From super-sewers to flood barriers, governments worldwide are investing in mega projects to protect cities from powerful storms.

A Rainy Year

The year 2024 may not even be halfway through, but it is already shaping up to be one of the rainiest on record.

In April, Dubai saw a year's worth of rain falling in a single day, turning the international airport into a lake and flooding the metro. In May, Brazil was hit by one of its worst floods ever, which killed 155 people and forced 540,000 to leave their homes.

For governments worldwide, the increasing likelihood of catastrophic storms, combined with rising urbanization rates and the need to replace outdated infrastructure, is driving record investments in super-sewers, flood barriers, and resilience projects.

ConstructionBriefing has analyzed 10 of the most significant projects. Here they are:

New York, USA, Flood Barriers

In response to severe flooding from Hurricane Sandy in 2012, New York City authorities have considered ways to protect the city.

The following year, the U.S. Department of Housing and Urban Development launched Rebuild by Design, a $930 million design competition to make the neighborhoods affected by the hurricane more resilient. Ten of the 150 proposals were selected, and seven received federal grants.

The largest grant, totaling $335 million, went to the "The Big U" proposal by Danish architect Bjarke Ingels Group and others, which includes a 12-kilometer barrier—or berm—around Lower Manhattan, incorporating public spaces and parks designed to retain floodwaters from Manhattan's shores.

One of the largest segments of the Big U was known as the East Side Coastal Resiliency project. According to the initial Big U plan, it included an 8-foot berm along FDR Drive, from East 23rd Street to Montgomery Street.

However, in 2018, following a "value engineering" analysis by the city, Mayor Bill de Blasio announced that instead of building a berm, the entire 57.5-acre East River Park would be elevated. In December 2019, the New York City Council voted to approve a $1.45 billion plan to bury the park under 8 feet of new soil and build a redesigned park on higher ground, so the new park could act as a flood barrier.

Construction began in 2021, after a prolonged legal battle with local residents. IPC Resiliency Partners, a consortium of CAC Industries, Posillico Inc., and Lovino, is currently working on the first phase of the project, scheduled to be completed later in 2024. Perfetto Contracting is working on the second phase. The entire project is scheduled for completion in 2026.

Other segments of the Big U are also underway. Last year, the Battery Park City Authority, the body that administers Battery Park, awarded a $631 million design and construction contract to Turner Construction and its subsidiary EE Cruz for part of a "sea-level resilience project" to build a series of flood barriers around the southern tip of Manhattan.

Separately, in June, the U.S. Army Corps of Engineers awarded a $132.7 million contract to Triumph Construction, based in New York, to build a series of drainage ponds and stormwater infrastructure on Staten Island.

And additional measures could be taken. In 2022, after completing a feasibility study, the U.S. Army Corps of Engineers released a draft plan comprising 2.2 miles of storm barriers, 50.6 miles of levees, and other shoreline-based measures, 11.8 miles of flood-induced mitigation features, and 30.7 miles of risk-reduction features.

USACE estimated that the project would have a total cost in present value of $76.2 billion and an estimated construction duration of 14 years. If the plans are approved by New York and New Jersey officials and Congress—and funding is approved—construction could start as soon as 2030.

Strategic Sewer Tunnel Project in Dubai, Dubai, UAE

In February 2024, the Dubai government invited contractors to bid for an $80 billion AED (USD 22 billion) sewer tunnel project, which will be developed as a public-private partnership.

The project includes the construction of two sets of deep tunnels ending at two pumping stations located at the wastewater treatment plants in Warsan and Jebel Ali.

A conventional sewer and drainage system and treatment plants will be built in Hatta. It also includes recycled water distribution systems connected to treatment plants.

The project follows the 12.5 billion AED (USD 3.4 billion) deep tunnel drainage project, which spans 75 kilometers and is up to 90 meters deep, completed in 2021 by the U.S.-based Parsons, and is part of a system designed to collect and store rainwater for the next 100 years.

MOSE, Venice, Italy

The MOSE mobile flood barrier in Venice is actually a series of four barriers formed by rows of mobile gates installed on the seabed at the Lido, Malamocco, and Chioggia inlets, which can be raised to temporarily isolate the Venice Lagoon from the ocean during storms.

The project was first subcontracted by the Italian government in 1984 to Consorzio Venezia Nuova, a consortium of major Italian companies. However, construction of the megaproject did not begin until 2003 and has been plagued by delays, cost overruns, and corruption allegations.

The barriers were successfully raised for the first time in 2020 and were expected to be completed in 2021, but recent documents published in the Italian newspaper Il Fatto Quotidiano now say that interventions made possible by new funding push the completion date to December 2025. The total project cost has been estimated at 6 billion euros (USD 6.5 billion).

West Shore Lake Pontchartrain, Louisiana, USA

The West Shore Lake Pontchartrain project, located in southeast Louisiana on the east bank of the Mississippi River, comprises 17.5 miles of levees, one mile of concrete floodwalls, pumping stations, drainage structures, and other non-structural protection measures coordinated by the U.S. Army Corps of Engineers, New Orleans District, extending from Bonnet Carre Spillway to the Mississippi River Levee near Garyville.

