There are no climate change scenarios that predict lower sea levels. We seem to have three broadly defined options: Reducing greenhouse gas emissions to minimize sea level rise, building infrastructure to resist rising seas, or waiting for the disasters to occur and rebuilding or relocating afterwards. Any of the three will be expensive, but each calls for a different kind of investment, and might entail different levels of human suffering. The one option we don’t have is thinking it won’t happen.
How much sea levels will rise, and how quickly, depends on what we do about greenhouse gas emissions. This table summarizes the findings from the most recent science assessment from the Intergovernmental Panel on Climate Change (IPCC) in terms of approximate sea level rise for the highest and lowest emissions scenarios for both 2100 and 2300. This table includes the impact of an unlikely but not impossible collapse of major ice caps in Greenland and Antarctica by 2300 (Extreme scenario). A recent paper in Nature communications has expressed human impacts in terms of current populations living in areas that will be permanently drowned or at least seasonally flooded. Many other analyses along these lines are available.
So we can’t say we haven’t been warned, but in keeping with the goals of this Substack site, the focus here is not on perceptions and politics. The focus is on three cases where engineering marvels have been completed to protect older, historic cities that have faced recurring flooding for centuries. Curiosity about how these systems work, and how well they work, as well as how long they took to complete and how much they cost, is what triggered this essay. What might they tell us about hardening other coastal communities against rising seas?
So - a tale of four cities.
St. Petersburg - I was surprised to learn recently that this jewel of Russian history and culture has been prone to flooding from the Gulf of Finland since it was first founded. Peter the Great, seeking a year-round port on the Baltic, ousted earlier Finnic settlers and established the Peter and Paul Fortress in 1703. A first major flood washed away building materials for the fort while still under construction. Since then, the city has been hit almost annually with significant floods; a total of more than 300.
Flooding in this city occurs when storms in the North Atlantic drive sea water into the constricting and land-locked Baltic, and then on into the Gulf of Finland. As the gulf narrows towards St Petersburg, storm surges are focused and accentuated, flooding this city at the eastern end of the Gulf. Much of the city, constructed on a series of low-lying, marshy islands, lies less than 4 meters above current sea level.
An effort to harden the city against further storm surges entailed the construction of a 25 kilometer long system of dams, tunnels and bridges that can isolate the city from the Gulf during storms. The system has two major passages, one north and one south of Kotlin island. Flow through the two openings can be cut off in 45 minutes by the closure of two pairs of enormous curved steel gates weighing 3,000 tons each (like the Dutch system pictured below). These are “floated” by flooding the dry docks in which they are stored, and rotated into place by tractors with 28 sets of wheels. Internal compartments in the gates are then flooded so that the gates sink to the sea floor. The gates must be opened within 48 hours to prevent flooding behind the gates by inflow of the River Neva through the city.
Begun in 1978, construction stalled during the demise of the Soviet Union and was resumed in 2005. The system was commissioned in 2011 and has been activated more than a dozen times since, preventing serious flooding in each case. The project is estimated to have cost $3.85 billion, and is designed to resist storm surges of as much as 5 meters.
Amsterdam and Rotterdam – The Dutch have been winning the battle with the ocean for centuries.
The history of flooding in the “low countries” (the Netherlands) reaches at least as far back as 1287, and the first effort to create new lands (called “polders”) by protecting and draining areas below sea level can be traced to the 11th century.
A few numbers tell the story of both the success of this battle with the sea, and the need to protect what has been won. The long history of reclamation of coastal wetlands in the Netherlands includes the formation of about 3,000 polders. Nearly 17% of the land area of the country has been reclaimed from the sea, and 50% lies less than one meter above current sea level. About 26% of land area is below the current sea level and is home to 21% of the population.
Two overarching projects describe the most recent major reclamation and protection efforts. In the north, the Zuiderzee Works have focused on the area around Amsterdam. In the south, protecting the key port city of Rotterdam has been a main goal of the Delta Works program.
A major step in the Zuiderzee Works project was the construction of a large dike (Afsluitdijk) across the saltwater Wadden Sea in 1932, creating the freshwater Lake Ijssel. The dike shields Amsterdam from storm surges from the North Sea, and has allowed creation of more than 1600 square kilometers (620 square miles) of new land (the polders), most of which has been dedicated to agriculture.
