How to Manage the Risk?
An integrated approach to managing flood risk begins with the recognition that flooding is a natural process that cannot altogether be prevented.
New York City’s approach focuses on increasing public awareness of risks, particularly among people living in flood zones, and reducing the vulnerability of risk-prone individuals and communities. In addition, it includes creating multiple lines of defense to protect buildings and infrastructure, improving stormwater management, and collaborating with many parties from the public and private sectors to strengthen the city’s overall capacity to cope with and recover from periodic flooding.
Recognizing the complex and varied nature of flood risk in New York City in the aftermath of Hurricane Sandy, the City developed a comprehensive coastal protection plan that explores strategies ranging from short- to long term, from “hard” to “soft,” and from brick-and-mortar to policy. The Mayor’s Office of Recovery and Resiliency was created to implement the plan.
Taken together, these strategies – regulatory controls, land use management policies, surface and subsurface measures, protections for buildings and infrastructure, and environmental restoration – add up to a broad but deliberate, multidimensional approach to promoting flood-risk resiliency in New York City.
Agencies at all levels of government play roles in managing risk from flood hazards. Most guidance is issued at the federal level, with a number of state and local agencies coordinating to implement it at the local level.
FEMA’s NFIP offers flood insurance for property owners in the FEMA-designated 1 percent annual chance floodplain. In order to participate and maintain eligibility for the NFIP, New York City is required to adopt building codes that meet FEMA standards for floodplain management. All owners of property within the 1 percent annual chance floodplain who hold federally-backed mortgages must purchase flood insurance.
FEMA is implementing reforms to the NFIP that are mandated by the Homeowner Flood Insurance Affordability Act of 2014. These reforms repeal and modify certain provisions of the Biggert-Waters Flood Insurance Reform Act of 2012 that mandated insurance premium increases for many policyholders to more accurately reflect flood risk.
Many older buildings constructed before FEMA’s initial flood maps were issued are located in high-risk flood zones and are eligible for flood insurance policies with federally subsidized rates. The new law lowers the recent rate increases on some policies, prevents some future rate increases, and implements a surcharge on all policyholders. Property owners can qualify for reduced insurance premiums by bringing their building into full compliance with current standards for flood-resistant construction.
Insurance Research and Consumer EducationFor insurance to play the appropriate role in providing financial protection to individuals and businesses from climate risks, policyholders must be aware of the flooding risks they face and know exactly what coverage their insurance policies include and exclude.
To help New Yorkers understand their flood risk, the Center for NYC Neighborhoods, the Mayor’s Office of Recovery and Resiliency, and the Governor’s Office of Storm Recovery launched FloodHelpNY, a consumer education program and website. The program includes a public information campaign to build awareness about the changes to the FIRMs and what the changes mean in terms of flood risk and flood insurance requirements. The campaign emphasizes to policyholders that standard homeowners insurance and small business property policies do not cover damages caused by flooding. FloodHelpNY also produces a quarterly newsletter with flood risk and flood insurance information to help New York City residents stay up-to-date on changes, critical issues, and serves.
In addition, the Department of City Planning (DCP) provides Information Briefs and a Newsletter containing current research and analysis flood risk and mitigation topics. The Flood Insurance Brief provides information on flood insurance requirements and how premiums will increase over time. The Flood Resilient Construction Info Brief better educates New Yorkers on how mitigation investments can reduce flood insurance premiums.
The Mayor’s Office of Resiliency has also developed an outreach plan to improve education and awareness about NFIP for New York City residents and to encourage NFIP enrollment in the City. The outreach strategy includes on-going briefings, workshops, trainings, consumer materials, and continued coordination with FloodHelpNY to ensure residents are able to access information from multiple sources:
- Briefings with elected officials, city agencies, and key stakeholders will provide an overview of the flood insurance landscape in New York City and help to ensure that those who regularly communicate and interact with floodplain residents have information and resources on NFIP. This will also help to provide context and embed flood insurance materials into existing City programs that interact with residents, such as homeowner fairs.
- Through coordination with stakeholders, provide community workshops for residents in the floodplain about key information and resources on FEMA’s flood maps, background on flood insurance and flood insurance requirements, and connect residents with local professionals trained in flood regulations, and flood counseling services. These workshops will provide an overview of NFIP, but also allow individuals to ask property specific questions about their structure and NFIP policy.
