How cities are revamping their coastal defences

A soft breeze ruffles the grass taking root on Rockaway Beach, the tufts forming a loose grid that captures blowing sand and helps restore the dunes along this low-lying peninsula on the southern edge of Queens in New York City.

Delicate as the slender stalks are, they forge critical armour for the 3.5m cubic yards of sand that is being spread on the beach by the US Army Corps of Engineers. The project will help return this stretch to its pre-1970s elevation of 10ft or more above sea level.

On a sunny Saturday in August, the shore is crowded with New Yorkers who have traded city streets for beach blankets and a dip in the Atlantic. Yet for the second summer in a row, sunbathers and surfers must share space with heavy construction equipment as workers replenish the sand, reconstruct the boardwalk and reinforce the shoreline against rising sea levels and severe weather, helping to protect the roughly 100,000 people who live on this narrow strip of land.

It has been nearly two years since Hurricane Sandy caused a 14ft storm surge to hit New York, which washed away houses, left millions of people without power, ripped boardwalks from beaches and flooded transit tunnels, causing damage that cost the city an estimated $19bn. The storm inundated 46.2 sq miles of the city – an area 65 per cent larger than what had been deemed at risk on the federal flood maps in use at the time, according to the National Resources Defense Council.

While life has returned to normal for many New Yorkers, the flurry of activity in hard-hit neighbourhoods like the Rockaways is just the beginning of a long-term plan to rebuild damaged areas, strengthen protections against future flooding and storms and reduce the city’s contribution to global warming.

“It’s been great progress but it’s early. Ten months into a 10-year plan, we’ve made some significant headway,” says Daniel Zarrilli, who heads New York mayor Bill de Blasio’s new office of recovery and resiliency.

An engineer who rode out the 2012 storm at his home on Staten Island, Zarrilli was asked by de Blasio’s predecessor, Michael Bloomberg, to produce a plan to rebuild the city after Sandy. He is now overseeing the implementation of many of those proposals, including restoring 26,000 linear feet of dunes on Staten Island, updating building codes, moving electrical systems to higher floors and repairing subway tunnels corroded by saltwater.

The city plans to spend $3.7bn on coastal protection; Zarrilli says more than half that amount has been funded. Studies show that every $1 spent on mitigation – efforts to reduce risk before disasters occur – saves $4 in recovery costs.

The question of how best to protect New York’s 520 miles of coastline and 8.4m residents, almost 3m of whom live in designated hurricane evacuation zones, has generated a huge number of ideas from engineers, ecologists, urbanists and architects.

Among the proposals are oyster beds that would help absorb storm surges and retractable flood walls that would unfurl to protect lower Manhattan from rising water. Solar and wind-powered batteries and “smart microgrids” would keep electricity flowing even when a storm knocks out traditional power lines.

Barriers at the mouths of Brooklyn’s Gowanus Canal and Newtown Creek on the Brooklyn-Queens border would help keep dry the growing number of residents and businesses housed in the city’s floodplain.

Many of these projects have already won federal grant competitions, such as the US Department of Housing and Urban Development’s Rebuild by Design contest, which allocated $920m in disaster relief funds to six proposals in New York and New Jersey.

The biggest grant, $335m, went to the Big U project, which would wrap lower Manhattan in a series of parks and walkways incorporating berms and barriers under the FDR Drive, an elevated roadway, that can flip into position in event of a flood and protect buildings and electrical substations from water.

A design to slow waves and buffer erosion with a necklace of artificial reefs off the south shore of Staten Island won $60m. During Sandy, storm surge and high waves battered the island’s shores, resulting in the destruction of buildings at a higher rate than in the city as a whole. The breakwaters would also be a boon to local ecology by serving as habitats for fish, shellfish and lobsters.

A $20m proposal for Hunts Point in the Bronx would include a greenway and flood protection structures along the waterfront of a neighbourhood that plays a key role in the city’s food supply network. Fresh food from around the world arrives at wholesale markets in Hunts Point where it is sold on to restaurants, supermarkets, schools, food banks and soup kitchens. While the peninsula, framed by the East River and Bronx River, emerged relatively unscathed from Sandy, its low elevation has raised concerns over its vulnerability to rising sea levels and the impact that any disruption to food distribution would have on millions of people across the region.

The decision by city and federal officials to focus on these kinds of targeted, location-specific projects is part of a “comprehensive strategy that looks at a broad range of climate risks,” says Zarrilli.

