Flood Prevention

Floods are one of the most frequent and costly of natural disasters in terms of hardship and economic losses. Up to 90 percent of the damage related to all natural disasters, (excluding droughts) is caused by floods and associated debris flows. Most communities in the United States can experience some kind of flooding. Between 1988 and 1997 floods cost the nation approximately $3.7 billion annually. The long- term annual average of lives lost in floods from 1940 to 1999 was 110 per year.

Causes of Floods

Flooding occurs in known floodplains due to, (1) prolonged rainfall lasting several days, (2) intense rainfall over a short period of time, or (3) an ice or debris jam that causes a river or stream to overflow and flood the surrounding area. Other contributors to flooding are snow- melt that combine with rain in the winter and early spring; severe thunderstorms; and tropical cyclones that bring intense rainfall to the coastal and inland states in the summer and fall.

Flash floods occur within six hours of, (1) a rain event, (2) after failure of a dam or levee, or (3) following a sudden release of water held by an ice or debris jam. Because there is not always time for advance warning, flash floods can catch people by surprise and allow little if any time to prepare for their damage. Most flash flooding is caused by slow-moving thunderstorms, thunderstorms repeatedly moving over the same area, or heavy rains from hurricanes and tropical storms. Floods, on the other hand, can develop over a period of hours or a period of days.

Two key elements that contribute to flooding 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 rolls. Natural areas, areas undisturbed by humans, have plants growing in the soil that are able to absorb excess rain. As land is converted from fields and woodlands to roads and parking lots, it loses its ability to absorb rainfall. Urbanization increases runoff two to six times what would occur on natural terrain. During periods of urban flooding streets can become swift moving rivers and basements and viaducts can become death traps as they fill with water.

National Weather Service Watches and Warnings

A National Weather Service WATCH is a message indicating that conditions favor the occurrence of a certain type of hazardous weather. When a severe thunderstorm watch is issued it means that a severe thunderstorm is expected in approximately six hours within an area approximately 120 to 150 miles wide and 300 to 400 miles long (36,000 to 60,000 square miles). Flash flood watches are issued 12 to 36 hours in advance of a possible hazardous flooding event.

A National Weather Service WARNING is a message stating that a hazardous event is occurring or is going to occur in 30 minutes to an hour. These warnings are issued on a county-by-county basis.

What To Do During A Flood Watch

¨ Listen to a NOAA weather radio or a portable battery operated radio for updated storm or flood information

¨ Be ready to respond and act quickly

1. Fill bathtubs, sinks, and plastic bottles with clean water as water may become contaminated or service interrupted under flood conditions.

2. Bring outdoor belongings as patio furniture or gas grills indoor so they will not be swept away or damaged by floodwaters.

3. Move your furniture and valuable to higher floors of your home where they are less likely to receive damage in a flood.

4. If instructed by local authorities, turn off all utilities at the main power switch and close the main gas valve.

5. Get your evacuation supply kit ready.

6. Fill your car’s gas tank, in case an evacuation notice is issued.

What To Do If A Flood Warning Is Issued

¨ Listen to a NOAA Weather Radio, or a portable battery-powered radio (or television) for updated emergency information.

¨ Be alert of signs or flooding.

¨ If you live in a flood-prone area or think you are at risk, evacuate immediately. Move quickly to higher ground. It is more important to save yourself than your belongings. Be sure to lock house doors and windows before you leave.

¨ Follow the instructions and advice of local authorities a s the county emergency manager or sheriff’s office.

¨ If advised to evacuate, do so immediately. It is important to move to a safe area before access is cut off by floodwaters. Evacuation is much simpler and safer before floodwaters become too deep for vehicles to drive through.

¨ Follow recommended evacuation routes. Shortcuts or alternate non-recommended routes may be blocked or damaged by floodwaters.

¨ Leave early enough to avoid being marooned by flooded roads.

Flood Safety

¨ Stay out of areas subject to flooding. Dips, low spots, canyons, washes, etc. can become filled with water.

¨ If outdoors, climb to high ground and stay there. Move away from dangerous floodwater.

¨ If you come upon a flowing stream where water is above your ankles, turn around and go another way. Never try to walk, swim, or drive through such swift water. Most flood fatalities are caused by people attempting to drive through water, or people playing in high water. If it is moving swiftly, even water six inches deep can sweep you off your feet.

What To Do If Driving Your Car During a Flood

¨ Avoid already flooded areas, and areas subject to sudden flooding. Do not attempt to cross-flowing streams. Most flood fatalities are caused by people attempting to drive through water, or people playing in high water. The depth of water is not always obvious. The roadbed may be washed out under the water, and you could be stranded or trapped. Rapidly rising water may stall the engine, engulf the vehicle and its occupants, and sweep them away. Look out for flooding at highway dips, bridges, and low areas. Two feet of water will carry away most automobiles.

¨ If you are driving and come upon rapidly rising water, turn around and find another route. Move to higher ground away from rivers, streams, creeks, and storm drains. If floodwaters or barricades block the route, find another route.

¨ If your vehicle becomes surrounded by water or the engine stalls, and if you can safely get out, abandon your vehicle immediately and climb to higher ground. Many deaths have resulted from attempts to move stalled vehicles. When a vehicle stalls in the water, the water’s momentum is transferred to the car. The lateral force of a foot of water moving at 10 miles per hour is about 500 pounds on the average automobile. The greatest effect is buoyancy-for every foot that water rises up the side of a car, it displaces 1,500 pounds of the car’s weight. So, two feet of water moving at 10 miles per hour will float virtually any car. Many persons have been swept away by floodwater upon leaving their vehicles, which are later found without much damage. Use caution when abandoning your vehicle, and look for an opportunity to move away quickly and safely to higher ground.

What To Do After the Flood

¨ Do not use fresh food that has come into contact with floodwaters

¨ Drink only water that has not been contaminated

¨ Do not visit the disaster area. Your presence will only hamper rescue and other emergency operations

¨ Do not handle electrical equipment in wet areas. Electrical equipment should be checked and dried before use.

¨ Use battery-powered lanterns or flashlights, not oil or gas lantern or torches to examine buildings. Flammable materials may be present.

¨ Report broken utility lines to the utility company or 911-dispatch center.

¨ Keep tuned to your radio or television station for advice and instructions from local government on where to obtain medical care, where to get assistance for such necessities as housing, clothing, and food.