Yesterday New York City Mayor Michael Bloomberg revealed a $19.5 billion plan to protect his home town against future sea level rise and other effects of climate change such as heat waves. The big focus, however, is preventing death and damage from another Hurricane Sandy. The report, “A Stronger, More Resilient New York,” prescribes 250 projects ranging from big stone walls to little flood gates intended to hold back storm surges and fend off rising seas. Some of the steps agree with recommendations made by scientists in a feature article I wrote in the current (June) issue of Scientific American, and some steps contradict what those scientists said. But in total, the plan really calls for surrounding New York City with high levees, sand dunes and wetlands—much like the “natural” defenses that the U.S. Army Corps of Engineers has been building around New Orleans.

That’s because the Corps has strongly influenced the New York plan.

The city’s Special Initiative for Rebuilding and Resiliency prepared the 430-page document as an addition to a larger, ongoing “plaNYC” blueprint for making the city sustainable for many decades. The scientific basis for the protection plan is sound. It forecasts a rise in sea level of 11 to 24 inches by 2050, with a potential high value of 31 inches—which is on pace to reach the five feet, plus or minus one foot, by 2100 that scientists predicted in my article. The numbers come from a report released on Monday(pdf) by experts on the New York City Panel on Climate Change, who were among my main sources as well.

In a long speech, Bloomberg stated that because of sea level rise, future storms much smaller than Hurricane Sandy could do as much damage or more—a laudable recognition of increasingly severe weather brought about by climate change, and a stand that few members of Congress are willing to make at the national level. The plan notes that by 2050 some 800,000 residents will live in the city’s flood zone—which will cover more area than it does now because of sea level rise. About 400,000 live in the zone today.

Yet Bloomberg dismissed the two biggest recommendations scientists made to Scientific American. He said erecting a large flood barrier across New York Bay to protect the entire city against storm surges “is just not practical or financially feasible.” And he said that “We cannot and will not abandon our waterfront,” meaning the city will not ask (or require) people who live in low-lying areas to move away from the water’s edge, even in places that are repeatedly flooded by minor storms. These are the two ultimate steps that scientists told me were necessary evils, even though the first is expensive and the second is politically unpopular.

Instead, the city will pursue a boatload of smaller, local projects that will attempt to protect specific shorelines and neighborhoods. These include flood walls, breakwaters, small flood gates across creeks or canals, reconstituted wetlands, long levees, dunes, double-dunes (the first dune breaks up the waves; the second, higher dune holds back flood water) and sand piled on beaches to broaden them. The New York Times posted a nice set of maps today that shows the locations of the proposed structures.

Bloomberg appears to be ready let the Corps decide how to pursue the projects, referring to the engineering group repeatedly in his speech. The plan also cites the Corps, which carries out Federal flood protection projects, numerous times. It includes a highlighted statement noting that the Corps “has been an important partner for New York City in the past. The importance of this partnership will only grow as the city seeks to implement the coastal protection projects described in this report.”

That may be because the Corps can get things done—with taxpayer money from America’s coffers. The Corps proposes projects to Congress, which then decides if it will fund them. By going though the Corps, people from Oklahoma, Montana and the other 48 states will pay for encircling New York City with sand and dirt. During his speech, Bloomberg explained that of the $19.5 billion price tag, $10 billion will come from Federal relief funds and city capital already allocated; $5 billion from additional, expected Federal relief funds; and “additional Federal funding and city capital” for the remaining $4.5 billion.

The Corps has done good work around New Orleans. And many of the steps proposed for New York make good sense. But the Corps has also been criticized, as it was after its protection scheme for New Orleans failed during Hurricane Katrina, for continuing to follow the same strategies it has followed for decades—piling sand onto beaches and dirt into levees. It is also sometimes faulted for not listening to scientists who may have other ideas, or not seeking lessons from projects outside the U.S. that are already proving their worth. Those projects include a 15-mile-long barrier outside Saint Petersburg, Russia, a system of levees and barriers in the Netherlands, and large flood structures in England, Italy and elsewhere.

Bloomberg did take the levee concept a step further, noting that levees can be topped with esplanades so residents can frolic by the sea. He also proposed an entire new complex called Seaport City on top of raised ground that would protect the lower east side of Manhattan. “Why can’t coastal protection also be a beautiful esplanade? Why can’t coast protection also be a new neighborhood?” he asked. Good for him.

Some of the proposed long levees would stand 15 to 20 feet high, and may face stiff resistance. Bloomberg refuses to ask people to retreat from the sea because the proximity is part of their neighborhood identity and economy, but a 20-foot levee will cut people off from the ocean, which seems like a similar issue.

In addition, it is unclear where all the sand will come from to build up beaches and double-dunes that will inevitably erode away and have to be replenished every five to 10 year, as the Corps now does around the country. Such projects require sand of a specific grain size, stores of which may be dwindling out in the ocean, according to experts outside the Corps.

The plan has other potential traps as well. It calls for rebuilding wetlands as a way to lessen waves and absorb some of a storm surge. Yet it pretty much acknowledges that insufficient data exists to prove that wetlands have those protective effects. Around New Orleans, the rule of thumb is that every mile of healthy wetlands can absorb one foot of storm surge. The Louisiana delta has many miles of wetlands, but there are few places around New York’s five boroughs where a mile of open water could be filled with wetlands, because the boroughs are close together and the water is full of daily boat traffic. Wetlands could improve the water’s health, which might be desirable, but it’s hard to justify them for storm protection.

Overall, Bloomberg and the Special Initiative for Rebuilding and Resiliency are to be commended for creating a thorough plan of action against sea level rise and storm surges, one that could inspire other cities to act regardless of whether nations do. They are also to be commended for requiring power plants and hospitals to harden their facilities against high water, as well as blackouts that may result from greater stress on the electric grid as temperatures rise.

The rest of the country may push back against Bloomberg’s reliance on federal funds. The mayor also wants a break from the National Flood Insurance Program. It was just revamped so that Federal subsidies will drop, requiring local homeowners and businesses that build in harm’s way to shoulder much more of the actual cost of insurance. Bloomberg said he will petition the Federal government for “partial rate reductions.”

That may sound a bit self-important, an outlook that the rest of the country sometimes accuses New York City leaders of holding. But I guess it doesn’t hurt to ask.

Photo courtesy of drpavloff on Flickr