Flash Floods

6th Grade

FLASH FLOODS

Flash Flood: #1 weather-related killer in the United States!

What can cause floods? • Heavy rain

• Snow melt

• Dam breaking

• Ice jams

• Hurricanes

• Tropical Storms

What is the difference between a flash flood and a real flood

• FLASH FLOOD: a life-threatening flood that begins within 6 hours —and often within 3 hours—of the rain event.

• NORMAL FLOOD: is a longer term event and may last a week or more.

Where do they occur?

• Normally associated with a defined body of water, but flash floods can occur in normally dry areas with no visible stream channel

In a flash flood there is rapid inundation of:

• Normally dry areas

• Roads

• Underpasses

• Buildings

What are usually the major causes of Flash Floods?

• Slow-moving thunderstorms repeatedly moving over the same area

• Heavy rains from hurricanes and tropical storms

Hurricane-induced Flood

Hurricane Floyd,1999

Floyd,1999: North Carolina

Katrina, 2005: New Orleans, LA

Hurricane Katrina, 2005

How dangerous can Flash Floods be?

• Flash floods can:– roll boulders– tear out trees– destroy buildings and bridges– scour out new channels.

*Flash floods can reach over 30 feet!

DANGER of FLASH FLOODSClear Fork Road, WV, July 14, 2001 -- This house was torn apart by the flooding of the nearby Clear Fork Creek.

Panther, WV, May 8, 2002 -- Heavy silting happened on many creeks and rivers as a result of the violent flash flood that struck southern West Virginia on May 2, 2002.

Can trigger mudslides

Flooding Types• River Flood: Flooding along rivers is the most common

• Coastal Flood: Winds generated from tropical storms and hurricanes drive ocean water inland and cause significant flooding. Escape routes can be cut off and blocked by Floods can also be produced by sea waves called tsunamis, waves produced by earthquakes or volcanic activity.

• Urban Flood: parking lots and cement is impermeable, losing its ability to absorb rainfall. Urbanization increases runoff 2 to 6 times over what would occur on natural terrain.

• Flash Flooding in Arroyos/Washes: An arroyo is a dry creek bed. Arroyos can fill with fast-moving water very quickly.

• Ice Jam: Floating ice can accumulate at a natural or man-made obstruction and stop the flow of water.

Permeable vs. Impermeable material influences flash floods

Permeability affects Floods

FLASH FLOODING FACTS

• Flooding can occur nationwide

• Flash floods are the #1 weather-related killer in the United States

• Nearly all flash flood fatalities are car-related

• 2 feet of water can float a large vehicle

• 6 inches of water can knock a person down

Watch and Warning

• FLOOD WATCH - means that an overflow of water from a river is possible for your area.

• FLASH FLOOD WATCH - means that flash flooding is possible in or close to the watch area. Flash Flood Watches can be put into effect for as long as 12 hours, while heavy rains move into and across the area.

• FLOOD WARNING - means flooding conditions are actually occurring in the warning area.

• FLASH FLOOD WARNING - means that flash flooding is actually occurring in the warning area. A warning can also be issued as a result of torrential rains, a dam failure or snow thaw.

Flash Flood Safety

• Predicting Floods ---weather satellites, radar, river gauges

• Controlling Floods –dams, sediments, levees

• Flood Safety—moving to higher ground, drivers should not drive on a flooded road, treating water (boiling it) after a flood

What is a levee?

Homework Questions: please answer on a loose leaf sheet of paper

1) What is the #1 weather killer in the US? 2) What are 3 ways that floods can be started? 3) What is the difference between a normal flood

and a flash flood?4) What is a river flood and what causes it? 5) What is a coastal flood, and what causes it? 6) What is an urban flood, and what causes it? 7) What does permeability have to do with flash

floods? 8) What are 3 ways to promote flood safety?