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Flooding

Floods are among the most frequent and costly natural disasters according to FEMA. As much as 90 percent of the damage related to all natural disasters (excluding drought) is caused by floods and associated debris flows. Floods, on average, kill more than 100 people and are responsible for $4.6 billion in damage in the United States each year.

Most communities in the United States can experience some kind of flooding. Melting snow can combine with rain in the winter and early spring; severe thunderstorms can bring heavy rain in the spring and summer; or tropical cyclones can bring intense rainfall to coastal and inland states in the summer and fall.

As land is converted from fields or woodlands to roads and parking lots, it loses its ability to absorb rainfall. Urbanization increases runoff two to six times more than what would occur on natural terrain. During periods of urban flooding, streets can become swiftly moving rivers, while basements and viaducts can become death traps as they fill with water.

What causes floods and flash floods?
Several factors contribute to flooding. Two key elements are rainfall intensity and duration. Intensity is the rate of rainfall, and duration is how long the rain lasts. Topography, soil
conditions, and ground cover also play important roles.
Flooding occurs in known floodplains when prolonged rainfall over several days, intense rainfall over a short period of time, or an ice or debris jam causes a river or stream to overflow and flood the surrounding area. Floods can be slow- or fast-rising, but generally develop over a period of hours or days.

Most flash flooding is caused by slow-moving thunderstorms, thunderstorms repeatedly moving over the same area, or heavy rains from hurricanes and tropical storms. Flash floods take from several minutes to several hours to develop. Flash floods generally occur within six hours of a rain event, or after a dam or levee failure, or following a sudden release of water held by an ice or debris jam. Flash floods can occur without warning.

Floods can roll boulders, tear out trees, destroy buildings and bridges, and scour new channels. Floodwater can reach heights of 10 to 20 feet (3 to 6 meters) and often carries a deadly cargo of debris. Flood-producing rains can also trigger catastrophic debris slides.

How can I protect myself in a flood?
Regardless of how a flood occurs, the rule for being safe is simple: head for higher ground and stay away from floodwater. Even a shallow depth of fast-moving floodwater produces more
force than most people imagine. It is exceedingly dangerous to try to walk, swim, or drive in floodwater. Two feet (0.6 meters) of water will carry away most vehicles, including sport utility vehicles (SUVs) and pickup trucks. You can protect yourself best by being prepared and having time to act. You can protect your home best by taking measures to reduce potential flood damage (called mitigation) and buying flood insurance in advance.

If you are at risk from floods, you should:
-Find out the elevation above flood stage of your home, outbuildings, and pastures or corrals. Knowing the elevation of your property in relation to nearby streams and dams will let you know if forecasted flood levels will affect your home.
-Find out if local streams or rivers flood easily.
-Talk with members of your household about the possibility of floods and flash floods and what to do to stay safe if one occurs. Knowing how to respond will reduce fear and save precious time in an emergency.
-Find out about the flood evacuation routes in your area and develop a flood evacuation plan for your household. (See "Evacuation, Sheltering and Post-Disaster Safety.") All members of the household should know where to meet each other, where to evacuate to, and what route(s) to take if they have to leave. Making plans well in advance will help you avoid last-minute confusion.
-Find out if you are located in a floodplain, which is considered a Special Flood Hazard Area. If you are, you are still eligible for flood insurance. Check with your city or county government (start with the Building or Planning Department) to review the Flood Insurance Rate Maps, published by the Federal Emergency Management Agency (FEMA). If your home is especially vulnerable, consider relocation.
-Talk to your insurance agent. Homeowners' policies do not cover flooding. Ask about the National Flood Insurance Program (NFIP) (www.fema.gov/nfip).
-Use a NOAA Weather Radio or listen to local stations on a portable, battery powered radio or television for updated emergency information.
-If you live in a frequently flooded area, stockpile emergency building materials. These include plywood, plastic sheeting, lumber, nails, hammer and saw, pry bar, sand, shovels, and sandbags.
-Avoid building in a floodplain unless you elevate and reinforce your home. Some communities do not permit building in known floodplains. If there are no restrictions and you are building in a floodplain, take precautions to make it less likely your home will be damaged during a flood.
-Keep insurance policies, documents, and other valuables in a safe-deposit box. You may need quick, easy access to these documents. Keep them in a safe place less likely to be damaged during a flood.
-Raise your furnace, water heater, and electric panel to higher floors or the attic if they are in areas of your home that may be flooded. Raising this equipment will prevent damage. An undamaged water heater may be your best source of fresh water after a flood.
-Install check valves in plumbing to prevent floodwater from backing up into the drains of your home. As a last resort, when floods threaten, use large corks or stoppers to plug showers, tubs, or basins.
-Construct barriers such as levees, berms, and flood walls to stop floodwater from entering the building. Permission to construct such barriers may be required by local building codes. Check local building codes and ordinances for safety requirements.
-Seal walls in basements with waterproofing compounds to avoid seepage through cracks.
-Consult with a construction professional for further information about these and other damage-reduction measures. Check local building codes and ordinances for safety requirements.
-Contact your local emergency management office for more information on mitigation options to further reduce potential flood damage. Your local emergency management office may be able to provide additional resources and information on ways to reduce potential damage.
-Ensure that any outbuildings, pastures, or corrals are protected in the same way as your home. When installing or changing fence lines, consider placing them in such a way that your animals are able to move to higher ground in the event of flooding.