MARÍA GÓMEZ BRAVO | Tungsteno
On November 4, 1966, the acqua alta in Venice reached 1.94 meters, the highest level recorded in the city since systematic measurements began. The rising tide inundated streets, homes, shops, and historic buildings. That flood marked a turning point in the protection of the Venice Lagoon and set in motion a process that, decades later, led to the MOSE system: 78 movable floodgates designed to temporarily isolate Venice from the Adriatic Sea when exceptionally high tides threaten to overwhelm the city.
Venice is not an isolated case. More and more cities are turning to infrastructure that is activated only when the risk exceeds certain thresholds. Many of these systems were developed using historical records that made it possible to estimate the probability of floods, storms, or exceptionally high water levels with reasonable accuracy. Rising sea levels and the increasing intensity of some extreme weather events are now altering those reference points. The latest IPCC (Intergovernmental Panel on Climate Change) report warns that the risk of coastal and river flooding will increase during this century—a trend that calls for a reassessment of both existing infrastructure and the criteria used to design new urban flood defense systems.
Barriers Lying in Wait Beneath the Sea
St. Mark’s Square submerged under water will remain a familiar sight in Venice. For now, however, the MOSE system remains inactive most of the time. The flood-control system is activated only when forecasts predict an exceptionally high tide capable of flooding the city. When that happens, the barriers rise from the bottom of the lagoon to block the sea from entering. Once the danger has passed, they sink back beneath the water.
The MOSE system’s movable gates temporarily isolate the Venice Lagoon from the Adriatic Sea when the tide rises to approximately one meter. Credit: VINCENZO PINTO/AFP via Getty Images
Since becoming operational in 2020, the system has protected Venice from several episodes of acqua alta that would otherwise have flooded much of the historic center. Yet its implementation has not put an end to the debate over the lagoon’s future. In fact, a study published last year by researchers at Italy’s Istituto Nazionale di Geofisica e Vulcanologia (INGV) suggests that rising sea levels, combined with the gradual subsidence of the land on which the lagoon sits, will likely require the MOSE system to be activated more frequently over the course of this century.
Protecting Venice is no longer simply a matter of keeping the water out. The challenge extends beyond raising the barriers when floodwaters threaten the city. It is about doing so in a way that preserves the lagoon that has shaped Venice’s identity for centuries.
London: Learning to Adapt Infrastructure
The 1953 North Sea storm surge changed the way the United Kingdom understood flood risk. The storm and the resulting flooding claimed the lives of hundreds of people along England’s east coast and exposed London’s vulnerability to extreme weather events. Three decades later, the Thames Barrier became operational.
The Thames Barrier is one of the key components of the Thames Estuary Plan 2100, the strategy to adapt the estuary to rising sea levels and reduce the risk of flooding. Credit: Tim Motion/Construction Photography/Avalon/Getty Images
Today, the Thames Barrier remains the cornerstone of London’s flood protection system, but the challenge is no longer simply to operate the barrier—it is to determine when it will no longer be sufficient. The Thames Estuary 2100 project, led by the UK Environment Agency, reassesses the estuary’s evolution and climate projections every five years to determine when to reinforce dikes, raise flood walls, or adapt existing defenses. Rather than a completed project, protecting the estuary has become an ongoing process of adaptation, driven by changes in both the climate and the infrastructure itself.
Rotterdam: Protection Without Halting Activity
While the United Kingdom responded to the 1953 storm surge disaster by building the Thames Barrier, the same storm also caused catastrophic flooding in the Netherlands, prompting the creation of the National Delta Program, one of the world’s largest hydraulic engineering initiatives. The Maeslantkering (Maeslant Barrier), inaugurated in 1997 at the entrance to the Port of Rotterdam, was the final major component of that program. It was designed to solve a problem that the massive dikes built decades earlier could not: protecting the coastline without blocking access to Europe’s largest port.
Its two steel arms, each 237 meters long, remain open to allow ships to pass and close only when hydrological and meteorological models predict sea levels high enough to threaten the safety of the estuary. The decision is made automatically, although it remains under the supervision of Rijkswaterstaat, the Dutch agency responsible for water management and national infrastructure. To make that decision, the system relies on a network of sensors, measuring stations, and numerical models that integrate data on sea level, wind, waves, and river flow to anticipate the progression of each storm.
The Maeslant Barrier’s closure system is fully automated and controlled by a centralized decision-support system called Beheerscentrale (BOS). Source: Rijkswaterstaat7u
The barrier was designed to be activated only a few times each year. The rest of the time, it remains open and the port operates normally. This approach reflects a broader shift in hydraulic engineering: infrastructure is no longer kept active at all times but is instead activated only when the level of risk demands it.
Diverting Water Beneath the City
Containing the sea is only part of the challenge. Extreme rainfall can cause rivers to overflow and overwhelm urban drainage systems in a matter of hours. Tokyo chose to tackle this risk underground. Recurring floods caused by typhoons and torrential rains in the Tokyo metropolitan area led Japan to develop the G-Cans system, an underground complex designed to divert excess water.
At a depth of about 50 meters, a 6.3-kilometer network of tunnels connects several waterways, diverting excess water into the Edo River. The system began operating in 2002 and has since become one of the primary defenses for northern Tokyo, as well as an unexpected tourist attraction. During Typhoon Hagibis in 2019, it diverted more than 12 million cubic meters of water and reduced the number of flooded homes in the Nakagawa and Ayase river basins by about 90 percent, according to Japan’s Ministry of Land, Infrastructure, Transport, and Tourism. Unlike coastal barriers, it does not prevent water from entering the system; instead, it redirects and channels the water along a controlled route.
G-Cans, the world’s largest underground flood control system, diverts excess water into the Edo River to protect the Tokyo metropolitan area. Credit: John S Lander/LightRocket via Getty Images
Kuala Lumpur took the concept a step further. The SMART Tunnel, which opened in 2007, combines two types of infrastructure into a single structure: an urban highway and a flood-drainage tunnel. When heavy rainfall threatens to cause the rivers in the Malaysian capital to overflow, traffic is halted, the tunnel is closed to vehicles, and it becomes part of the city’s flood-control system. Once the floodwaters recede, the tunnel is cleaned and reopened to traffic. Rather than trying to hold back water at all costs, modern engineering increasingly seeks to redirect its flow, minimizing its impact on the city.
From Containing the River to Giving It Space
Sometimes, the most effective engineering solution is not to contain a river, but to give it back some of the space it once occupied. The Dutch Room for the River program was developed around this principle. The Rhine and Meuse floods of 1993 and 1995, which forced the evacuation of some 250,000 people, exposed the limitations of continually raising river defenses while the space available to the rivers continued to shrink.
The program transformed more than 30 river sections by moving dikes inland, creating secondary channels, and restoring areas that can temporarily store floodwaters. According to a study published in the journal Geosciences, this approach reduces pressure on the dikes and mitigates the impacts of flooding. Rather than replacing existing flood defenses, it complements them by making the river itself part of the solution.
None of these interventions completely eliminates flood risk. Instead, they are based on the recognition that flooding will continue to occur and that the most effective protection comes from systems capable of adapting to changing conditions. The rigid concrete solutions and static calculations of the past have given way to infrastructure designed to manage uncertainty. The paradox of these systems is that their greatest success is measured by what does not happen: an extreme weather event passes without disrupting the city’s daily life, becoming just another entry in the hydrological record.
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