Coastal flooding occurs when intense, offshore low-pressure systems drive ocean water inland. The water pushed ashore is called storm surge. Coastal flooding levels — categorized as minor, moderate, or major — are calculated based on the amount water rises above the normal tide in a particular area.
Minor flooding is nuisance coastal flooding of locations adjacent to the shore. Minor beach erosion can occur. Minor coastal flooding is not expected to close roads or do any major structural damage to homes and other buildings.
Moderate flooding is more substantial coastal flooding, threatening life and property. Some roads may become impassable due to flooding. Moderate beach erosion will occur along with damage to some homes, businesses, and other facilities.
Major flooding is a serious threat to both life and property. Numerous roads will likely become flooded. Many homes and businesses along the coast will receive major damage. People should review safety precautions and prepare to evacuate if necessary. Major beach erosion is also expected.
Tidal flooding occurs when the tide's range is at its highest level (also called a spring tide), but it can also occur with no storm.
Riverine flooding occurs when freshwater rivers and streams overflow their banks.
Blocked catch basins, storm drains, water main breaks, and sewer lines can also lead to flooding. Surcharged sewers/sewer backups also can lead to flooding. Sewage is carried in different pipes than those for drinking or washing water. Unless otherwise notified, it is safe to drink tap water in an area with flooding; however, floodwater from SBUs can pose serious health risks.
Storm surge is an abnormal rise of water generated by a storm, over and above the predicted astronomical tide, and accounts for the largest number of hurricane fatalities. A major hurricane could push more than 30 feet of storm surge (the height of a three-story building) into some parts of New York City, and storm surge can travel several miles inland. Storm surge and large battering waves can endanger lives, destroy buildings, erode beaches and dunes, and damage roads and bridges. Storm surge can occur several hours before the hurricane itself makes landfall. It can also take place after a hurricane has moved away from the city, as high seas slump back into confined spaces like Long Island Sound.
Large areas of southern Queens, southern Brooklyn, the lower east and west sides of Manhattan, and the perimeter of Staten Island could all suffer damage from a hurricane's storm surge. In addition, storm surge from a strong hurricane would not be limited to waterfront properties and could conceivably push miles inland in some areas. New York City's unique geography — located at a "bend" in the coastline between New Jersey and Long Island called the "New York Bight" — makes it especially vulnerable. New York Bight will guide storm surge directly into New York City, amplifying flooding and related damage. Even a low-level hurricane that makes landfall near New York City could wash ocean waters over large sections of some coastal neighborhoods.
Flash Flood Watch: issued to indicate current or developing hydrologic conditions that are favorable for flash flooding in and close to the watch area, but the occurrence is neither certain or imminent.
Flash Flood Warning: issued to inform the public, emergency management, and other cooperating agencies that flash flooding is in progress, imminent, or highly likely.
Coastal Flood Watch: issued by the National Weather Service when coastal flooding is possible within 12 to 36 hours.
Coastal Flood Warning: issued by the National Weather service when coastal flooding is occurring, imminent, or expected within 12 hours.
In June 2013, FEMA Region II released preliminary revisions to New York City flood zones as a result of a new coastal flood study to update the information shown on the Flood Insurance Rate Maps (FIRMs). As the next step in the flood map update process for New York City, FEMA will be issuing Preliminary FIRMs and a Preliminary Flood Insurance Study (FIS), a narrative report of a community's flood hazard. These maps and study are the official version of the Preliminary Work Maps that were released in June 2013, and will go through a public review and comment period as well as an official appeals period. For more information on FEMA's flood map update process, visit NYC.gov/floodmaps.
Consider getting flood insurance. Protection against loss due to floods is not covered under a homeowner's policy. Contact your property/casualty agent or broker about eligibility for flood insurance. For more information, visit the National Flood Insurance Program online at www.floodsmart.gov.
Make an itemized list of personal property, including furnishings, clothing, and valuables.
Fill out an Emergency Reference Card, which will contain important contacts for you and your family in the event of any emergency.
Prepare a Go Bag that you can grab in case you need to leave your home in a hurry.
