MOSE
The project is an integrated system consisting of rows of mobile gates, installed on the seafloor at the Lido, Malamocco, and Chioggia inlets, that can be raised to temporarily seal off the Venetian Lagoon from the Adriatic Sea during acqua alta high tides. Together with other measures, such as coastal reinforcement, elevating of quaysides, and paving and improvement of the lagoon, MOSE is designed to protect Venice and the lagoon from tides of up to 3 metres (9.8 ft). As of 2023, the floodgates are raised for tides forecast to be more than 1.30 metres (4 ft 3 in).
The Consorzio Venezia Nuova is responsible for the work on behalf of the Ministry of Infrastructure and Transport – Venice Water Authority. Construction began simultaneously in 2003. On 10 July 2020, the first full test was successfully completed, and after multiple delays, cost overruns, and scandals resulted in the project missing both its 2018 completion deadline (originally a 2011 deadline) and its 2021 deadline, and is now to be finished in 2025. On 3 October 2020, the MOSE was activated for the first time in the occurrence of a high tide event, preventing some of the low-lying parts of the city (in particular piazza San Marco) from being flooded. In 2020, the experts who had conceived a set of three floodgates separating the Adriatic Sea from Venice estimated that each year they would have to raise the floodgates 5 times. Within two years after the inaugural raising of the floodgates, MOSE was activated 49 times.
Origin of the name
Before the acronym was used to describe the entire flood protection system, MOSE referred to the 1:1 scale prototype of a gate that had been tested between 1988 and 1992 at the Lido inlet.
The name also holds a secondary meaning: "MOSE" alludes to the biblical character Moses ("Mosè" in Italian), who is remembered for parting the Red Sea.
Context
MOSE is part of a General Plan of Interventions to safeguard Venice and the lagoon. The project was begun in 1987 by the Ministry of Infrastructure through the Venice Water Authority (the Ministry's operational arm in the lagoon) and the concessionary Consorzio Venezia Nuova. The measures already completed or underway along the coastline and in the lagoon are the most important environmental defense, restoration, and improvement program ever implemented by the Italian State.
In parallel with the construction of MOSE, the Venice Water Authority and Venice Local Authority are raising quaysides and paving in the city in order to protect built-up areas in the lagoon from medium high tides (below 110 centimetres (43 in), the height at which the mobile barriers will come into operation). These measures are extremely complex, particularly in urban settings such as Venice and Chioggia where the raising must take account of the delicate architectural and monumental context. Measures to improve the shallow lagoon environment are aimed at slowing degradation of the morphological structures caused by subsidence, eustatism, and erosion due to waves and wash. Work is underway throughout the lagoon basin to protect, reconstruct, and renaturalise salt marshes, mud flats and shallows; restore the environment of the smaller islands; and dredge lagoon canals and channels.
Important activities are also underway to redress pollution in the industrial area of Porto Marghera, at the edge of the central lagoon. Islands formerly used as rubbish dumps are being secured while industrial canals are being consolidated and sealed after removal of their polluted sediments.
Baby MOSE
'Baby MOSE' is the flood defence system protecting Chioggia from the most frequently occurring high waters, up to a maximum of 130 cm.
Completed in the summer of 2012, it consists of two movable sluices located at the ends of the Vena canal - the canal that crosses the centre of Chioggia from North to South. These can be raised in a few minutes and protect the center of Chioggia from the most frequent high waters.
The two sluices (Vigo and Santa Maria) are equal, 18 m long, 3.3 wide and 80 cm thick; in case of threatening tides, they are raised in eight minutes using hydraulic motors.
Together with raising canal banks and the areas at the edge of the urban centre, completed previously, the babyMose is able to defend from tides up to 130 cm.
The babyMose was completed in time to keep the center of Chioggia dry during the high water of October 2012.
In the case of more extreme high waters, it is necessary to wait for the main MOSE to come into operation, which blocks the entrance of the tide into the lagoon through the closure of the MOSE barriers.
The babyMose, as well as the other interventions of protection and urban redevelopment implemented in Chioggia in recent years, was carried out by the Magistrate of the Waters of Venice, through the Consorzio Venezia Nuova, together with the municipal administration.