- Active coordination with trade professionals, such as the real estate industry, to develop continuing education training, to ensure that professionals, especially those that interact with individuals living or purchasing property in the floodplain, have up-to-date information on flood insurance requirements and knowledge of the resources available to find the information.
- Through coordination with behavioral scientists, work to evaluate and update existing printed and electronic materials available in the City on flood insurance and flood risk to ensure that materials are reaching target populations and driving individuals to enroll in flood insurance and/or complete mitigation on their property.
Building off the RAND study, the City continues to research various tools and mechanisms to improve flood risk communication, flood insurance enrollment, and mitigation assistance within the City. Led by the Mayor’s Office of Resiliency, multiple city agencies—including DCP, Department of Housing Preservation and Development (HPD), Office of Management Budget (OMB), Mayor’s Office of Housing Recovery Operations (HRO), Department of Finance (DOF), NYC Emergency Management (NYCEM), and the Department of Buildings (DOB)—convene for a monthly NFIP working group to study and evaluate the feasibility of local programs and policies that might help to incentivize flood insurance enrollment and home mitigation throughout the City. Work includes assessing the New York City building stock and socioeconomic landscape to determine what mechanism might encourage action throughout the City.
Additionally, as part of the City’s efforts to increase flood insurance enrollment and communication on flood risk awareness, the Mayor’s Office of Resiliency is conducting research on innovative methods to improve resident knowledge of flood risk. Current research focuses on ways to improve the disclosure of flood risk and flood insurance requirements for properties being sold in or near the City’s floodplain.
New York City has implemented many types of controls to mitigate the risk of flooding, including requirements for construction, zoning, and water management.
The Construction Code
The New York City Department of Buildings (DOB), which is designated to serve as the City’s Floodplain Administrator, enforces Appendix G of the NYC Building Code, which prescribes standards for flood-resistant construction in accordance with federal mandates.
New and substantially improved residential structures located in the A-zones within the 1 percent annual chance floodplain must meet the following standards:
- Lowest occupied floor must be constructed above the design flood elevation (DFE).
- If an enclosed space exists below the DFE, it can only be used for parking, storage, and building access.
- Utilities must be elevated above the DFE or be designed so that water is prevented from entering and accumulating.
New and substantially improved non-residential structures located in the A-zones within the 1 percent annual chance floodplain may either meet the standards above or allowed to be dry floodproofed in accordance with ASCE 24. Dry floodproofing is not permitted in V-zones.
Basements are not allowed in either zone for residential structures.
New York City amended its Construction Codes in January 2013 to require that buildings in the 1 percent annual chance floodplain be elevated beyond the requirements of the National Flood Insurance Program (NFIP). “Freeboard” is the term used to refer to this additional height. This requirement applies to new construction and to buildings undergoing substantial renovation.
One- and two- family homes are now required to provide two feet of freeboard as an extra level of protection above base-flood elevation; most other than essential facilities are required to provide one foot of freeboard.
The added height increases the margin of safety to allow for uncertainties inherent in flood modeling and Flood Insurance Rate Maps, which are based on historical data. Because sea level elevations shown on those maps do not include projected sea level rise, the allowance for freeboard helps to keep structures above floodwaters as storm surge elevations increase.
Because freeboard reduces flood risk, FEMA provides substantial reductions in flood insurance premiums for structures that incorporate it.
NYC Local Law 48 of 2015
NYC Local Law 48 of 2015 (Law No. 2015/048) mandated that catch basins—storm drains or sewer grates that collect storm water— be cleaned and maintained annually instead of the previously mandated three-year cycle. If a non-functioning catch basin is found, it must be fixed within nine days.
NYC Local Law 172 of 2018
NYC Local Law 172 of 2018 (Law No. 2018/172) requires the City to produce maps showing areas of the city most vulnerable to increased flooding due to the anticipated effects of climate change and publish a long-term plan to prevent or mitigate such increased flooding.
The plan and maps will be updated at least every four years, and periodically as new modeling are available and as climate change projections are updated.
NYC Stormwater Resiliency Plan
The Mayor’s Office of Climate Resiliency, per NYC Local Law 172 of 2018, and in collaboration with City agencies, developed the Stormwater Resiliency Plan. The Stormwater Resiliency Plan outlines the City’s approach to managing the risk of extreme rain events. The plan commits to four goals that optimize emergency response to extreme rainfall events and ensure that future City investments manage this climate risk. Each goal includes supporting sub-initiatives.
