How Coastal Engineering Aims to Rescue Cities From Sea-Level Rise

by Jeff Link
- Aug 30 2016 - 5 min read
coastal engineering sea level rise header
Image animation: Brandon Au

Just off the southern shoreline of North San Francisco Bay Estuary, one can look into a possible future decades down the road, when, according to some climate-science experts, the San Francisco Bay waterline will rise more than 3 feet.

Judging from virtual-reality scenarios forecasted using OWLs—interactive devices resembling the coin-operated binoculars commonly found at national parks—that future is one of higher water, shrinking shorelines, and increasing flood risk.

The dangers of sea-level rise, of course, are not limited to the Bay Area. According to a comprehensive global research study from 2007, 634 million people—about one-tenth of the world’s population—live in low-lying coastal areas and are at risk of ocean-change impacts. Civil engineers and coastal engineering will play a major part to help low-lying cities survive.

coastal engineering Navigation Canal Lake Borgne Surge Barrier
The Inner Harbor Navigation Canal Lake Borgne Surge Barrier near New Orleans, completed in 2013. Courtesy of U.S. Army Corps of Engineers.

To put this in a human and economic perspective, a think piece called Facing Up to Rising Sea-Levels (PDF), published in 2010 by Building Futures and the Institution of Civil Engineers, reported that about 10 million people live in flood-risk areas in England and Wales. According to the report, 2.6 million properties are at direct risk of flooding from rivers or the sea, and home-insurance firms in the United Kingdom are set to lose £4 billion a year by 2035.

These predictions are leading to more speculative, multidisciplinary—and potentially more consequential—professional roles for the architecture, engineering, and construction crowd. Civil engineers are being called on to come up with new science and practices around sea walls, stormwater drainage, and groundwater tables. And they’ll also need to design safely raised roads and railways while accounting for surrounding buildings. Meanwhile, architects are designing elevated site plans based on changing FEMA maps and adhering to new building codes requiring greater wind-load resistance.

Beyond Sea Walls: New Orleans Reconstruction. Few are more versed on the subject of sea-level rise than G. Wayne Clough. The president emeritus of the Georgia Institute for Technology and former secretary of the Smithsonian chaired the committee that oversaw reconstruction plans for New Orleans after Hurricane Katrina.

He says the city represents both a cautionary tale and confounding example of the difficulties of making coastal cities more resilient: The levees blamed in part for the devastating human toll of a superstorm claiming 2,000 lives have been rebuilt with a new retention system that raises the height of the sea walls and improves their resilience with higher clay content, gravel reinforcement, and stoppage gates to control water flow.

Still, the $15 billion New Orleans reconstruction project, which took place during the past four years, is far from a perfect solution. The sea walls are designed to tolerate flood events up to a 100-year storm, which, statistically, has a 70 percent chance of occurring at least once during the next century. Plus, the sea is rising even as New Orleans, which sits on a subsidence basin, is sinking. “It will get worse with time,” Clough says. “The sea-level rise of 2 to 2.5 feet will take 100 years to develop. Hurricane Katrina, 80 years from now, will be acting on a sea level much higher and more likely to overtop levees.”

coastal engineering Gerald Desmond Bridge concrete
Concrete placement on the Gerald Desmond Bridge replacement project, using a movable scaffolding system. Courtesy Port of Long Beach.

Thankfully, there are other things being done: resiliency strategies that run the gamut from reducing carbon emissions (which mitigates sea-level rise) to creating artificial wetlands and devising city-evacuation plans—a key part of the New Orleans model.

“Everybody is looking for answers other than building sea walls,” Clough says. “If you need to build a sea wall for a 10- to 15-foot storm surge, that comes at incredible cost. Donald Trump thinks it’s cheap, but I’m sorry, it’s not. There is more and more understanding that hurricane protection is not a matter of a single structure, but a combination of strategies.”

AECOM Sea-Level Rise Simulation Maps: Port of Long Beach. Doug Sereno, director of the Program Management Division for the Port of Long Beach, understands the importance of such a varied approach. The city’s engineering and environmental divisions are currently collaborating on an AECOM climate-resilience study, which includes a working set of projected 2025, 2050, and 2075 inundation maps overlaying—in 3D—the city’s roads, bridges, railways, electrical systems, and ports. “The maps can show all these areas submerged and analyze if they are connected to an ocean, or connected to each other, and how extensive the flooding would be,” Sereno says.

The study has informed, among other projects, the replacement of the Gerald Desmond Bridge, a major access point to the Port of Long Beach, which carries I-710 over the port’s inner harbor to Terminal Island. Lead design companies Arup North America and Biggs Cardosa Associates collaborated on the six-lane, cable-stayed design, which includes a 205-foot clearance—an added six feet accounting for sea-level rise—to allow cargo ships to enter the Port. “It’s a large investment if you think about it; the six feet of height means you must accommodate a whole new grade.”

Low-Regret Decision Making. Of course, none of this predictive work is all that straightforward. AECOM’s simulation maps and software tools such as Autodesk InfraWorks 360 make it easier for civil-engineering firms to visualize adaptive changes to utilities, roadways, right-of-ways, and drainages. But without certainty as to what the future will bring—at what rate carbon will be released into the atmosphere, how fast ice caps in Antarctica and Greenland will melt, and how much the sea will actually rise—this work requires an adaptive risk-management approach based on a range of possibilities.

coastal engineering Gerald Desmond Bridge tower
Tower construction of the Gerald Desmond Bridge. Courtesy Port of Long Beach.

“One of the uncertainties is what the driving effects for climate change and sea-level rise will be,” says Richard Wright, chair of the ASCE Committee on Adaptation to a Changing Climate. “Another is the local effects: global warming is more focused in the Arctic, where average temperatures have increased much more than in the other parts of the world.”

Wright, a contributor to ASCE’s 93-page report, Adapting Infrastructure and Civil Engineering Practice to a Changing Climate, says that although such climate uncertainty presents daunting design challenges for civil engineers, there is a progressive way forward. He offers the example of the planning and redevelopment of the LOSSAN Rail Corridor running from Los Angeles to San Diego, where the height of precast concrete piers can be increased if sea-level rise is on the severe end of the spectrum.

“In the observational method for adaptive risk management, civil engineers design for the most probable intensity of a hazard over the infrastructure’s service life, such as a 100-year recurrence interval flood,” Wright says. “But if needed, engineers can make the system adaptable to a more severe, maximum credible hazard. This is what we call ‘low-regret decision making’ because it works well across all the potential scenarios.”

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