Working with Water
Coastal cities respond to the threat of rising sea levels with diverse design strategies at multiple scales.
March 2011
As the warmest decade on record drew to a close, representatives from the more than 190 countries attending the United Nations Climate Conference held late last year in Cancun, Mexico, made just halting progress in addressing the root causes of climate change. The conference agreements, although a step forward, set only modest limits on greenhouse-gas emissions. But as the symptoms of a warmer world become more apparent, the design community has begun to consider the consequences of climate change. Looming large among these symptoms is sea-level rise, a dynamic that has the potential to radically change the character of coastal areas throughout the world.
If the weight of the science doesn't hit home, then consider that 55 percent of private real-estate insurers are now limiting new policies in mid-Atlantic coastal areas, says Wetlands Watch, a Virginia-based conservation organization. One top-10 company will no longer insure properties within one mile of the coast. Also consider that more than 30 U.S. military installations are already facing elevated risk from rising sea levels, according to the Pentagon's most recent Quadrennial Defense Review, issued in February 2010.
The fluctuating seas
The earth has been warming for thousands of years. This very gradual warming trend took a steep turn upward around the start of the industrial revolution — a phenomenon that many researchers link to escalating carbon dioxide levels. Scientists are finding that the rate of sea-level rise is increasing as well. NASA satellite measurements show that the last decade's rate of increase is almost double that of the last century. Seas are currently rising about 1⁄8 inch per year.
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| For an especially flood-prone part of New Orleans, Waggonner & Ball has proposed transforming the streetscape into a parklike environment that would incorporate water as an amenity. Image: Courtesy Waggonner & Ball |
Experts believe that much of the rise during the 20th century can be attributed to thermal expansion. Acting as the earth's heat sink, the oceans expand like the mercury in a thermometer. But the engine behind the future threat is melting land-based ice. Tremendous deposits of ice, nine-tenths of the earth's freshwater, lie stored atop Greenland and Antarctica. The last time there was a major rise, 120,000 years ago, the sea level rose around 18 feet above current levels. But most climate scientists expect the rise this century to be in the range of 3 to 7 feet. The immediate concern is that higher sea levels will allow storm surges to inundate coastal areas more frequently, according to several recent scientific and engineering studies.
Learning from New Orleans
No single weather event can be tied directly to climate change. But the Gulf Coast is a sobering reminder of what can go wrong in a catastrophic storm. Since the devastation of Katrina, New Orleans–based architects Waggonner & Ball have been grounded in projects that respond to the issues of water management. But instead of solely considering holding the water back, the firm advocates a diverse approach that adds to the experience of the city. "The challenge is to find the balance between safety and beauty," says president David Waggonner. "And safety is not just levees. Any reasonable risk-reduction strategy deals with internal water and where it goes."
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| Waggonner & Ball's water-management scheme for one section of New Orleans includes reviving the long-ago filled and abandoned Carondelet Canal, which once connected a turning basin near the French Quarter and the Bayou St. John. The plan also incorporates a host of strategies intended to relieve the city's overburdened drainage network. Image: Courtesy Waggonner & Ball |
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| Waggonner & Ball's proposal for reviving the Carondelet Canal and reinvigorating the Lafitte Greenway depends on techniques that treat water as a resource and help absorb, slow, and direct its flow. Images: Courtesy Waggonner & Ball |
The firm has worked on several planning projects, including a proposal to reestablish a water identity for the Lafitte Greenway, where the historic Carondelet Canal once connected a turning basin at the French Quarter to the Bayou St. John and Lake Ponchartrain beyond. The plan is one option New Orleans officials are considering. The scheme incorporates diverse strategies at different scales to absorb, slow, and direct water, such as wide parklike areas along the canal that act as water shock absorbers and bioswales — landscape elements that can remove silt and pollution from surface runoff. The intent is to keep water out of the city's overtaxed underground storm system by allowing it to evapotranspire through plantings, infiltrate the soil to replenish groundwater, or gradually flow into the canal. The plan could lessen the reliance on the mammoth pumps that not only remove storm water but also lower the natural water table of the area. This decrease in the water table is a major contributor to land subsidence — New Orleans, like Venice, is sinking.
Waggonner says that in a city that has traditionally tried to keep water out, it's hard to convince people there are times when it's better to let it in. But he adds that the Dutch have inspired many of his strategies, and they have shown that it's possible to live on land below sea level.