- Inform the public about flood vulnerability from extreme rain;
- Update NYC’s flash flood response procedures to prioritize response in vulnerable areas;
- Advance policies that reduce urban flooding and research that informs future risk;
- Leverage stormwater investments to help manage future flood risk from extreme rain and sea level rise. Future investments can alleviate flooding throughout the city.
Land Use Management and Zoning Law
Municipal governments shape the way land is used through zoning, which determines the permitted size and use of buildings, where buildings are located, and the density of neighborhoods.
In New York City, the Department of City Planning (DCP) administers zoning law. Policy tools to manage flood risk can be applied at different scales, ranging from site-specific to local and regional.
Amendments to zoning law can facilitate investment in flood-resilient buildings by removing disincentives and restrictions to that prevent building owners from meeting or exceeding flood-proofing standards in the Building Codes. For example, the zoning law’s building height limitations were a disincentive for property owners in the flood zones to elevate their structures to reduce the risk of flooding. The zoning law was amended to remedy this.
New Neighborhood Special Districts
In 2017, New York City established Special Coastal Risk Districts in Broad Channel and Hamilton Beach in Queens, and in Oakwood Beach, Graham Beach, and Ocean Breeze on the East Shore of Staten Island.
The special districts place limits on the density and uses allowed within these areas, because these areas face exceptional flood risks. The special district in Staten Island was designated a buyout area by New York State. New development in this area now requires approval from the City Planning Commission.
New Citywide Zoning Text
The 2013 Flood Resilience Zoning Text Amendment encourages flood-resilient building construction throughout FEMA-designated flood zones by removing regulatory barriers that hinder or prevent the reconstruction of storm-damaged properties. This amendment also makes it possible for new and existing buildings to comply with new, higher building flood elevations required by FEMA and with new requirements in the New York City’s Building Codes.
DCP is currently in the process of refining and making this text amendment permanent. In addition, DCP is continuing to look at additional neighborhoods within the flood zone and to work with communities to identify zoning changes that will encourage more resilient buildings and reduce density in the most vulnerable areas.
Parks Flood-Resiliency Manual
New York City Department of Parks and Recreation (NYC Parks) created Design and Planning for Flood Resiliency: Guidelines for NYC Parks, a manual that guides development and renovation of coastally resilient waterfront city parks.
Climate Resiliency Design Guidelines
The Mayor’s Office of Resiliency (MOR) in collaboration with City agencies developed design guidelines that provide a consistent methodology to incorporate forward-looking climate data within the design of City infrastructure and buildings. These design guidelines help engineers, architects, landscape architects, and planners incorporate resiliency against sea level rise, extreme heat, and extreme precipitation events for a wide range of City facilities. This foundation guides City agencies on ways to use capital design to mitigate climate change risk. City agencies build upon this foundation by developing their own, more specific guidelines that fit the design criteria suited to their specific assets.
Flooding can be managed effectively by cleaning and maintaining drainage infrastructure, building out the sewer infrastructure, managing surface water run-off, employing green infrastructure, and providing floodwater storage.
Design and Construction of Stormwater Management Systems
New York City’s Department of Environmental Protection (DEP) is responsible for designing and developing the drainage plan for the city. DEP also governs and oversees the construction of private sewers and drains to ensure compliance and that drainage capabilities are adequate. DEP is pioneering sustainable stormwater management strategies, including Bluebelts and green infrastructure.
DEP’s comprehensive NYC Wastewater Resiliency Plandetails cost-effective strategies to reduce flood damage to wastewater infrastructure and safeguard public health and the environment. The plan examines 96 pumping stations and 14 wastewater treatment plants, identifying and prioritizing the facilities at risk of flood damage and presenting resiliency recommendations for them.
Sewers, Drainage, and Green Infrastructure
New York City is improving stormwater management by investing in sewer and drainage infrastructure to expand its capacity -- adding high-level storm sewers, improving pumping stations, installing backflow valves, and increasing the effectiveness of catch basin and storm drain maintenance.
