Types of Flooding
- River Flooding
Flooding along rivers is a natural and inevitable part of life. Some floods occur seasonally when winter or spring rains, coupled with melting snoww, fill river basins with too much water too quickly. Torrential rains from decaying hurricanes or tropical systems can also produce river flooding.
- Coastal Flooding
Winds generated from tropical storms and hurricanes or intense offshore low pressure systems can drive ocean water inland and cause significant flooding. Escape routes can be blocked off and blocked by high water. Coastal flooding can also be produced by sea waves called tsunamis, sometimes referred to as tidal waves. These waves are produced by earthquakes or volcanic activity.
- Urban Flooding
As land is converted from fields or woodlands to roads or parking lots, it loses its ability to absorb rainfall. Urbanization increases runoff 2 to 6 times over what would occur on natural terrain. During periods of urban flooding, streets can become swift moving rivers, while basements can become death traps as they fill with water.
- Flash Flooding
Several factors contribute to flash flooding. The 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 an important role.
Flash floods occur within a few minutes or hours of excessive rainfall, a dam or levee failure, or a sudden release of water held by an ice jam. Flash floods can roll boulders, tear out trees, destroy buildings and bridges, and scour out new channels. Rapidly rising water can reach heights of 30 feet or more. Furthermore, flash flood-producing rains can also trigger catastrophic mud slides. You will not always have a warning that these deadly, sudden floods are coming. Most flood deaths are due to FLASH FLOODS.
Most flash flooding is caused by slow-moving thunderstorms, thunderstorms repeatedly moving over the same area, or heavy rains from hurricanes and tropical storms.
Impacts to Automobiles
Nearly half of all flash flood fatalities are auto related!!!
Never drive your automobile into moving water, especially if you cannot tell how deep the water is.
Water weighs 62.4 lbs. per cubic foot and typically flows downstream at 6 to 12 miles per hour.
When a vehicle stalls in the water, the water's momentum is transferred to the car. For each foot the water rises, 500 lbs. of lateral force is applied to the automobile.
But the biggest factor is bouyancy. For each foot the water rises up the side of the car, the car displaces 1500 lbs. of water. In effect, the automobile weighs 1500 lbs. less for each foot the water rises.
Two feet of water will carry away most automobiles!!!
Watches, Warnings, and Advisories
- Flash Flood or Flood Watch: Flash flooding or flooding is possible within the designated WATCH area - be alert!
- Flash Flood or Flood Warning: Flash flooding or flooding has been reported or is imminent - take necessary precautions at once!
- Urban and Small Stream Advisory: Flooding of small streams, streets, and low-lying areas, such as railroad underpasses and urban storm drains, is occurring.
Before the Flood
What YOU can do:
- Know your flood risk and elevation above flood stage.
Do your local streams or rivers flood easily? If so, be prepared to move to a place of safety. Know your evacuation routes.
- Keep your automobile fueled; if electric power is cut off, gas stations may not be able to operate pumps for several days.
- Store drinking water in clean bathtubs and in various containers. Water service may be interrupted.
- Keep a stock of food that requires little cooking and no refrigeration; electric power may be interrupted.
- Keep first aid supplies on hand.
- Keep a NOAA Weather Radio, a battery-powered portable radio, emergency cooking equipment, and flashlights in working order.
- Install check valves in building sewer traps to prevent flood water from backing up into the drains of your home.
- Assemble a disaster supplies kit containing: first aid kit, canned food and can opener, bottled water, rubber boots, rubber gloves, NOAA Weather Radio, battery-powered radio, flashlight, and extra batteries.
What YOUR community can do:
- Assist hospitals and other operations which are critically affected by power failure by arranging for auxiliary power supplies.
- River/rainfall readings are valuable to local emergency management agencies (EMA) and the National Weather Service (NWS) in assessing flood conditions and taking appropriate actions. Advanced warning provided by early detection is critical to saving lives. Automatic flood detection systems are available commercially for flood-prone communities. Contact your local NWS office or emergency management agency for further information on LOCAL FLOOD WARNING SYSTEMS.
During the Flood
- Get out of areas subject to flooding. This includes dips. low spots, canyons, washes, etc.
- Avoid already flooded and high velocity flow areas. Do not attempt to cross flowing streams. If you come upon a flowing stream where water is above your ankles, STOP! Turn around and go another way.
- If driving, be aware that the road bed may not be intact under flood waters. Turn around and go another way. NEVER drive through flooded roadways!
- If the vehicle stalls, leave it immediately and seek higher ground. Rapidly rising water may engulf the vehicle and its occupants and sweep them away. Remember, its better to be wet than dead!
- Be especially cautious at night when it is harder to recognize flood dangers.
- Do not camp or park your vehicle along streams and washes, particularly during dangerous conditions.
- Children should NEVER play around high water, storm drains, viaducts, or arroyos.
After the Flood
- If fresh food has come in contact with flood waters, throw it out.
- Boil drinking water before using. Wells should be pumped out and the water tested for purity before drinking. If in doubt, call your local public health authority.
- Seek necessary medical care at the nearest hospital. Food, clothing, shelter, and first aid are available from the Red Cross.
- Do not visit disaster areas. Your presence might hamper rescue and other emergency operations.
- Electrical equipment should be checked and dried before being returned to service.
- Use flashlights, not lanterns, torches or matches, to examine buildings. Flammables may be inside.
- Report broken utility lines to appropriate authorities.
Flood Safety Links