Protecting Metro New York from Storm Surges and Sea Level Rise By Bob Yaro, Professor of Practice, University of Pennsylvania Former President, Regional Plan Association Adjunct Professor, School of Marine and Atmospheric Sciences, Stony Brook University January 2020 Later this spring, the United States Army Corps of Engineers will decide how to best protect the New York City metropolitan region from future storm surges and sea level rise. This decision will determine whether the region can avoid repetiti on of the kind of devastation and loss of life it experienced from Hurricane Sandy in 2012 for the next century or more. As climate change intensifies, this will become an even greater concern, since according to the New York Academy of Sciences, storm - ind uced coastal flooding will become even more severe and frequent in the decades to come. The Army Corps’ Harbor & Tributaries Study (or “HATS” to use the Army’s acronym) is investigating two alternative strategies: the first is a regional system of off - sho re barriers with sea gates; and the second a network of shoreline, “perimeter” barriers. In the absence of a regional strategy, the Cities of New York and Hoboken are pursuing their own systems of shoreline barriers. When these were proposed soon after S andy, these projects were supposed to be fast, cheap and effective. As it turns out, virtually none of these have been completed, most are mired in controversy, cost overruns and delays, and many are proving to be of questionable effectiveness. The reali ty is that 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 devas tating storm surges and a network of low shoreline barriers, street raisings, 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, like oyster beds or wetlands — can improve water quality and ecological health and mitigate wave action, they will not protect the region from even an inch of future severe storm surges. Finally, resident s 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. Critics of off - shore barriers with sea gates have made a number of arguments agai nst these proposals, while others have come to their defense. Here are the pros and cons of these arguments: 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 mos t 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 — would cost $62 billion and take 25 years to build. Although low er than its initial $119 billion estimate, this one is still far in excess of what similar barriers have cost in other world cities. And their proposal would also take far longer to build than it should — the Army Corps built New Orleans’ new barrier system in less than 5 years. In any event, this expense is much less than the cost of repeated devastation from storms like Sandy, which caused $65 billion in damages. Further, as noted above, on - shore perimeter systems are also proving to cost far more and take more time to plan and build than originally proposed. Finally, we’re still paying for Sandy’s impacts, including the need to repair flood - damaged subway and railroad tunnels.) With expected sea level rise, future storms will occur more frequently and do much more damage. Dependability Again, critics have argued that these systems aren’t dependable. The reality is that although an offshore barrier system would have multiple moving parts, the experience around the world over the past four decades is that these employ proven technology and are 100% reliable. Indeed, they are more reliable than shoreline perimeter systems, all of which must work, and which rely on both moving parts and hundreds or thousands of “deployable” components 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 back up into combined sewer overflows when sea gates are closed before and during storm surges The reality is just the opposite: Barriers would be closed at low tide prior to the arrival of storm surges, allowing the city’s sewage outfalls and combined storm / sanitary sewers to remain above water and function properly. In the absence of a barrier system, surges would cause sewage to back up in to city streets and basements because it cannot drain through outfalls that are under water. Impacts on tidal flows, fisheries and other environmental systems: The proposed off - shore barriers will impact a ll of these things, and great care must be taken to understand and mitigate those impacts in designing a system to prevent catastrophic flooding of the region. A well - designed system of movable sea gates would minimize restriction of tidal flows, sediment s and fisheries. London’s similar 40 - year - old Thames Barrier with its movable gates, has allowed the Thames River to become cleaner and healthier than it has been in more than a century. Indeed, given this history, the British government is planning 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. Coastal scientists have maintained that barriers would cause minimal additional flooding outside the proposed barriers. In fact, computer models developed by Stony Brook University and others have determined that when closed prior to and during a major storm, this sea gate system would raise wa ter levels in Western Long Island Sound by no more than 3 inches, and by a similar amount on the Atlantic shore. What about the rest of the region outside the barriers? Offshore barriers will protect most of the region: The proposed Outer Harbor Barrier w ould protect 90% or more of the metropolitan region from storm surges. And it would protect some of its most vulnerable low income and minority communities, in places like the Rockaways, Red Hook, Coney Island and Newark, Elizabeth and Bayonne. Additiona l smaller barriers may be needed on Long Island’s south shore and the Connecticut shoreline, but these would not be in any way inconsistent with the Outer Harbor barrier. Storm surges and sea level rise represent existential threats to the future wellbei ng of the New York City metropolitan region. These are regional threats requiring regional, not local, solutions. A system of layered defense like the one described here would protect the region for the next century or more and give the region time to plan for even more profound climate changes that my emerge later in this century. The Army Corps and the region urgently need to get moving on this important initiative if we are to prevent recurrence of the devastation wrought by Sandy. The Author is a membe r of the Metro NY - NJ - LI Storm Surge Working Group, an ad hoc group of scholars, engineers, planners and community leaders formed to find solutions to the challenges of storm surges and sea level rise facing the New York City Metropolitan Region