New York City’s pumping stations convey millions of gallons of sewage from homes, businesses, hospitals, and numerous other sources to treatment facilities, helping to mitigate street flooding and ensuring sewage does not overflow into the street or back up into basements. Projects are currently underway to protect pumping stations and make them more resilient to service interruptions caused by flooding.
Certain parts of New York City do not have fully built-out storm sewer infrastructure, including the neighborhoods comprising Southeast Queens. DEP has committed over $2B to The Southeast Queens Flood Mitigation Plan, a project intended to alleviate upland flooding and improve the drainage and conveyance of stormwater. The plan consists of a four-pronged approach with many individual projects:
- “Quick fixes” based on 311 data of hardest hit areas. Project techniques include storm sewer extensions, green infrastructure, and “when & where” contracts.
- Build neighborhood sewers where street elevations allow them.
- Create future capacity by investing in trunk sewers which will allow for the future buildout of neighborhood sewers.
- Evaluate options to reduce basement flooding.
Preserving and/or Restoring Natural Drainage Corridors
Natural drainage corridors – including streams, ponds, wetland areas, parks, and open spaces – help convey, store, and filter stormwater. Sometimes referred to as “bluebelts,” these corridors are ecologically rich and cost-effective drainage systems that naturally handle the precipitation runoff from streets and sidewalks by preserving natural drainage corridors. For example, the Staten Island Bluebelt, an award-winning wetland preservation program, uses a network of streams, ponds, and other wetland areas to provide ecologically sound and cost-effective stormwater management for approximately one-third of the borough.
Temporary rainwater storage features can help alleviate floods, especially flash floods, when the rainfall rate exceeds the ground’s capacity to absorb the rain. Features, such as retention ponds and reservoirs, divert water away from vulnerable structures and infrastructure, allowing it to drain more easily.
Cloudburst Resiliency Planning StudyIn 2016, NYC DEP kicked off a Cloudburst Resiliency Planning Study to assess risks, prioritize response, develop neighborhood-based solutions, and assign costs and benefits to manage extreme rain events, or “cloudbursts,” using Southeast Queens as a focus area. The study adapted an approach developed in Copenhagen to manage large volumes of stormwater using streets and open space. By modeling the flow of floodwater over the local topography, the study is able to identify opportunities to slow and safely convey water so as to minimize damages and maximize co-benefits to the community. Working in coordination with DOT, the Department of Design and Construction (DDC), and New York City Housing Authority (NYCHA), DEP initiated two pilots in St. Albans and South Jamaica Houses in Queens. The projects will incorporate green infrastructure to reduce the impact of flash flooding by capturing 2-3 inches of rainfall per hour. |
Temporary rainwater storage features can help alleviate floods, especially flash floods, that occur when the rainfall rate exceeds the ground’s capacity to absorb the rain. Features, such as retention ponds and reservoirs, divert water away from vulnerable structures and infrastructure, allowing it to drain more easily.
Green Infrastructure
Green infrastructure allows water to infiltrate the ground more easily, reducing the volume of stormwater runoff that would otherwise have drained into the sewer system. Reducing the volume of water entering the sewer system can help to reduce sewer overflow and in some instances, minimize flooding, particularly if the green infrastructure is sized to manage more than a water quality storm event. Some examples presented below include green roofs and Right-of-Way green infrastructure practices.
Enhancing vegetation in densely developed areas and on rooftops can also lower the energy needed to cool buildings, lowering energy costs. Green roofs consist of vegetation growing in engineered soil that sits on top of a drainage layer. This type of rainwater capture and retention reduces the volume and flow of water flowing into city sewers.
In 2019, there were 736 green roofs in New York City, covering 60 of the 40,000 acres of rooftop space. City law requires new and substantially renovated or enlarged rooftops to incorporate sustainable roofing on all available roof space. Additionally, New York State provides a Green Roof Property Tax Abatement available for property owners installing green roofs and includes an enhanced abatement for select community districts designated by the City. DEP also provides funding for the design and construction of green roof implementation on privately owned existing buildings.
Green infrastructure constructed within the Right-of-Way (ROW) can absorb and manage stormwater runoff from streets and sidewalks to alleviate pressure on the sewer system that otherwise receives that flow. Since 2012, DEP has constructed over 10,000 green infrastructure practices, including rain gardens and infiltration basins, within NYC’s ROW. Building upon recently completed porous pavement pilots, DEP is also expanding the amount of porous pavement constructed within NYC streets.