Additional barriers and stations for both releasing and pumping water to the Wadden Sea have been built, and a sophisticated system for optimizing freshwater management for both urban water supply and irrigation of crops is in place. Keeping areas below sea level dry requires constant pumping of water out into the Wadden Sea. Currently two pumping stations with a total of 6 pumps can move 253 cubic meters of water per second. Developing sustainable energy sources to drive these pumps is an active area of engineering and research.
The extent and technical sophistication of this project has led the American Society of Civil Engineers to declare it one of the seven wonders of the modern world.
One of the largest individual efforts in the Delta Works program in the south of the country is the storm surge barrier named the Maeslantkering designed to protect the major port of Rotterdam. Similar in design to the system protecting St. Petersburg, the Dutch version includes two 210 meter long gates weighing 6,800 tons each that are “floated” and swung closed as needed. The gate took 6 years to build at a cost of 635 million Euros.
The barrier was first closed during a storm in November of 2007. With the additional closure of other pre-existing storm barriers, it was reported that the entire Dutch coast was protected from storm surge for the first time.
Sea barriers here and throughout the Netherlands are tested regularly against the standard of a once-in-10,000 year flood. The meaning of this standard is being re-evaluated in light of increasing sea levels.
A recent innovative addition to the Dutch portfolio of preparedness and response is called Room for the River. This identifies locations that can be allowed to flood rather than being totally protected from flooding, reducing somewhat the need to restrain short-term increases in water depth.
Venice – I am a great fan of the books of Donna Leone, all set in and around Venice. The city is a de facto character in each novel, and one, “Acqua Alta,” revolves around the recurring “high water” episodes that have threatened the historical and artistic treasures of this ancient city for centuries. Through subsidence of the island as well as sea level rise, Venice is subjected to flooding on a regular basis. The lowest levels in many of the canal-side buildings have been abandoned as undefendable.
As with St Petersburg and Amsterdam, geography conspires with climate to drive the occurrence of high water. Especially during the winter months, winds blowing from the south along the Adriatic Sea drive sea water to its restricted northern end – directly towards Venice. The shape and hydrography of the Venice lagoon further concentrates the flow, leading to repeated Acqua Alta events. Historical records of Venice in flood date back to 589. The 22 highest recorded event in modern times have occurred since 1966. Through a combination of sea level rise and land subsidence, one report projects that 76% of people living in Venice will be displaced by 2100. Another projects a 2 meter rise in sea level will submerge 86% of the city.
Unlike St Petersburg, there is not just one entrance to the body of water surrounding Venice, but several openings spread over miles of sea frontage. Starting in 1984, a project with the Acronym MOSE was envisioned that would close off the Venice lagoon through a series of inflatable barriers located at major inlets to that waterway. Construction began in 2003, and the history of the project has not been uncomplicated. The project deadline was moved from 2011 to 2018, and then to 2021. A first partial deployment was reported in October of 2020, successfully protecting the city from a surge of 135 centimeters (53 inches).
The barrier is made of 78 inflatable segments 40 meters wide, 60 meters long and 10 meters high that are filled with water and rest on the sea floor when not in use. When a high tide is forecast, the “fins” are pumped full of air and float up to project above the surface. They can be raised in 32 minutes and are designed to resist tidal surges up to 3 meters above sea level.
Costs for the system are high. Construction ran to around $8 billion and, with as many as 100 people involved in managing a deployment, each event can run to $328,000.
Summary
So four historical, cultural and economic treasures have been at least partially protected from the vagaries of geography and weather by the investment of billions of dollars in infrastructure. The investments seem to be paying off so far, and those planning and operating the systems are well aware of the additional threat of rising sea levels.
Can these examples serve as templates for other coastal cities? A recent Smithsonian article describes how several cities world-wide are looking to these examples, and especially to the integrated approach of the Dutch, to prepare for sea level rise. Locations mentioned included Norfolk, Virginia, Houston, Miami, New York, Charleston, Jakarta, Bangkok, Dhaka, Shanghai, and of course New Orleans. I vividly remember a Dutch hydrologist in a television interview following the catastrophic damage to New Orleans resulting from hurricane Katrina saying, with tears in his eyes, that we could have prevented this.
