Flash flooding is the number one cause of deaths associated with thunderstorms, claiming more than 140 lives each year.

Flash floods can strike any time with little or no warning. City streets can become rivers in seconds. Most flash flooding is caused by slow-moving thunderstorms, thunderstorms repeatedly moving over the same area, or heavy rains from hurricanes and tropical storms. Blocked catch basins, storm drains, water main breaks, and sewer lines can also lead to flooding.
Read more about flash flooding causes from the NYC Department of Environmental Protection

Flash Floods and NYC

Much of New York's infrastructure — particularly low-lying and poor drainage areas — cannot cope with rainfall of more than one inch per hour.

On August 8, 2007, a severe rainstorm accompanied by an EF2 tornado brought three inches of rain in two hours to New York City and flooded streets and subways, shutting down service for several hours.

In January 1999, several Queens residents were evacuated due to flooding from a record rainstorm. Water rose waist-high in parts of Springfield Gardens and foot-deep water on the JFK Expressway halted traffic for more than two hours.

In October 1996, a major rainstorm deluged the City and parts of New Jersey with up to 8.6 inches of rain, killing four people and cutting power to 341,000 homes in New York, New Jersey, and Connecticut. Homes were flooded in Springfield Gardens, Queens, Edgewater Park in the Bronx, and the Sea Gate and Gerritsen Beach sections of Brooklyn.

National Weather Service Terms

FLASH FLOOD WATCH: Issued when it is possible rains will cause flash flooding in a specified area.
FLASH FLOOD WARNING: Issued when flash flooding is occurring or is imminent in a specified area.

Flash Flooding Risks

STREET FLOODING

Significant street flooding can pose risks to both pedestrians and drivers.

• Avoid walking through moving water.
  • 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.
• Do not drive into flooded areas.
  • Six inches of water will reach the bottom of most passenger cars, causing loss of control and possible stalling.
  • A foot of water will float many vehicles.
  • Two feet of rushing water can carry away most vehicles, including sport utility vehicles (SUVs) and pick-ups.
    
• Stay out of any building if it is surrounded by floodwaters.

SEWER BACK-UPS (SBUs)

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. Sewage contains germs that may cause stomach or intestinal infections if swallowed. It also may infect a cut on the skin or other open areas, such as the eyes. Children, pets, and people with compromised immune systems should stay away from floodwater and anything it has touched until the area has been cleaned and disinfected.

If New Yorkers see sewers or manholes that are overflowing in the city, they should call 311 (TTY: 212-504-4115) to report the location.
Watch a simulated SBU
See an illustration of an SBU

Reduce Your Risk

The New York City Department of Environmental Protection (DEP) illustrates how the City's sewer system manages rainwater, and offers residents and business owners methods to reduce flooding. OEM offers several, non-sewer-related steps New Yorkers can take to reduce their risk of flooding.

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 SPACE

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.

FLOOD INSURANCE 

Cleaning After the Flood

BASIC CLEAN-UP TIPS

• 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.

If the flood water contains sewage, it is important to disinfect all contaminated items. Disinfect by wiping surfaces with a bleach solution. Use a half cup of household bleach for one gallon of water.  Non-bleach sanitizers can also be used, although you must follow the manufacturers’ instructions.

Warning: Bleach may damage some materials. Never mix bleach with ammonia or detergents containing ammonia products. Dangerous gases may be created.

• Discard any food items, including packaged food, that was in contact with sewage water.
• Avoid direct contact with sewage.Be careful not to splash sewage onto your face. Wear waterproof gloves and boots.
• Wash your hands, body and clothing with soap and water after cleanup.

For floors, wooden furniture, and other wooden surfaces containing sewage:

• First, remove visible contamination with detergent and water.
• Second, disinfect by wiping surface with a bleach solution. Non-bleach sanitizers can also be used, although you must follow the manufacturers’ instructions.
• Third, allow surfaces to dry thoroughly to avoid mold growth.

For clothing, bedding, and other porous items:

• Normal laundering with detergent will disinfect most items. Pre-rinsing with cold water can prevent staining. Dry thoroughly.
• Most waterproof boots and gloves can be disinfected with bleach solution. Use a half cup of household bleach in one gallon of water. Then rinse and allow to dry.
• Dry cleaning will generally disinfect clothing.
• Leather shoes may be difficult to disinfect, if soaked it may be best to discard them.
• Valuable paper items and photographs may require cleaning by a professional trained in conservation methods.

For rugs and carpeting:

• Small areas may be cleaned in place using detergents and disinfectants.
• Always dry thoroughly and quickly.
• Larger areas should be cleaned by a professional.
• Discard soaked rug padding.

For more information on safety issues related to flood recovery, use the flood fact sheets provided by the U.S. Center for Disease Control and Prevention or call (800) CDC-INFO.

 PREVENT MOLD GROWTH

• Dry all areas and items quickly and thoroughly.
• If it has stopped raining, open windows to circulate fresh air.
• Use fans to help dry out your home and reduce odors.

Warning: Do not run any electrical equipment or appliances near standing water.

• If available, use a dehumidifier to help dry out enclosed spaces.
• If it is necessary to dispose of standing water, use a portable submersible sump pump and/or a wet dry vacuum.
• Extensive flooding damage may require cleanup and restoration by professionals.

For more information on cleaning mold and mold health effects visit the NYC Department of Health and Mental Hygiene online.