With centuries of experience in coastal engineering, the Netherlands provides a well-tested model of water management. The nation operates the busiest port in Europe and generates 70 percent of its gross domestic product on land that lies below sea level. In 2001 and again in 2007, the Dutch government appointed a panel of scientists and engineers called the Delta Committee to make recommendations to respond to increased risks. The committee laid out an ambitious set of projects — literally shoring up coastal areas by extending shorelines outward up to several kilometers. They also proposed adding more mechanical controls like the colossal waterway surge gates at Maeslantkering, which close during threats of surges and extremely high tides.
The Dutch are also implementing a somewhat controversial plan to breach a few inland dikes and allow water back into some of the polders — land reclaimed from the sea and protected by dikes. Climate scientists believe that some higher latitudes in northern Europe may experience increased rainfall and flooding. Hence, the Netherlands could be under increased threat from land-based flooding from rivers like the Rhine that drain a substantial part of Northern Europe. Allowing water back into some polders could provide a kind of relief valve that takes pressure off lower-lying areas.
The Dutch firm Waterstudio is spearheading one experimental project in flooding polders in Naaldwijk called New Water, which includes half land-anchored and half floating buildings. One piece of the development, a floating complex of 60 residential units known as the Citadel, is slated for completion in 2012. Waterstudio has made a specialty of buoyant architecture, having completed a flotilla of "watervillas" as well as a large floating prison docked near Amsterdam. Waterstudio principal Koen Olthuis sees his work as part of a trend for cities to move onto the water instead of away from it and envisions floating platforms, 600 feet square, acting as armatures for the urban fabric.
Understanding risk
The population of coastal cities continues to grow. Now at 3 billion, the number of people worldwide living near the coasts is expected to nearly double by 2025. Many metropolitan areas are just beginning to consider the risks of sea-level rise. Miami is one of the most vulnerable cities in the U.S. with most of its neighborhoods and some $400 billion in assets lying around 3 feet above sea level. A storm surge from a Category 3 storm could submerge much of the city in 6 to 9 feet of water, according to the National Oceanic and Atmospheric Administration. Sea levels predicted for the end of the century would drive the coastline back dramatically, potentially flooding much of the city.San Francisco is perhaps more fortunate than many coastal urban areas since its bay is relatively sheltered and the region has higher areas of retreat. But it also has many assets close to or below sea level. The Bay Conservation and Development Commission sponsored a competition called Rising Tides to consider ways to adapt to higher sea levels. One of six winning entries, the Skidmore, Owings & Merrill (SOM) BayArc scheme proposed an inflatable barrier placed at the bay's entry under the Golden Gate Bridge.
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| ABOVE AND BELOW: Skidmore, Owings & Merrill has proposed a barrier to protect San Francisco Bay from periodic high water levels associated with sea-level rise. The device, which the firm calls BayArc, consists of a submerged, cable-reinforced membrane and an inflatable bladder. When deployed, the BayArc floats to the surface and creates a barrier stretching from the water's surface to the sea floor. 1 Tidal Energy Capture and Structural Anchorage 2 Buoyant Top Member 3 Sea Floor Attachments 4 Cable-Reinforced Membrane Images: © Skidmore, Owings & Merrill, 2009. All Rights Reserved. U.S. Patent Pending |
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"Our research showed that the problem would be in storm surges that occur at high tide," says Craig Hartman, design partner in SOM's San Francisco office. Add that swell to the projected sea-level rise, and many areas like the transportation corridor around San Francisco's airport could be threatened, he says.
The barrier "shaves off the tidal peak" during extreme events, says Hartman. The device has a 4-foot-high rigid band that acts like a dam at the water's surface. Below the surface, where the pressures are less, a web of tension cables hold a submerged curtain and the inflated barrier in place. Hartman relates that the deployable barrier doesn't address the long-term issue of substantial sea-level rise, but it could buy the area time to consider more comprehensive solutions.
Every coastal urban area has its own set of issues. The simple elegance of SOM's solution would have little application in New Orleans with the Mississippi River running through its heart, Lake Ponchartrain at its back, and the Gulf at its flank. But if the floodwaters of Katrina foreshadow things to come, then designers in coastal cities would do well to look at the proposals for the Gulf and the formidable challenges the region faces. On the Waggonner & Ball website there's a menu item that is fairly unusual in the profession: Research. The firm has extended its mission to engage universities, governmental agencies, and foreign countries in considering the task of saving one of America's most distinctive and culturally rich cities. Congress has ordered the Corps of Engineers to build New Orleans's levees to a 1:100 probability of flooding. Meanwhile the Dutch are building critical defenses to a 1:10,000 level. In his forward to the 2008 Delta Committee Report, chairman C.P. Veerman remarks that the document's proposals are unusual because they present an integrated plan to protect the Netherlands for centuries to come. "After all," he concludes, "a living land builds for the future."