As the oceans continue to rise, engineering and construction of the kinds of barriers built for these four cities could well be a growth industry in our climate change future. How badly they will be needed, and how quickly, will depend on what we choose to do about greenhouse gas emissions. It is clear that these solutions are expensive.
Whether we decide to protect from and adapt to rising seas, or choose to wait for the disasters and then respond, may represent some of the most important decisions to be made by coastal communities all around the world. The cost of the kinds of engineering solutions presented here can be calculated (the Dutch spend about $1.5 billion per year managing their current system). The investments needed to reduce greenhouse gas emissions can also be calculated. The costs of repairing disasters will be highly variable, unevenly distributed, and hard to anticipate, as will be the degree of human suffering involved.
Sources:
Earlier essays in this series have addressed how reductions in greenhouse gas emissions could slow warming and the role an all-electric economy driven by solar energy might play in that strategy. The causes for the current rate of sea level rise have been presented along with a geological time-frame perspective on where we may be headed, and how the Gulf Stream and related global ocean currents might shift in a changing climate system.
The Summary for Policy Makers out of the Science report from the IPCC Sixth Assessment contains the predictions of sea level rise reported here and can be found at: https://www.ipcc.ch/report/ar6/wg1/
The article on the number of people living in areas to be flooded was authored by Scott Kulp and Benjamin Strauss, and is here: https://www.nature.com/articles/s41467-019-12808-z
St. Petersburg
Background Wikipedia articles include:
https://en.wikipedia.org/wiki/Saint_Petersburg_Dam
https://en.wikipedia.org/wiki/Saint_Petersburg#History
The image of St Petersburg is from NASA and can be found here:
https://earthobservatory.nasa.gov/images/148293/saint-petersburg-keeps-the-sea-at-bay
Additional information can be found here:
https://www.water-technology.net/projects/stpetersburgwater/
Amsterdam and Rotterdam
A number of Wikipedia pages provide background information on the history of flooding, flood control and the engineering works developed over time:
https://en.wikipedia.org/wiki/Netherlands#Floods
https://en.wikipedia.org/wiki/Polder#Netherlands
https://en.wikipedia.org/wiki/Zuiderzee_Works
https://en.wikipedia.org/wiki/Flood_control_in_the_Netherlands#Zuiderzee_Works
https://en.wikipedia.org/wiki/Maeslantkering
The image of Amsterdam and the Zuiderzee Works is from:
https://earthobservatory.nasa.gov/images/148799/zuiderzee-works
The image of the tidal gate as part of the Delta Works is here:
https://commons.wikimedia.org/wiki/File:Maeslantkering.jpg
Data on the capacity of the system of pumps in the Zuiderzee Works is from:
Total annual expenditures by the Dutch for coastal defenses and water management is from:
https://www.nola.com/news/environment/article_a8c86a5c-3e65-5e0e-a7ad-7cc048263515.html
Other news reports on the Dutch situation relative to climate change and sea level rise include:
https://www.nytimes.com/interactive/2017/06/15/world/europe/climate-change-rotterdam.html
https://www.rijkswaterstaat.nl/en/about-us/gems-of-rijkswaterstaat/maeslant-barrier
Venice
A Wikipedia article segment on geography, flooding and opinions on the viability of the flood barrier is here:
https://en.wikipedia.org/wiki/Venice#Geography
and an article on the MOSE system is here:
https://en.wikipedia.org/wiki/MOSE
Some early successes of the completed barrier system are reported by Rasha Aridi in Smithsonian magazine:
and by Manuel Silvestri through Reuters:
The image of the Venice Lagoon system is from Google Maps
Satellite views of the Venice lagoon with the barrier open and closed can be found here:
https://earthobservatory.nasa.gov/images/149151/venice-holds-back-the-adriatic-sea
Other sources on the Venice system include:
https://eos.org/articles/for-venices-floodgates-to-work-better-forecasts-are-needed
https://www.cnn.com/travel/article/mose-venice-flood-barriers/index.html
https://www.cbsnews.com/news/venice-flooded-as-new-8-billion-dam-system-fails-to-activate/
Summary
The Smithsonian article on the adoption of Dutch methods for flood control by other cities was authored by Jim Morrison and can be found here:
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