Editorial: 鈥�Don鈥檛 let the Big Apple rot鈥�
Read more: 鈥�Protecting New York City from the next big storm鈥�
Lower Manhattan smells damp. Down near the Staten Island Ferry building, all the lights are still out. Utilities trucks line the streets and thrum like sleeping dragons, pumping seawater out of the subway tunnels.
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It is four days since superstorm Sandy ripped through the north-east US, killing more than 110 people and leaving much of this part of New York City underwater. Most of the streets are clear now, but a tunnel on West Avenue is still impressively flooded, drawing locals on bikes to snap photos.
On a cross street, cars splash water onto gritty sidewalks strewn with detritus. Workers are wearing head-to-toe plastic suits. My guide, of New York鈥檚 Regional Plan Association, tells me that the water being pumped onto the street is full of subway garbage.
The city has a lot of immediate damage to worry about, but this isn鈥檛 a problem that will go away, even once the streets have dried out. Sea-level rise and increasingly frequent storms mean the city鈥檚 underground infrastructure is corroding 鈥� and it is only going to get worse.
鈥淣ew York is degrading from underneath,鈥� says , a civil and environmental engineer at the Polytechnic Institute of New York University. 鈥淲e are facing a situation where a decade from now, we will start seeing failures of infrastructure.鈥�
The problem is salt plus time. Much of the city鈥檚 vital infrastructure 鈥� utility pipes that carry gas, water and electricity, plus the extensive subway network 鈥� is made of steel and buried deep underground. Buildings and bridges are built on foundations made of steel-reinforced concrete. Under normal conditions, dirt and concrete shield the steel from the corrosive effects of water and oxygen. The steel can also grow a protective layer of dense, crystalline rust that actually protects it from further disintegration.
But when salty water gets in, whether by seeping through over time 鈥� from the groundwater, for instance, or surrounding water in the case of bridge piles 鈥� or because the concrete foundations have been worn down by acid rain, that protection disappears. The ions in salty water can generate an electrical current between one part of a metal bar and another, similar to the current in a chemical battery, and this process eats away at the metal until it is consumed and replaced by rust. The saltier the water is, the faster it happens.
For steel-reinforced concrete, sudden floods like Sandy鈥檚 will probably not make too much of a difference. But rising sea levels, driven by global warming, will.
We still don鈥檛 know exactly how much sea level will rise this century. It鈥檚 unlikely to be more than 2 metres by 2100, because glaciers and ice sheets 鈥� whose slow slide into the ocean climate change is accelerating 鈥� can only move so fast. Most climatologists expect it will be about 1 metre.
To make matters worse, climatologists suspect that New York state is going to get more than its fair share of sea-level rise. Tide gauges show that the rise on the eastern seaboard is accelerating four times faster than the global average. This is consistent with model predictions for the rest of the century ().
鈥淭here is clearly a potential for a greater than average sea-level rise on the eastern seaboard,鈥� says at the University of Copenhagen in Denmark. If the global average rises 1 metre by 2100, New York could well see 1.15 metres, he says.
Rising seas have insidious effects. Earlier this year, Yale University asked one of their geologists, , to look into the consequences for the area around their campus in New Haven, Connecticut, 100 kilometres up the coast from Manhattan. The university wants to expand the campus and was making sure its plans were well informed.
In a , Skinner found that a sea-level rise of nearly 1 metre would cause groundwater within 2 kilometres of the coast to rise by the same amount. Rainfall is also expected to increase in the area, making the groundwater rise further, and further boosting the risk of flooding.
Driven by rising seas, the swelling groundwater will become saltier. This will not be a problem for drinking water in New Haven, which doesn鈥檛 draw groundwater for human consumption any more, says Skinner. But metal infrastructure such as water pipes and girders built into foundations will all corrode.
Similar problems鈥�� flooding and corroded foundations鈥�� can be expected in cities across the eastern seaboard, where, in some cases, the existing infrastructure is already nearly a century old.
Nor are rising sea levels and the resulting flood risk the only risks climate change poses to urban infrastructure. Storm surges like the one brought about by Sandy are made more likely by rising sea levels, and can make corrosion worse. 鈥淚f you have cycles of wet-dry-wet-dry, that is sometimes even more damaging,鈥� Ghandehari says, because the dry cycles let in oxygen, which accelerates corrosion.
鈥淲ith the combination of ageing and climate change, we have a situation where you really can鈥檛 take anything for granted,鈥� says Ghandehari.
No denying it
It is difficult to know how bad things already are. Because the utility pipes are out of sight underground, it鈥檚 costly and inconvenient to check them for damage. Ghandehari compares the city鈥檚 network of pipes to a human body: the health of both degrades as they age, and getting a medical every so often is critical. But we have fewer diagnostic tools and no health insurance for underground infrastructure.
鈥淭he ultimate risk is that we do not see what鈥檚 happening, so we cannot take action at the right place at the right time,鈥� Ghandehari says. 鈥淚t鈥檚 like not getting a check-up, and then all of a sudden having a heart attack.鈥�
Engineers are already developing new diagnostic tools. Small robots can explore gas lines. Electric lines can be probed with an electromagnetic pulse, the speed and shape of which changes if it encounters any defects. And water pipes can be inspected using ultrasound.
But for new pipes, Ghandehari suggests a much lower-tech solution: put utility lines in tunnels that human workers can walk through. 鈥淭he rule of thumb is that you need to have access for inspection,鈥� he says. 鈥淐ities of the future should consider how to deal with providing access to the urban lifeline.鈥�
In the meantime, New York has some difficult decisions ahead as it recovers from Sandy. 鈥淭he hard thing is going to be where to rebuild, and where not to rebuild,鈥� Barone says.
It might be best to leave some neighbourhoods uninhabited so that they can take the brunt of future floods. 鈥淲e had built on barrier islands,鈥� Barone says. 鈥淲here an entire neighbourhood has been destroyed, do you rebuild it? Or do you do something else?鈥�
It鈥檚 a cruel calculus, but for the shoreline just north of New York City that was hit by hurricane Irene last year, Sandy鈥檚 aftermath is all too familiar.
鈥淚n two years, most parts of the region have been touched by natural disaster,鈥� Barone says. 鈥淲e can鈥檛 assume this will be every 10 or 20 or 50 years any more, like we used to. We are going to have another one.鈥�
