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.