London Thames Barrier. Source Fotolia # 30649864.

+ Even before Sandy hit New York City, there had been calls for a sea barrier similar to London’s Thames Barrier or the flood control measures in place in the Netherlands. Hurricane Sandy will certainly reinvigorate these discussions.

Despite calls for massive investment in flood barriers, I think what Hurricane Sandy really shows is that there is no single solution to urban flood resilience. Instead, we need to design redundancy and flexibility into all infrastructure to create resilience and mitigate disaster risk in cities.

Even before Sandy hit New York City, there had been calls for a sea barrier similar to London’s Thames Barrier or the flood control measures in place in the Netherlands. Hurricane Sandy will certainly reinvigorate these discussions.

A barrier protecting the New York harbour could cost as much as $29bn. In terms of arithmetic, this compares favourably with the potential cost of Hurricane Sandy – including the economic impact. But there’s more to this than arithmetic.

An infrastructure project of this magnitude would be a massive undertaking. It would involve numerous city and state agencies, pose an incredibly complex construction challenge, and require a lengthy construction programme.

What’s more, engineering systems alone are only as good as their next failure. You just need to look back at the failure of the levees in New Orleans during Hurricane Katrina to see this. We need to design in flexibility and redundancy – by creating infrastructure with spare capacity and supporting this with additional measures to cope in the event of a disaster.

To see an example of how infrastructure can work with climate change, you just have to look along New York's waterfront to Queens, where Hunter’s Point South is currently under construction. Here, storm water planters and bio-swales will soak up water draining from the streets while one third of the sidewalks will be porous concrete, increasing the infrastructure’s absorption rate.

As homes and neighbourhoods are re-built in the wake of Sandy, we must plan adaptive strategies and consider seriously whether any communities should be relocated. If the decision is to re-build, then those new communities need to be designed to be resilient.

Cedar Rapids, Iowa, underwent a similar planning exercise in 2008 when floods decimated the city. For Treasure Island, a new sustainable regeneration project in San Francisco Bay, the shoreline will be stabilized and re-graded to account for predicted sea level rises by 2050, 100-year tide elevation and bay mud settlement.

Out of Sandy comes an opportunity to plan our future. Cities at risk will need resilient infrastructure masterplanning frameworks to identify suitable solutions.

Protecting critical infrastructure such as electrical substations, transportation tunnels and wastewater treatment plants is imperative. And combating 14-foot storm surges will require a multitude of solutions, including some large-scale ‘hard’ infrastructure investments, restoration of natural ecosystem services, green infrastructure and resilient urban planning.

If there is one lesson to take away from all this: natural disasters like Hurricane Sandy will happen again but the damage to cities can be mitigated through robust strategic resilience planning. Sadly for the city of New York, this planning needed to start yesterday.