Off-shore sea gates could protect New York

Damages caused by Hurricane Sandy.
Damages caused by Hurricane Sandy.
Bob Pool/Shutterstock
Damages caused by Hurricane Sandy.

Off-shore sea gates could protect New York

The effort faces objections, but it may be the best way to hold back storm surges.
July 1, 2020

Over the past few months we’ve experienced global pandemic, social isolation, economic collapse, political dysfunction and civil unrest. What’s next – a plague of locusts? Well, yes, in large areas of the country hordes of 17-year locusts are reappearing to eat everything in their path. An infestation of white sharks? Well, yes, they, too, are a growing problem on much of the US’s northeast coast. It’s enough to make you want to lock the bedroom door and pull the covers over your head. 

However, an even larger threat deserves our attention: the prediction by the National Hurricane Center that we can expect a greater than normal number of hurricanes in the current hurricane season.And both the National Academy of Sciences and the New York Academy of Sciences predict that the New York region will face more frequent and severe hurricanes in the years to come.

This year’s hurricane season began on June 1 and extends through the end of October. You would expect that nearly nine years after Super Storm Sandy devastated the region we would be well prepared, but this isn’t the case. After nearly a decade of bureaucratic fumbling and delays, virtually nothing has been built to prevent a recurrence of the flooding, loss of life, many tens of billions of dollars in property damage and extensive disruption to the region’s infrastructure economy wrought by Sandy. 

Earlier this year, in a short-sighted, politically motivated action, President Donald Trump shut down the US Army Corps of Engineers Harbor and Tributary Study studying alternatives to protect the New York-New Jersey Metropolitan region from future disastrous storm surges. In the absence of this study, there is now no clear strategy to prevent recurrence of the devastation caused by Super Storm Sandy in October 2012.

Before it was cancelled, the Army Corps’ study was investigating several alternative strategies: the first two were a regional system of off-shore barriers with sea gates built as far as possible away from densely developed areas and the rest were a network of on-shore, “perimeter” barriers. However, the Corps’ study was not designed to address sea level rise, which was a major oversight and deficiency. Further, it did not adequately consider the economic disruption that future storms would have on the region. Also, it did not provide for a process to reconcile different stakeholders’ views on how best to proceed.

In the absence of a regional strategy, the cities of New York and Hoboken are planning their own systems of shoreline barriers. When they were first proposed soon after Sandy, these projects were supposed to be fast, cheap and effective. As it turns out, virtually none of them have been completed, most are mired in controversy, cost overruns and delays, and many are proving to be of questionable effectiveness. New York City’s proposed shoreline barrier system, first proposed in 2013 for an initial $4 billion outlay, is now projected to cost in excess of $50 billion. Virtually none of this has been built almost seven years later.

Storm surges and sea level rise are regional challenges requiring regional solutions. And we need a combination of both kinds of barriers: a hybrid, or layered system of off-shore movable sea gates to protect the region from infrequent but devastating extreme storm surges and a network of low shoreline barriers, raising streets or other measures to protect low-lying communities and critical infrastructure from spring tides, less severe coastal storms and sea level rise. And while a third kind of system – networks of preserved or restored natural systems, including oyster beds or wetlands – can improve water quality and ecological health and mitigate wave action, they will be simply overwhelmed by future severe storm surges. Finally, residents of some isolated, low-density coastal communities outside the proposed barrier system that are subject to repeated inundations will need to be relocated to higher ground.

Off-shore barriers with sea gates are an essential component of a comprehensive protection plan. Here is why critics' various objections should not stop New York, New Jersey and the federal government from building such a system.

Time and expense: Critics have argued that these systems cost too much and take too long to build. The Army Corps currently estimates that the most extensive off-shore barrier and gate system – one stretching from Sandy Hook in New Jersey to Breezy Point in Queens, accompanied by a smaller barrier across the north end of the East River near where the Throgs Neck Bridge crosses from the Bronx to Bayside, Queens. – would cost $63 billion and take 25 years to build. Although 50% lower than its initial $119 billion estimate, this estimate is still far in excess of what similar barriers have cost in other world cities. And their estimate assumes a far longer construction period than it should – the Army Corps built New Orleans’ post-Katrina barrier system in less than 5 years. Infrastructure does cost more to build in New York and other US cities than in their world city counterparts, due to onerous permitting and procurement procedures and outdated work practices. But these can all be addressed, as they were when Gov. Andrew Cuomo insisted on expediting construction of a new Tappan Zee Bridge. We can use these same expedited, and lower-cost, procedures to build this sea gate system. In any event, this expense is much less than the cost of repeated devastation from storms like Sandy, which caused at least $65 billion in damages. With expected sea level rise, future storms will occur more frequently and do much more damage.

The alternative protective barrier, which is on-shore perimeter systems, are also proving to cost far more and take more time to plan and build than originally proposed. Compared to onshore barriers, an offshore system will have far fewer complications with existing infrastructure and community concerns.

Dependability: Critics have argued that these systems aren’t dependable. Although an offshore barrier system would have multiple mechanically-operated gates, these employ proven marine engineering technology. Such systems in St. Petersburg and London have worked reliably. On the other hand, shoreline perimeter systems rely on manually operated gates, with sometimes hundreds or thousands of “deployable” components, all of which must be installed, maintained and activated by multiple agencies and private contractors yet to be determined or coordinated.

Impacts on water quality: Critics have argued that sewage will overflow into the harbor and backup when sea gates are closed during storm surges. There may be some sewage overflow, but gates would be closed at low tide prior to the arrival of storm surges, allowing the city’s combined storm/sanitary sewer outfalls to remain above water and function properly. With shoreline barriers, incoming surges would shut tide gates on sewer outfalls, causing sewage mixed with rain to back up into city streets and basements, unless costly investments are also made to improve drainage and to store sewage and stormwater underground during the storm. 

