About Floods
What are floods and flashfloods?
The
distinction between a flood and "flash-flood" is usually determined
by the amount of warning (less than six hours for a flash-flood)
that affected areas might receive prior to the flood conditions.
Flash floods may trigger hazardous events
such as mud and landslides, structural bridge failures, and
other threatening conditions. Rainfall intensity and duration
are the primary source of flash floods. Intensity is the rate
of rainfall, and duration is how long the rain lasts. Other
factors include topography, soil conditions, and ground cover.
Floods
are a long-term event and may last several days, or even weeks.
Hurricanes and earthquakes directly cause flood conditions such
as "storm surge" or tsunami respectively. There are also floods
that have characteristics associated with the geographic areas
they are in, such as river, coastal and urban flooding.
River
Floods in Hawaii are usually triggered by hurricane
or tropical storm rains.
Coastal Floods are caused by winds generated
from tropical storms and hurricanes or intense offshore low
pressure systems that can drive ocean water inland and cause
significant flooding.
Urban Floods are triggered because the
paved streets cannot absorb the rainfall. Therefore, the streets
becomes a rivers and people can lose a lot of their property
and some times their lives.
What is the difference between
“watch,” “warning,” and “advisory?”
The
National Weather Services uses specific words when they issue
alerts to the public about dangerous flood-related conditions.
Flash
flood watch: A flash flood is possible in the area,
stay alert.
Flash
flood warning: A flash flood is imminent or occurring;
take immediate action.
Urban and small stream advisory: Flooding
of small streams, streets, urban storm drains, and low lying
areas.