withstand high water pressure and allow for axial and radial movements and/or rotation of the gates.
Ensuring the right solution
Water infrastructure is required in increasingly challenging environments. Therefore, it is vital that those involved with such high-stake projects closely collaborate with a manufacturer at an early stage to ensure the most appropriate and fully reliable water infrastructure management solution is engineered.
Advanced modelling and testing are a key part of this process. From best practice design, manufacture, and testing to full in-life support, leading manufacturers can develop solutions that deliver long-term stability through an improved ability to handle movement and aging, and better resistance against temperature and chemical erosion. This also reduces the need for maintenance, an increasingly important criteria given the remoteness of some infrastructure.
Watch a video about the MOSE project at https://www.youtube.com/watch?v=jO8tVOhRHr4&feature=youtu.be.
Information provided by Trelleborg Engineered Products (www.trelleborg.com/en/engineered-products).