Impacts on tidal flows, fisheries and other environmental systems: Off-shore gates will adversely impact these systems to some extent. Great care must be taken to understand and mitigate those impacts in designing a system to prevent catastrophic flooding of the region. Recent high-resolution hydrodynamical modeling studies are showing that a well-designed system of movable sea gates would only minimally impact tidal flows and flushing in settled weather. London’s 40-year-old Thames River Barrier, with its movable gates, has helped the river become cleaner and healthier than it has been in more than a century. The British government is in the early discussion stages for an even larger Thames barrier several miles downstream from the current one, to protect an even greater portion of the region from more severe future storm surges.

Impacts on storm surge levels outside the barriers: Computer models developed by Stony Brook University and others have determined that when closed during a major storm, a sea gate system would increase storm surges along the Atlantic shore by just 3 inches or less and in western Long Island Sound by no more than 5 inches east of the Throgs Neck barrier.

What about the remainder of the region outside the barriers? Offshore barriers will protect the great majority of the region: one design, the Outer Harbor Gateway would protect 90% or more of the metropolitan region’s flood-prone populated areas from storm surges, including vulnerable low-income and minority communities such as the Rockaways, Red Hook, Coney Island, Newark, Elizabeth and Bayonne. Additional smaller barriers will be needed on Long Island’s south shore and the Connecticut shoreline, but these would not conflict with the Outer Harbor Gateway. 

How could we finance the massive investments required? The federal government usually pays for 60% of the cost of major flood prevention programs like this one, with state partners providing the remaining 40%. In this case, the states of New York and New Jersey would be the local partners. One possible source of state financing would be to capture the value of rapidly increasing premiums property owners have to pay for federal flood insurance. These payments would no longer be required once flood prevention measures are in place, so property owners could be taxed an equivalent amount to pay for the state share of debt service on the project. An alternative would be to capture a small portion of the increase in property values of real estate that would result from enhanced property values behind these barriers.

Storm surges and sea level rise threaten the future survival and well-being of the New York City metropolitan region. The region’s infrastructure also took a terrific beating from Sandy’s storm surge, from which we still haven’t fully recovered. Flooded subway and roadway tunnels and stations, power stations and sewage treatment plants were put out of service for weeks following the storm – and some, like Amtrak’s Hudson River Tunnels and the Long Island Railroad’s East River tunnels still await repairs nearly a decade later.

In addition some of our most treasured cultural and recreational assets, such as the Statue of Liberty, Ellis Island, Hudson River Park and others, were seriously damaged by Sandy, and would be threatened by future storms.

Storm surges are regional threats requiring regional, not local, solutions. A system of layered defense like the ones described here would protect the region for the next 100 years or more and give the region time to plan for even more profound climate changes that may emerge later in this century. We can’t be certain how much sea level rise will occur over the next century. But what we can do is to utilize the best scientific forecasts – which project six feet of sea level rise by 2100 – and design a layered defense system that will function with this or even greater increase. In any event, if we wait to be certain about these forecasts, it may be too late to protect the city and region from storm surges that we know will be coming. In the absence of the Army Corps’ flawed study, New York and New Jersey could follow how Texas endeavored to protect the Houston-Galveston Bay region from similar threats to those facing New York. The state of Texas funded an engineering study by Texas A&M University of alternatives to protect the region and had engineering consultants prepare schematic designs and preliminary cost estimates for this project and the study’s recommendations were then accepted by the Army Corps.

Texas’ congressional delegation then used this study to secure initial federal funding to complete the design of the recommended alternative: the $30 billion “Ike Dike” – a system of layered defense similar to that being proposed for the New York region. Texas’ politicians may not believe in climate change, sea level rise or earmarks, but they do believe in taking action to prevent loss of life and damage to the Lone Star State’s economy. The Ike Dike hasn’t been built – but if it had, it would have prevented much of the flooding in Houston and Galveston Bay caused by Ike and subsequent storms.

If Gov. Andrew Cuomo and New Jersey Gov. Phil Murphy make this issue a priority, they could direct the Port Authority of New York and New Jersey to lead an engineering study and a stakeholder and civic engagement process to reach consensus on the right mix of off-shore and shoreline barriers needed to protect the region and its infrastructure. The Port Authority’s involvement would be altogether reasonable since its airports, seaports, PATH tracks, rail yards and tunnel portals are all endangered by rising tides and flood waters.

As an initial step in the process, or in the event that the Port Authority declines to lead on this issue, the region’s two public engineering schools – SUNY Stony Brook and the New Jersey Institute of Technology– could study alternative strategies to protect our region. Looking at the threats posed by both storm surges and sea level rise, the study should consider all the economic, social and environmental impacts of alternative mitigation strategies, with the goal of reconciling different stakeholders’ diverse viewpoints. 

With luck, a new administration in Washington will take this issue more seriously than the current one ever has. And the region’s congressional delegation could include funding for this project in whatever national infrastructure program that emerges in coming years. Hopefully, it won’t require the devastation and loss of life caused by another hurricane to cause the region and its elected officials to take action on this issue.

Bob Yaro
is a professor at the University of Pennsylvania Stuart Weitzman School of Design, is the former president of the Regional Plan Association and a member of the Metro NY-NJ-LI Storm Surge Working Group, a professional group formed to find solutions to the existential threats of storm surges and sea level rise facing the New York City metropolitan region.
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