Studies show that every $1 spent on mitigation – efforts to reduce risk before disasters occur – saves $4 in recovery costs

In the immediate aftermath of Sandy, there were proposals to build a huge flood barrier across the mouth of New York harbour. Yet the costs associated with such a plan – $15bn to $22bn by some estimates – would likely be prohibitive.

Similarly, fully hardening the shoreline is dismissed as unrealistic. “This is a living waterfront. There’s fish, birds, people that use it and need access. Building a 12ft-high seawall all around the city is clearly not the right solution,” says Rob Pirani of the non-profit Hudson River Foundation. Such large-scale solutions also do not address the underlying factors behind rising sea levels, which experts say present the biggest challenge for low-lying cities around the world such as New York, Miami, Guangzhou and Mumbai.

“It’s the silver-bullet solution that doesn’t address the risks we face. Locally tailored solutions to specific risks in each community is a much more cost-effective way of reducing the long-term risk,” says Zarrilli.

Sea levels in the New York region have risen about one foot over the past century, according to data collected at tide gauges on the Battery at the southern tip of Manhattan. By the year 2100, the sea could rise another six feet as the polar ice melts, according to projections from the New York City Panel on Climate Change.

That would make flooding from another storm like Sandy much worse – and the panel predicts severe storms will become more frequent and bring higher surges. “Whatever storm comes along, there will be increased coastal flooding due to sea level rise. So the risks of coastal flooding are increasing right here due to climate change,” says Cynthia Rosenzweig, a climate scientist at the Nasa Goddard Institute for Space Studies who co-chairs the panel.

The city is grappling with the risk of rising sea levels after a pledge first made in 2007 by then-mayor Bloomberg for a 30 per cent cut in greenhouse gas emissions by 2030. Zarrilli says New York is ahead of schedule, with emissions down 19 per cent since 2005.

There is also a human element to New York’s recovery and future disaster preparations. Pirani, of the Hudson River Foundation, emphasises that “resilience is more than physical infrastructure – it’s also the social networks that we saw played a huge role in coping with the aftermath of Sandy”.

New York’s current mayor echoed the sentiment during a visit in August to Red Hook, a working-class stretch of Brooklyn’s southwestern waterfront where homes and shops were flooded and residents of a huge public housing project were left without power for weeks after the 2012 storm.

“God forbid we see anything like Sandy again, but we have to be ready in any event. We want to make it better for people. We want to get them more ready for anything thrown at them,” de Blasio said during the visit. “It is a reminder of a new reality we’re living with, the reality of climate change. The events that we used to consider extreme weather are becoming more common. We can’t act like they’re unexpected.”

Shannon Bond is the FT’s US media and marketing correspondent

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Cities under threat

With more than half the world’s population living in cities and global wealth accumulating, flood damage costs are set to rocket as warmer temperatures raise sea levels.

London The Thames Barrier, completed in 1982, spans 520 metres downstream of the UK capital, making it one of the world’s largest moveable flood barriers. Closing all 10 gates takes about 90 minutes and protects 48 sq miles of London. As of March this year, the barrier had been closed 174 times since it opened – half of the closures were to protect against tidal surges from the North Sea and half to alleviate upstream river flooding. It is hoped the barrier will continue to be effective until the end of the century.

Guangzhou China’s third-largest city faces the highest financial impact from flooding of any major coastal city, according to the OECD. About 13 per cent of the Pearl River delta is below sea level, and water levels along coastal Guangdong province have been rising faster than global averages, according to China’s State Oceanic Administration. The provincial government this year called for cities including Guangzhou to upgrade drainage and sewage lines and engineer new flood control systems that will allow them to weather flood heights associated with the worst storms.

Melbourne Sea levels along Australia’s southeast coast are projected to rise almost 2ft by 2070, threatening swaths of the country’s second most populous city. Melbourne’s 1200 Buildings programme aims to retrofit more than two-thirds of the city’s commercial structures over the next decade. The plan calls for buildings to cut emissions, water use and energy consumption as part of the city’s goal to reach net-zero carbon emissions by 2020.

Ho Chi Minh City Perched on the Saigon River, Vietnam’s largest city is expanding toward the sea as its population grows beyond the current 8m. But the river that is the city’s economic heart is also the source of increasingly frequent flooding, and current urban development plans will leave two-thirds of Ho Chi Minh City at flood risk by 2025. The city has struck a partnership with Rotterdam in the Netherlands to adopt best practices from its Dutch counterpart, including increasing water drainage and storage capacity and building more resilient waterfront infrastructure.

Photographs: Robert Stolarik; Reuters; Rebuild by Design