Learn the safest route from your home or workplace to safe, high ground in case you have to evacuate. This should be part of your household disaster plan.
If you live in a flood-susceptible area, keep materials, such as sandbags, plywood, plastic sheeting, and lumber, on hand to help protect your home.
Stay informed. Before and during an emergency, the City will send emergency alerts and updates to New Yorkers through various channels.
Depressed driveway protection: If your property has a driveway that slopes below street level, the City recommends you contact a contractor to help prevent flooding into your basement. Obtain two or three quotes from different contractors before beginning the work, as the job can vary widely in price depending on various field conditions.
Green spaces, trees, and plants absorb rain water and prevent it from collecting and pooling on concrete surfaces. When possible, plant vegetation and avoid paving over green space. If you identify a good area for a tree in your neighborhood, visit www.milliontreesnyc.org, to request a tree from the New York City Department of Parks and Recreation.
Know What to Do During a Flood
Keep a battery-operated AM/FM radio tuned to a local station and follow emergency instructions.
If it is safe to evacuate, take your Go Bag with you.
If you're caught inside by rising waters, move to a higher floor. Take warm clothing, a flashlight, and portable radio with you. Wait for help. Do NOT try to swim to safety.
When outside, avoid walking and driving through flooded areas. As few as six inches of moving water can knock a person over. Six inches of water will reach the bottom of most passenger cars, causing loss of control and possible stalling. One or two feet of water can carry away a vehicle.
Water may be contaminated by oil, gasoline, or raw sewage.
Water may be electrically charged from underground or downed power lines. Stay away from downed power lines, and report them to the power company.
If you have to walk in water, walk where the water is not moving or use a stick to check the firmness of the ground in front of you.
Stay out of any building if it is surrounded by floodwaters.
If time permits:
Turn off all utilities at the main power switch and close the main gas valve if evacuation appears necessary. Do not touch any electrical equipment unless it is in a dry area, or you are standing on a piece of dry wood while wearing rubber-soled shoes or boots and rubber gloves.
Fill bathtubs, sinks, and jugs with clean water in case regular supplies are contaminated (you can sanitize these items by first rinsing with bleach).
Board up windows or protect them with storm shutters or tape (to prevent flying glass).
Bring outdoor objects, such as lawn furniture, garbage cans and other loose items, inside the house or tie them down securely.
Know What to Do After the Flood
Before re-entering a building, check for structural damage. Make sure it is not in danger of collapsing. Turn off any outside gas lines at the meter or tank, and let the building air out for several minutes to remove foul odors or escaping gas.
Watch for electrical shorts or live wires before turning off the main power switch. Do not turn on any lights or appliances until an electrician has checked the system for short circuits.
Cover broken windows and holes in the roof or walls to prevent further weather damage.
Throw out fresh food and previously opened medicines that have come in contact with floodwaters.
New York City tap water is safe to drink, including in areas with flooding, unless otherwise reported by City officials. If your water service was disrupted run the tap for at least 30 seconds and until the water runs cold and clear. Replace all ice machine filters and beverage dispenser filters, and flush all water lines for five minutes. Monitor NYC.gov/dep for any updates on NYC drinking water.
Assessing and Repairing Damage
Owners who want to reoccupy residences damaged by flooding should first hire a New York State-licensed Registered Architect or Professional Engineer to assess the building's safety. If the building is not safe to occupy, the owners should seek alternative housing arrangements while repairs are made. Owners should take pictures of all damage and flood impacts and keep receipts for all repairs if they intend to apply for disaster assistance or to make an insurance claim.
To make repairs, owners need to work with an engineer or architect who has the necessary City-authorized permits. The City advises residents to obtain two or three quotes from different contractors before beginning the work, which can vary widely in price depending on various field conditions. If an owner needs assistance with applications for permits, he or she should contact 311 (212-639-9675 for Video Relay Service, or TTY: 212-504-4115).
Dry all areas and items quickly and thoroughly.
Dryclean or wash and dry all clothing and other home items. Clean floors, furniture, and other surfaces with detergent and water.
Stay out of deep water. Extensive flooding damage may require clean-up and restoration by professionals.