Green streets and pedestrian plazas increase public spaces and reduce impervious surfaces. NYC Parks and DOT have partnered to add green spaces to rights of way and build over 2,500 green streets. Some include converting underutilized street spaces into pedestrian plazas, moving streets into the public realm, and reducing impervious surfaces where possible.
Water Conservation and Reuse
Water conservation and reuse primarily conserve potable water, but it also offers the benefit of reducing the burden on the sewer system and wastewater facilities. DEP currently promotes water conservation and reuse through the “Wait…” program, which notifies participants when to use less water during a heavy rainstorm to protect sewer and drainage infrastructure. DEP also funds water conservation and reuse as part of the Water Demand Management Program, which includes municipal partnerships and a Water Conservation and Reuse Grant Pilot Program for private properties.
Many strategies are used in New York City to make buildings more flood-resistant.
The DCP’s Retrofitting Buildings for Flood Risk Design Manual analyzes and illustrates retrofit design options for ten real-world examples representing New York City’s vulnerable building typologies. The manual serves as a resource for a variety of public and private-sector parties, including policy makers, architects, engineers, builders, developers, and property owners.
The examples presented in the manual guide depict users on current regulations as well as offers alternatives for mitigating buildings that are not substantially damaged or need substantial improvements. By offering practical solutions to retrofit properties in the flood zone, the manual advances New York City’s climate adaptation goals.
Recommended actions include the following:
- Dry floodproofing -- using watertight construction methods, such as the installation of temporary shields or barriers, that keep water out of a building. Site protection can also be accomplished with deployable or permanent floodwalls, or a berm (an earthen mound), outside a building or around the site’s perimeter.
- Wet floodproofing -- constructing or retrofitting buildings with materials that resist flood damage yet allow water to freely flow in and out without causing significant damage.
- Building elevation -- raising a building so that the lowest floor is above the design flood elevation, which is equal to the height of a 1 percent annual chance flood at a given location plus a safety margin for freeboard.
- Equipment elevation - elevating mechanical equipment above the design flood elevation by either moving it to a higher floor, placing it on a raised platform, or suspending it from an overhead structure. For example, high-rise buildings can employ a system to prevent elevators from descending into floodwaters.
- Land and street elevation -- a strategy that works best on large development sites or at a neighborhood scale, where lots and streets can be raised in a coordinated manner. In New York City, Arverne By The Sea, a 117-acre development on the Rockaway Peninsula, was elevated approximately 5 feet prior to construction, and experienced significantly less flooding during Hurricane Sandy than surrounding areas.
Protecting critical infrastructure against the risk of floodsinclude infrastructure assets such as subway entrances and tunnels, electricity and steam generation facilities, gas, and steam distribution systems, water supply systems, wastewater treatment plants, healthcare facilities, and other facilities housing vulnerable populations.
Strategies to protect infrastructure from damaging floods vary widely depending on the type of infrastructure, and can range from floodproofing or elevating individual facilities and equipment to implementation of larger operational or design changes. Examples for different types of infrastructure include:
Case Study: NYU Langone Medical CenterThe main campus of NYU Langone Health, a key emergency facility along the East River, was severely damage by Hurricane Sandy and forced to close for nearly two months. NYU Langone has rebuilt and made a significant investment in a flood-protection system that is designed to protect all of its main campus buildings from storm surge inundation up to and beyond that experienced during Hurricane Sandy. NYU Langone elevated all of its critical infrastructure (electrical transformers and emergency power generators) to ensure that it remains operational in the unlikely event that floodwaters penetrate the flood-protection system. The most significant flood-mitigation investment is its new Energy Building, which combines a heat and power (CHP) plant with redundant backup emergency power and fuel oil. This enables the main NYU Langone campus to be self-sufficient if there is an interruption in power from the utility. These systems work together to protect the critical building systems and specialized equipment at the Main Campus. |
- Subways: Elevating air vent gratings over subways, so floodwaters cannot enter the system.
- Tunnels: Improving pumping capacity in subway, commuter train, and passenger car tunnels.
- Subway and rail: Raising or dry floodproofing track switches and electrical equipment.
- Power plants: Improving redundancy in the power supply by increasing the number of power supply feeders, installing additional distribution transformers, and building new substations outside of flood-prone locations.