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Soft infrastructure
New York City, with enormous assets perched on the water's edge, was one of the first cities to establish an advisory panel to look at adapting to climate change. And, recently, a group of architects, engineers, and researchers participated in an interactive brainstorming session called Rising Currents that culminated in an exhibit at the Museum of Modern Art (MoMA). The interdisciplinary teams developed a toolbox of solutions for New York's waterfront."Often the work of [governmental] agencies doesn't involve designers," says Guy Nordenson, a New York City–based structural engineer who was a consultant to MoMA and the project director on the Latrobe Prize research project that inspired the exhibit. "The point of Rising Currents is that designers can make a contribution by visualizing and representing what can be done [about sea-level rise]." The results were focused on "soft infrastructure" — elements that cushion and absorb storm surges by enhancing or emulating natural systems. The concept includes water breaks such as artificial islands or shoals and reintroducing once-plentiful oyster beds. The teams proposed softer, more parklike edges that would serve to dissipate storm surges while making the water more accessible to people.
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"If you build a wall around the inhabited areas, it's not going to help the overall ecology of the area — you've submerged wetlands that are necessary to the health of the estuary," Nordenson says. "We felt there's more benefit in designing a city that lets water in from time to time," adds architect Adam Yarinsky, a principal at New York City–based ARO and a coauthor of the book On the Water: Palisades Bay (2009), which documents the Latrobe Prize research.
Designing for resilience
In the last decade, the term resilience has come to embody a multifaceted approach to promote the ability of the natural and built environment to sustain itself through extreme events. Timothy Beatley, professor of sustainable communities at the University of Virginia, points out that most current planning models consider only 20- to 30-year cycles and are rarely coordinated at the regional or national levels. Cities like New Orleans and New York need 100- or even 200-year plans that have a broader scope and take into account ecosystems and their flood-resistant qualities, he says. Beatley also cautions that certain regions will need to consider shifting land-use patterns. "We're going to have to think about strategic retreat in some areas."For resilience at the building scale, Beatley points to the idea of "passive survivability": the ability of buildings to maintain livable conditions after the loss of essential services. Any strategy that enhances the self-sufficiency of a building can extend its viability as shelter in the aftermath of debilitating storms. Off-grid energy systems such as photovoltaics, solar water heating, and on-site water collection can keep basic services going. Reducing demand by designing in a high-efficiency envelope and using passive heating and cooling techniques can also help.
The flood-resistant building
Of course, passive survivability assumes that the structure remains intact after an event like a tropical storm or tsunami. The National Institute of Building Sciences publishes a Whole Building Design Guide on flood-resistant buildings. The guide describes strategies to allow a building to survive waterborne disasters with minimal damage.The Federal Emergency Management Agency (FEMA) publishes maps that designate Special Flood Hazard Areas delineated by a Base Flood Elevation (BFE). This benchmark is often set at the level of a 100-year flood — a flood that has a 1 percent chance of being equaled or exceeded in a given year. Local codes typically designate a Design Flood Elevation (DFE) based on the FEMA maps. Coastal zones are often more restricted since they are potentially subject to more severe conditions, such as wave action. The recent images of houses floating down the swollen rivers of Brisbane, Australia, are a reminder that the safest option is keeping new structures away from vulnerable zones.
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| Waggonner & Ball's house for the Lower Ninth Ward in New Orleans plays on the local vernacular and has a raised first floor. Image: Courtesy Waggonner & Ball |
If there's no choice but to build in a flood-prone area, a level of safety can be achieved by lifting the structure's habitable parts above the DFE. In many cases, this requires elements such as piers that can withstand hydrostatic and debris loads. Brad Pitt's Make It Right Foundation commissioned Waggonner & Ball to design such a flood-resistant house for New Orleans. The prototype plays on the vernacular of the shotgun house but raises the first floor 8 feet to protect it from flooding and provide a place to park cars.
In inland zones where the structure won't be subject to wave action, the area of the building below the DFE can
often be constructed to withstand flooding with only cosmetic damage. This strategy, known as wet flood-proofing, was explored in a winning entry in the U.K.'s Norwich Union Flood Design competition. London-based Nissen Adams developed a housing model that uses materials such as masonry that can withstand water on the lower level.
The plan is organized so that nonessential functions like bedrooms are placed on the lower level, allowing occupants to relocate to the upper floor in a flood. Dry flood-proofing is a more involved strategy of essentially making the building watertight and able to withstand extreme hydrostatic pressure. In both cases, designers should consider the buoyancy of the structure and ensure that the foundation is protected from the erosive effect of floodwaters. There is also a range of mechanical flood barriers for buildings that are either deployed automatically or manually.
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