Objectives
The aim of MOSE is to protect the lagoon, its towns, villages, and inhabitants along with its iconic historic, artistic, and environmental heritage from floods, including extreme events. Although the tide in the lagoon basin is lower than in other areas of the world (where it may reach as high as 20 metres (66 ft)), the phenomenon may become significant when associated with atmospheric and meteorological factors such as low pressure and the bora, a north-easterly wind coming from Trieste, or the Sirocco, a hot south-easterly wind. Those conditions push waves into the gulf of Venice. High water is also worsened by rain and water flowing into the lagoon from the drainage basin at 36 inflow points associated with small rivers and canals.
Floods have caused damage since ancient times and have become ever more frequent and intense as a result of the combined effect of eustatism (a rise in sea level) and subsidence (a drop in land level) caused by natural and man-induced phenomena. Today, towns and villages in the lagoon are an average of 23 centimetres (9.1 in) lower with respect to the water level than at the beginning of the 1900s and each year, thousands of floods cause serious problems for the inhabitants as well as deterioration of architecture, urban structures and the ecosystem. Over the entire lagoon area, there is also a constant risk of an extreme catastrophic event such as that of 4 November 1966 (the great flood) when a tide of 194 centimetres (76 in) submerged Venice, Chioggia and the other built-up areas. Floods effects are exacerbated due to greater erosion by the sea caused by human interventions to facilitate port activities (e.g. through the construction of jetties and artificial canals); establishment of the industrial Porto Marghera area; and increased wash from motorized boats, which all aggravate erosion of morphological structures and the foundations of quaysides and buildings. In the future, the high water phenomenon may be further aggravated by the predicted rise in sea level as a result of global warming.
In this context, MOSE, together with reinforcement of the barrier island, has been designed to provide protection from tides of up to 3 metres (9.8 ft) in height. The aim of MOSE is to protect the lagoon, even if the most pessimistic hypotheses are proven true, such as a rise in sea level of at least 60 centimetres (24 in). However, the reports have grown more pessimistic with time compared to when MOSE was originally planned; the 2019 estimate from the IPCC (Intergovernmental Panel on Climate Change) predicts a rise in sea level of between 60 and 110 centimetres (24 and 43 in) by 2100 if emissions continue to increase, which MOSE was not designed to handle.
MOSE is flexible and can be operated in different ways according to the characteristics and height of the tide. Given that the gates are independent and can be operated separately, all three inlets can be closed in the case of an exceptional event, the inlets can be closed one at a time according to the winds, atmospheric pressure and height of tide forecast, or again, each inlet can be partially closed.
Exceptionally high waters have struck the city since 1935: levels of 140 cm or greater have been recorded during the following floods, with 12 of the 20 events occurring in the 21st century:
| Date | Height |
|---|---|
| 22 November 2022 | 2.04 metres (6 ft 8 in) |
| 4 November 1966 | 1.94 metres (6 ft 4 in) |
| 12 November 2019 | 1.87 metres (6 ft 2 in) |
| 22 December 1979 | 1.66 metres (5 ft 5 in) |
| 1 February 1986 | 1.59 metres (5 ft 3 in) |
| 29 October 2018 | 1.56 metres (5 ft 1 in) |
| 1 December 2008 | 1.56 metres (5 ft 1 in) |
| 15 November 2019 | 1.54 metres (5 ft 1 in) |
| 15 November 1951 | 1.51 metres (4 ft 11 in) |
| 11 November 2012 | 1.49 metres (4 ft 11 in) |
| 16 April 1936 | 1.47 metres (4 ft 10 in) |
| 16 November 2002 | 1.47 metres (4 ft 10 in) |
| 25 December 2009 | 1.45 metres (4 ft 9 in) |
| 15 October 1960 | 1.45 metres (4 ft 9 in) |
| 13 November 2019 | 1.44 metres (4 ft 9 in) |
| 23 December 2009 | 1.44 metres (4 ft 9 in) |
| 6 November 2000 | 1.44 metres (4 ft 9 in) |
| 12 February 2013 | 1.43 metres (4 ft 8 in) |
| 1 November 2012 | 1.43 metres (4 ft 8 in) |
| 8 December 1992 | 1.42 metres (4 ft 8 in) |
| 17 February 1979 | 1.40 metres (4 ft 7 in) |
Prior to 1936, the highest levels had been in 1879, when on 25 February the water reached 137.5 cm, and on 21 November 1916, when a level of 136 cm occurred. Since 1936, there have been 17 occasions when the level reached between 130 and 140 cm.
All values were recorded at the monitoring station at Punta della Salute (Punta della Dogana) and refer to the 1897 tidal datum point.
The highest tide in over five decades on 13 November 2019 left 85% of the city flooded. Mayor Luigi Brugnaro blamed the situation on climate change. A Washington Post report provided a more thorough analysis:
"The sea level has been rising even more rapidly in Venice than in other parts of the world. At the same time, the city is sinking, the result of tectonic plates shifting below the Italian coast. Those factors together, along with the more frequent extreme weather events associated with climate change, contribute to floods."
Operating principles
MOSE consists of rows of mobile gates on the seabed at the three inlets that can be raised to temporarily seal off the lagoon from the sea during high tide. There are 78 gates grouped into four barrier rows. At the Lido inlet, the widest, there are two barrier rows of 21 and 20 gates, respectively, linked by an artificial island (the island connecting the two rows of gates at the centre of the Lido inlet also accommodates the technical buildings housing the system operating plant). In addition, there is one row of 19 gates at the Malamocco inlet and one row of 18 gates at the Chioggia inlet.
The gates consist of metal box-type structures 20 metres (66 ft) wide for all rows, with a length varying between 18.5 and 29 metres (61 and 95 ft) and from 3.6 to 5 metres (12 to 16 ft) thick. The gates are connected to the concrete housing structures with hinges, the technological heart of the system, which allow the gates to move while attached to the housing structures on the seafloor.
Under normal tidal conditions, the gates are full of water and rest in their housing structures. When a high tide is forecast, compressed air is introduced into the gates to empty them of water, causing them to rotate around the axis of the hinges and rise up until they emerge above the water to stop the tide from entering the lagoon. When the tide recedes, the gates are filled with water again and lowered into their housing.
The inlets are closed for an average of between four and five hours, including the time taken for the gates to be raised (about 30 minutes) and lowered (about 15 minutes).
To guarantee navigation and avoid interruption of activities in the Port of Venice, when the mobile barriers are in operation, a main lock is constructed at the Malamocco inlet to allow the transit of large ships; while at the Lido and Chioggia inlets, there are smaller locks to allow emergency vessels, fishing boats and pleasure craft to shelter and transit.
Operating procedure dictates that the gates will be raised for tides of more than 110 centimetres (43 in) high. The authorities have established this as the optimum height with respect to current sea levels, but the gates can be operated for any level of tide. The MOSE system is flexible: depending on the winds, atmospheric pressure and level of tide, it can oppose the high water in different ways – with simultaneous closure of all three inlets in the case of exceptional tides, by closing just one inlet at a time, or by partially closing each inlet—given that the gates are independent—for medium-high tides.
Chronology
Following the flood of 4 November 1966 when Venice, Chioggia and the other built-up areas in the lagoon were submerged by a tide of 194 centimetres (76 in), the first Special Law for Venice declared the problem of safeguarding the city to be of "priority national interest". This marked the beginning of a long legislative and technical process to guarantee Venice and the lagoon an effective sea defence system.
To this end, in 1975 the State Ministry of Public Works issued a competitive tender, but the process ended without a project being chosen from those presented as no hypothesis for action satisfied all the mandated requirements. The Ministry subsequently acquired documents presented during the call for tender and passed them to a group of experts commissioned to draw up a project to preserve the hydraulic balance of the lagoon and protect Venice from floods (the "Progettone" of 1981).
A few years later, a further Special Law (Law no. 798/1984) emphasised the need for a unified approach to safeguarding measures, set up a committee for policy, coordination and control of these activities (the "Comitatone", chaired by the President of the Council of Ministers and consisting of representatives of the competent national and local authorities and institutions) and entrusted design and implementation to a single body, the Consorzio Venezia Nuova, recognising its ability to manage the safeguarding activities as a whole. The Venice Water Authority – Consorzio Venezia Nuova presented a complex system of interventions to safeguard Venice (the REA "Riequilibrio E Ambiente", "Rebalancing and the Environment" Project), which included mobile barriers at the inlets to regulate tides in the lagoon. In this context, between 1988 and 1992, experiments were carried out on a prototype gate (MOdulo Sperimentale Elettromeccanico, hence the name MOSE) and in 1989, a conceptual design for the mobile barriers was drawn up. This was completed in 1992 and subsequently approved by the Higher Council of Public Works then subjected to an Environmental Impact Assessment procedure and further developed as requested by the Comitatone. In 2002 the final design was presented and on 3 April 2003, the Comitatone gave the go-ahead for its implementation. The same year, construction sites opened at the three lagoon inlets of Lido, Malamocco and Chioggia.
