A flash flood can rise in minutes, often with little warning, and most flood deaths happen when people try to drive or walk through moving water. Knowing what to do before the water arrives, and what to avoid once it does, is the most effective protection. This guide sets out how flash floods happen, how to prepare, and the safety rules that apply during and after one.
What a flash flood is
A flash flood is a sudden rise of water over ground that is normally dry. It can follow heavy rain, a dam or levee failure, or a sudden release of water upstream. Floods of this kind are fast, so there may be little time to react, and the danger is greatest near rivers and in steep valleys where water moves quickly.
Flooding is not limited to areas near rivers. Ready.gov notes that flooding does not follow lines on a map, and that it can happen wherever it rains heavily. Checking your risk matters even if you have never flooded before.
Before a flood: know your risk and your warnings
- Check your flood risk. FEMA’s Flood Map Service Center shows the flood risk for an address. Ready.gov recommends using it to understand the types of flood risk in your area.
- Sign up for local alerts. Ready.gov advises signing up for your community’s warning system. The Emergency Alert System and NOAA Weather Radio also send emergency alerts.
- Buy flood insurance early. Ready.gov notes that homeowner’s policies typically do not cover flooding, and a flood policy can take up to 30 days to take effect. Buy well before a storm is forecast.
Make a household plan
Ready.gov recommends making a plan that covers everyone in the household, including pets. Practise your evacuation routes and shelter plans, and know where you will go if you are told to leave. Agree on how you will contact each other if phone networks are down.
Prepare a supply kit with non-perishable food, water and cleaning supplies for several days, in case you must leave immediately or services are cut off. Keep important documents in a waterproof container and make password-protected digital copies.
Protect your property
- Move valuables to higher levels of the home.
- Clear drains and gutters so water can run away from the building.
- Install check valves to stop sewer backflow.
- Consider a sump pump with a battery backup in case of power loss.
During a flood: the rules that save lives
Ready.gov’s flood guidance is direct: do not walk, swim or drive through flood water. It adds several specific rules:
- Evacuate immediately if authorities tell you to.
- Never drive around barricades. Responders place them to direct traffic away from flooded areas.
- Stay off bridges over fast-moving water. Ready.gov warns that fast-moving water can wash bridges away without warning.
- If your car is trapped in rushing water, stay inside unless water is rising inside the car. If it is, get onto the roof.
- If trapped in a building, move to the highest level. Do not climb into a closed attic, because you can be trapped there by rising water.
Treat any moving floodwater as dangerous, even when it looks shallow. Ready.gov’s rule is simple: turn around, don’t drown.
Electrical and contamination hazards
Ready.gov warns that underground or downed power lines can electrically charge the water. Do not touch electrical equipment if it is wet or if you are standing in water. If it is safe to do so, turn off the power at the mains. Do not use a generator indoors or near windows; use it only outdoors and away from openings.
Floodwater can be contaminated and contain sharp debris, so avoid wading in it where possible.
After the flood
- Return home only when authorities say it is safe.
- Avoid driving except in emergencies, because roads may be damaged or still flooded.
- Wear heavy work gloves, boots and protective clothing during cleanup.
- Use an appropriate mask if cleaning mould or debris. People with asthma or other lung conditions, or a weakened immune system, should not enter buildings with visible mould or indoor water leaks.
- Keep children out of cleanup work.
- Be aware of the risk of snakes and other animals that may have moved into the house.
Quick checklist
- Know your flood risk and sign up for local alerts.
- Have an evacuation route and a meeting point that everyone knows.
- Keep a supply kit and waterproof copies of key documents.
- Never walk, swim or drive through moving water.
- Stay off bridges over fast-moving water.
Related reading: The recent floods in Nepal and Hurricane Isaias on the US Gulf coast show how quickly water can rise and how long recovery takes. If a flood cuts power in your home or business, the guide to securing connected cold storage explains how to keep food safe in a freezer that may have warmed up.
Frequently asked questions
How quickly can a flash flood happen?
A flash flood can develop within minutes or a few hours of heavy rain or a dam failure, which is why alerts and an early decision to leave matter so much.
Is a car safe in floodwater?
No. Do not drive through flood water. If your car is trapped in rushing water, Ready.gov advises staying inside unless water is rising inside the car, in which case you should get onto the roof.
Does home insurance cover flood damage?
Ready.gov notes that homeowner’s policies do not cover flooding. A separate flood policy, such as one under the National Flood Insurance Program, is needed, and it can take up to 30 days to start.
What should I do if water enters my home?
Move to the highest level if you are trapped, avoid electrical equipment in or near water, and signal for help if you are on a roof. Do not enter the water to reach the house.
Is it safe to return home after a flood?
Only when authorities say it is safe. Check for structural damage, electrical hazards and contamination before going in.
Sources
- Ready.gov: Floods
- National Weather Service: Flood Safety Tips and Resources
- Ready.gov: Make a Plan
- Ready.gov: Evacuation
- National Weather Service: Home
