A look at weather extremes and the big-picture climate connections.

Post Sandy, Wetlands Could Help Shore Up NYC’s Defense

By Marit Larson 
Guest Blogger

In the wake of Hurricane Sandy, the discussion of how New York City’s shoreline can be protected has taken on new urgency. So-called “soft” measures, such as wetlands and oyster reefs, are seeing a burst of new attention as possible alternatives to “hard” measures such as storm surge barriers. 

Wetlands can be very effective protection, but only if there are enough of them. In the New York City region, more than 80 percent of the coastal wetlands that once formed a ring of green around Jamaica Bay and our tidal streams are filled and developed. Were those wetlands still here, and had the development remained upland of them, the destruction from Sandy would have no doubt been significantly less or not occurred at all. 

A salt marsh recently restored in Bronx with waterfowl barrier (string and stakes), undisturbed by Hurricane Sandy's destructive force.
Credit: Marit Larson

But development is here to stay, so we now have to ask about the costs and benefits that are possible starting from where we are now. How much storm surge protection could be achieved, either by restoring historic wetlands or constructing new ones? How much wetland is practical to build given costs and competition for space? 

We know that we can successfully restore and reconstruct salt marshes. We have done more of this in New York City than many residents realize. We do it either by excavating thousands of yards of landfill and waste that was placed on top of them, or by adding clean dredged sand onto former wetlands to achieve a sustainable elevation.

These restored and reconstructed marshes have proven to be resilient to storms. Where wetlands lie adjacent to low-lying property, their rough surfaces dissipate wave energy and capture debris that would otherwise end up on streets or battering buildings. How much protection wetlands can provide altogether to an urban area will depend on how much wetland we can restore or construct.

Inter-governmental city, state and federal projects have been aimed at trying to expand the diminishing wetland footprint around the New York/New Jersey harbor for more than a decade through wetlands restoration projects. The goals for these projects are diverse. Wetlands also provide feeding and breeding habitat for fish and birds; water quality improvement due to filtering by the plants and soil organisms; recreational and aesthetic value; and, of course, storm surge protection. Despite all these uncontroversial goals, wetlands restoration and construction projects face many practical constraints in a heavily developed urban environment. 

Some constraints are technical. For example, we are working to restore and re-construct the oyster reefs of the New York Harbor estuary, which at one time were plentiful, but in recent decades have been near non-existent. These efforts are still new, and we are still trying to understand what factors seem to be limiting the self-sustainability and growth of the pilot test reefs in around the city. Water quality, wave energy, disease, predators and limited oyster seed in the water column all play a role.

Preliminary maximum extent of wetlands for Bronx, Brooklyn, Manhattan, and Queens.  Click image to enlarge.
Credit: New York City Wetlands Protection Strategy report/PlaNYC

Other constraints are regulatory. Though from a bird’s eye view, miles of open water seem like the perfect space to expand our storm-absorbing wetlands buffer, those shallow and deep intertidal waters currently provide habitat and ecological benefits that are protected and regulated by law.

Some changes in policy of the coastal environment over the next decade are likely. But those policy changes should be based on knowing the ecological impacts, benefits, and feasibility of constructing wetlands where they have not historically existed. Small on-going pilot projects in New York City and elsewhere will help us better understand the technical (and current regulatory) feasibility of these projects – the next question will be whether these approaches can be scaled up to have the buffer impact we desire. 

Alongside the question of how we can use restore and reconstruct wetlands to help protect our shorelines in the future, is perhaps the more urgent question of how we are protecting those wetlands we do still have.

Even as we note the overlap between areas of extensive hurricane destruction and tidal wetlands, properties are still being slated for development on low-lying land adjacent to tidal wetlands. Now is the time to consider reserving these lands, where possible, to allow marsh to migrate into them as the sea level rises, and to reserve their functions and benefits. There are relatively few opportunities for this to happen in New York City, in particular, but perhaps that is all the more reason for us take advantage of them.

Marit Larson is Director of Wetlands Restoration for the City of New York Department of Parks & Recreation's Natural Resources Group (NRG), where she has reviewed, designed and constructed freshwater and tidal wetlands for more than 10 years. Her group is studying salt marsh vulnerability and restoration opportunities under different sea level rise scenarios with a grant from U.S. EPA. As a consulting hydrologist, she has worked on urban stream and wetland restoration and projects in the Eastern U.S., the Pacific Northwest, Germany and Australia. She lives in New York with her husband and two sons.

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By bydlo
on November 12th, 2012

Any soft measures aimed at preventing or migitating storm surge damage at this point are doomed to be insufficient. With a sea level rise of 3 to 6 feet forecasted for this century, the wetlands and oyster beds will have no place to retreat unless thousands of people and many businesses are uprooted.

The only viable solution for New York to migitate or prevent storm surge damage and eventually sea level rise damage is to build a vast network of ocean barriers, like those protecting Venice, London or Rotterdam. These barriers have an excellent record of protecting everything behind their mighty gates and they are the only solution to the storm problem that I know would be comfortable having my tax money spent on.

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By Thomas Freed (92612)
on November 23rd, 2012

During the <a >property restoration Reynoldsburg</a> and now for this people, that is to say, previous homeowners have probably also taken matters into their own hands, making decor changes to the appearance of the structure. For some, it may have been a simple painting of the bricks to be more appealing to the times. Others may have made changes with other applications like stucco covering over the brickwork.

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By Peter Sheng (Gainesville, Florida 32607)
on October 6th, 2013

“These policy changes should be based on knowing the ecological impacts, benefits, and feasibility of constructing wetlands where they have not historically existed. Small on-going pilot projects in New York City and elsewhere will help us better understand the technical (and current regulatory) feasibility of these projects – the next question will be whether these approaches can be scaled up to have the buffer impact we desire.”

I agree with these statements. Before implementing any plan to restore wetlands where they either historically existed or not, it is necessary to quantitatively estimate the benefit and cost of these plans.

Here is a paper which describes a model that can be used to assess the effectiveness of wetlands for mitigating storm surge and coastal inundation:

The Reduction of Storm Surge by vegetation Canopies - Three-Dimensional Simulations.
Sheng et al., 2012, Geophysical Research Letters, Vol 39, L20602, doi:10.1029/2012GL053577.2012.

If you cannot find it and needs a copy, please email me at pete@coastal.ufl.edu.

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