- Hospitals: Elevating electrical equipment and ensuring emergency backup power in hospitals.
Projects to protect New York City's critical infrastructure systems from flooding are being undertaken by many agencies such as NYC DEP, DOT, the Health and Hospitals Corporation (H+H), the Metropolitan Transportation Authority (MTA), and the Port Authority of New York and New Jersey (PANYNJ). Participation from utility providers, such as Con Edison, National Grid and PSEG/LIPA, has served to increase the number of joint initiatives markedly since Hurricane Sandy.
New York City stakeholders continue to research solutions in case higher sea levels and increased flooding become more commonplace in the future, such as:
- Structures that float at all times and are designed to move vertically with tidal fluctuations and storm surge. Unlike houseboats, these structures lack motoring and steering capabilities and cannot move through water on their own. Utility connections are flexible, allowing the structure to move naturally with the water. Floating structures are rare in New York, and are effectively prohibited. These solutions, however, are already in operation in the Netherlands, Germany, and Australia and in the United States in Sausalito, California; Portland, Oregon; and Seattle, Washington.
- Amphibious structures that are built on dry land but use their buoyant foundations and pile supports to float if a site is flooded. A few amphibious homes have been constructed in Louisiana and the Netherlands.
Prior to Hurricane Sandy, New York City implemented structural solutions to protect flood-prone properties. Post-Sandy, these initiatives have expanded to include integrated flood protection systems, increased coastal edge elevation, and protection of infrastructure and critical services.
Studies, funded with federal and state recovery funds, have evaluated which coastal protection measures are best suited to the unique vulnerabilities of specific New York City sites and neighborhoods. In New York City, two types of coastal defense strategies are considered:
Bulkheads or Seawalls
Bulkheads are usually made of stone, concrete, or steel, hold soil in place, and stabilize the shoreline to resist the forces of erosion. These hard structures are not typically designed to prevent flooding from storm surge associated with a coastal storm; instead, they are designed to work with everyday tidal fluctuations, currents, and wakes.
Many stretches of the Upper Bay and Hudson shoreline have been bulkheaded since the early 20th century. Today, bulkheads are located along the New York City’s waterfront, protecting industrial areas, commercial and residential areas, and parkland. Approximately 25 percent of New York City’s shoreline is protected by bulkheads.
Levees
Levees, also called dikes, are earthen embankments built at the shoreline to protect land from flooding. Levees are commonly used throughout the country along riverbanks. In the Netherlands, multipurpose levees – levees that incorporate public transit, highways, buildings, and parks on top of or within the structure – are used in combination with surge barriers along the Dutch coastline.
Floodwalls
Floodwalls are permanent or deployable vertical structures anchored in the ground either at the shoreline or upland to prevent flooding from rivers or storm surge. Permanent floodwalls are sometimes used on top of, or as an extension of, a levee to add protection where there is not enough land for a levee, such as the case in New Orleans. Some floodwalls are built with gates to provide access to a roadway or other right-of-way. Floodwalls with gates are designed so that they can be closed in advance of a flood.
Deployable floodwalls are installed to prepare for a flood event. They can be inserted into permanent ground fixtures or vertical posts. Most deployable floodwalls require human installation, but some are designed to rise automatically in response to flood .
In-water Surge Barriers
Surge barriers are typically used in combination with larger flood protection systems that include levees, floodwalls, and pumps. These structures provide a high level of protection from storm surge. Under normal conditions, surge barriers remain open, allowing water and vessels to pass, but the barriers can be closed when water levels rise due to storm surge. All surge barriers require extensive maintenance and monitoring.
Although a few surge barriers are found across the East Coast of the United States, none currently exist in New York City. However, in the aftermath of Hurricane Sandy, their feasibility was studied for areas such as Gowanus, Newtown Creek, and Coney Island.
