Tue, Sep 12, 2017 - Page 9 News List

How to rebuild cities after hurricanes like Harvey

The aftermath of a disaster often focuses on getting back to normal, but do cities need to think harder about how to withstand the next one?

By Oliver Milman  /  The Guardian

Studies have shown that hurricanes are likely to get stronger, if not more frequent, threatening coastal areas that are growing in population size.

This challenge, plus the pummeling experienced during storms such as Katrina and Sandy, which hit New York and New Jersey in 2012, has forced several cities to think about more natural defenses to water, rather than simply rely upon levees and pumps.

“In Houston and elsewhere we’ve encroached upon our floodplains and we aren’t leaving any natural environment to slow the floodwaters,” Knight said. “We build dams and levees and people assume they are safe behind them, or downstream from them, but look at New Orleans — the levees failed.”

Knight said her initial training as a hydrological engineer focused on getting floodwater off your land as quickly as possible.

“But we’ve learned that’s not the best way to deal with floods,” she said. “We have a completely different landscape and climate now. They are complete game changers.”

In the 1950s, Dutch policymakers headed to New Orleans to learn how the city pumped excess water out into Lake Pontchartrain.

A year after Katrina hit, the Netherlands returned the favor by briefing officials from the Louisiana metropolis about the Dutch mantra of “living with the water.”

This principle involves huge fortifications in key areas against floodwater — New Orleans now has the largest flood barrier in the world — but also emphasizes the need for “green” infrastructure such as grass, woodland and wetlands to soak up water.

Innovations such as “green” rooftops, where plants absorb some rainwater before it is funneled to barrels rather than onto the street, and permeable pavements are also being embraced.

There are seven “rain gardens” in New Orleans — essentially parks where water pools and is absorbed — and the city is spending a further US$220 million on new green areas that will draw away water that would otherwise end up in the streets or in people’s homes.

Building codes have been tightened up to focus more heavily on flooding.

New Orleans is a different sort of city to Houston — it is older and has less available land to be eyed by developers — but Hebert said its approach can be replicated.

“After Katrina, we realized we had to live with water within the city,” he said. “We have hard infrastructure such as pumps, but also nature-based solutions because pumping can’t handle it all. We had to go back to what existed in the city in the 1930s and 1940s, before mass development took place.”

The idea that water must be given space to flow in times of flood is not new; the Yolo Bypass was constructed in the 1930s to relieve Sacramento from the severe floods that plagued it.

However, many US cities are still developing close to low-lying coastal and riverine areas with barely a nod to what floodplains actually do.

Some have leaned heavily on technology — Miami Beach, which has felt the effects of Hurricane Irma, has spent hundreds of millions of US dollars on raising its streets and developing a network of pumping stations. The low-lying city sits on a barrier island that already regularly floods on sunny days due to hide tides.

“Many cities have dams, levees and flood walls which are a fairly narrow and inflexible response to flooding,” WWF global freshwater lead scientist Jeff Opperman said. “There is growing appreciation in the US that we need to diversify, to set the levees back, use natural vegetation and allow the river room, but then there’s political decisions around development and that’s a less rational process.”

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