The project, with an estimated cost of USD 760 million, is designed to provide storm protection for 60,000 residents in St. Charles, St. James, and St. John the Baptist parishes. Contracts for various construction packages within the project have been awarded to Louisiana-based companies, including: Material Onshore; Mandeville Construction, Dynamic Group, EvCo Development, and Lemoine-Frazier.

Construction began in December 2022 and is expected to be completed in 2027.

Potomac River Tunnel, Washington DC, USA

A joint venture between CBNA, a U.S. subsidiary of French contractor Bouygues Construction, and Halamar International, supported by engineers COWI and Hatch, began work in February on an $819 million sewer and stormwater channel aimed at reducing the number of sewage overflows into the Potomac River in Washington DC.

The 5.5-mile (8.9 km) main tunnel will run under the Potomac River in Washington DC and connect to the existing Anacostia River tunnel, storing stormwater and effluents and transporting them to the Blue Plains Advanced Wastewater Treatment Plant.

The 100-foot (30 m) deep tunnel will have an interior diameter of 18 feet (5.5 meters) and will traverse variable geologic conditions (clay, alluvium, hard rock) passing close to iconic Washington DC monuments.

It will require the use of two custom-built tunnel boring machines for these soil conditions. Work on the project is expected to be completed by 2030.

Thames Tideway Tunnel, London, UK

Completed in March after eight years of construction, the £5 billion (USD 6.4 billion) Thames Tideway Tunnel is the largest infrastructure project ever undertaken by the UK water industry.

The 16-mile (26-kilometer) and 7.2-meter wide tunnel, running from Acton in West London to Abbey Mills in East London, will divert 34 of the most polluting sewer overflows that have spilled into the Thames and store them in the tunnel until they can be processed.

The first sewer is expected to flow into the new tunnel this summer and should be fully operational by 2025. Contractors involved in the project included: BAM Nuttall, Morgan Sindall, Balfour Beatty, Ferrovial Agroman, Laing O'Rourke, Costain, Vinci, and Bachy Soletanche.

Clearwater Project, Los Angeles

After a multi-year assessment of the Los Angeles County Sanitation Districts' main sewer system, which serves over 5 million people, the districts agreed to build a 7-mile long and 18-foot diameter tunnel to transport treated water from the Joint Water Pollution Control Plant in Carson to existing ocean outfalls at Royal Palms Beach in San Pedro.

In 2019, the districts awarded a $630 million construction contract to Dragados USA, the American subsidiary of Spanish contractor Dragados. The project is scheduled for completion in 2026.

Mill Creek Drainage Relief Tunnel, Dallas, USA

The Mill Creek Drainage Relief Tunnel, set to be completed in 2026, is a five-mile underground tunnel stretching from the State Thomas District in uptown Dallas, through Mill Creek, and Peaks Branch.

The 30-foot-diameter tunnel that sits 70 to 100 feet underground is designed to protect nearly 6,000 residential and commercial properties in the east Dallas area from flooding for the next century.

The project is being built by Southland Mole, a joint venture of two Texas-based Southland Holding subsidiaries, which was awarded the $206.7 million construction contract in 2018. A Robbins Beam Beam tunnel boring machine was used to drill through the chalk Austin between spring 2020 and summer 2022, and a concrete liner is added by 2025.

Cloudburst Tunnels, Copenhagen, Denmark

Following a huge cloudburst in Copenhagen in 2011, Copenhagen City Hall identified the need for a new sewerage and stormwater network that could direct runoff from the city's cloudbursts into the Oresund Strait.

As a result, the municipality developed a Cloudburst Management Plan to build two new stormwater drainage tunnels that it describes as "water highways." The Kalvebod Brygge tunnel is 1,360 meters long, while the Valby tunnel is 1,500 meters long.

The tunnels measure up to 3 meters in diameter and are located between 12 and 20 meters below sea level. Danish engineering company NIRAS started work on the project as a consultant in 2017.

Tunneling for the Kalvebod Brygge tunnel, using a tunnel, was completed at the end of 2023. The pumping stations are expected to be operational in 2026.

At the end of May this year, a joint venture between Danish contractor MT Højgaard Danmark and French company Eiffage won the contract to build the 2,380 m long Valby tunnel in a contract worth DKK 490 million (US$71.3 million). .

Ring road no. 7 Underground multi-basin regulating tank, Tokyo, Japan

Tokyo already boasts the largest groundwater infrastructure in the world, comprising 28 underground regulating reservoirs on twelve rivers with a total storage volume of 2.63 million cubic meters.

However, after dramatic increases in the intensity and frequency of storms, the Tokyo Metropolitan Government Construction Board allocated an additional ¥6.6 billion (US$42 million) to enhance flood defenses in the metropolitan area .

In 2022, work began on a 5.4 km long, 13.2 meter diameter tunnel-shaped reservoir with a capacity of 1.4 million cubic meters, connecting the existing underground reservoirs of the Kanda River and the Shirako River . Construction is expected to be completed in 2026. (Photo: Freepik)