NY-NJ Harbor and Tributaries Coastal Storm Risk Management Feasibility StudyThe US Army Corps of Engineers is conducting a study, NY-NJ Harbor and Tributaries Coastal Storm Risk Management Feasibility Study. The purpose of this work is to manage the risk of coastal storm damage in the New York and New Jersey Harbor and tributaries (NYNJHAT) study area and to contribute to the resilience of communities, critical infrastructure, and the environment. Coastal defenses that are being evaluated included levees, flood walls, bulkheads, and storm surge barriers. |
Four Case Studies: Hard Structure Coastal Defense
Interim Flood Protection Measures (IFPM)
Because long-term flood mitigation projects requirelong implementation periods, the NYC Emergency Management (NYC EM), in coordination with the Mayor’s Office, initiated the IFPM program to protect neighborhoods and critical facilities from low-impact, more frequent flooding events until permanent flood-reduction projects are completed. IFPM includes installing flood-control protections such as Tiger Dams (long tubes filled with water), HESCO barriers (large sand-filled geotextile containers), and flood logs (stackable barriers that can be used to close up doorways and other flood entry points). This project’s current portfolio includes 40 city facilities and two neighborhoods.
East Side Coastal Resiliency (ESCR) Project
Since Hurricane Sandy, New York City initiated an integrated flood protection system on the east side of Manhattan from East 25th Street to Montgomery Street. This project aims to protect the East Side against flooding and sea level rise, provide access to public spaces, and protect thousands of people living in public housing. Part of this project includes a system of walls, deployables, and berms (raised land to protect or separate low-lying areas from adjacent water bodies) along between the FDR Drive, and the East River Park, and Stuyvesant Cove Park. ESCR’s final design is expected to be completed by 2019.
Lower Manhattan Coastal Resiliency (LMCR) – Two Bridges
New York City will continue the flood protection strategies for the coast of Manhattan’s Lower East Side by designing and building a flood protection system from Montgomery Street to the Brooklyn Bridge. LMCR activities are still in the design phase.
Lower Manhattan Coastal Resiliency (LMCR) -- Manhattan Tip
New York City is currently working on designs to protect Lower Manhattan’s tip from storm surge, flooding, and rises in sea level. Part of this initiative includes a long-term study of climate risks (storm surges, sea level rise, groundwater table rise, increased precipitation, and extreme heat) in 2100.
Some of the potential trade offs of hard based shoreline structures include lack of access to waterfront recreational areas, loss of wildlife habitat, and a higher risk of coastal erosion. Since Hurricane Sandy, New York City is exploring how natural and nature-based structures and systems can be integrated into coastal defense strategies alongside the hard-structure approach.
Some natural protective features such as wetlands, dunes, and vegetation naturally absorb energy from storm surge and waves, providing varying degrees of protection for structures located behind them. Following are examples of some natural and nature-based strategies:
Living Shorelines
Living shorelines are engineered buffers based on natural systems. This bank stabilization technique combines plants, sand and/or soil, and minimal hard infrastructure to protect the shoreline. The advantage of this approach is to help reduce erosion and to maintain and protect valuable intertidal habitats and coastal vegetation.
Living shorelines can attenuate wave action and buffer against storm surge by breaking waves before the waves reach the shoreline and endanger adjacent neighborhoods. It will also be used to limit the effects of sea level rise.
Case Study: Tottenville Living Breakwaters
Tottenville Living Breakwaters: Tottenville is an innovative coastal infrastructure project designed to reduce or reverse erosion and damage from storm waves, improve the ecosystem health of Raritan Bay, and encourage stewardship of nearshore waters. The New York State Governor’s Office of Storm Recovery (GOSR) is planning a breakwater project in Tottenville on the South Shore of Staten Island. |
Wetlands
Wetlands, which use plants and soils to retain and filter water, are important wildlife habitats in New York City. Large wetlands use friction to help slow the rate of storm surge, and in some cases reduce flood heights. The degree to which wetlands offer an opportunity to reduce flood risk depends upon the storm’s speed and intensity and the size of the wetland. Flooding can even enhance the natural health and functionality of wetlands.
In New York City, the numerous benefits of wetlands have prompted the creation of constructed wetlands in which hard infrastructure protections are combined with ecological enhancements.
Beaches, Beach Nourishment, and Dunes
Beaches, beach nourishment, and dunes are three natural and nature-based protective features that function as sandy buffers, helping to protect shorelines from the destructive impact of strong waves and flooding. These natural features are sometimes reinforced with vegetation, geo-textile cores, or an enginnered core made up of stone or steel.
Beach nourishment is the process of replenishing sand or depositing it on beaches to increase the elevation and distance between upland areas and the shoreline. Collectively, sand dunes act as a buffer to dissipate storm wave energy and block rising water from inundating lower-elevation areas.
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