Living with Dams

6 / 24

4 | Living with Dams: Extreme Rainfall Events | 2015
Extreme rainfall events can
severely damage dams and or
cause them to fail completely.
There are more than 87,000 dams
in the United States with various
shapes, sizes, age and uses. From
Hoover and Grand Coulee Dams
out West to the small New England
stone and masonry dams, they all
have potential to cause damage
and loss of life. For that reason, it is
imperative that they are properly
designed and maintained.
Modern dams are built to withstand
earthquakes and floods, seepage
and slope instabilities. Many older
dams were not designed to modern
standards and are showing signs of
deterioration.
Many are in need of maintenance,
upgrading and repair. Dam
engineering and hydrological
science have improved over
the past 50 years as has the
understanding of the risk and
liabilities associated with the
storage of water. Much of this
science is intuitive, understandable
and accepted by dam owners.
Some of it is not and is more
mysterious, such as the size of
potential extreme rainfall events
and the resulting flooding that
follows.
Often the combined effect of a
series of storms repeatedly moving
over the same area, dumping heavy
rains over several days, can cause
rainfall totals similar to a single
extreme rainfall. Meteorologists
refer to this as “storm training.”
Why should I care about
extreme rainfall events?
Data taken from the National Weather Service rain gage stations, State record 24-Hour
Precipitation (most recent data from 2006). Higher amounts have unofficially been recorded
in many states. For example, in Pennsylvania in 1942, 34.5 inches were recorded in a 12
hour period. For more information go to:
Dataunder review
Extreme Rainfall Events By State
5 - 10” 10 - 15” 15 - 25” Greater
than 25”
Maximum 24 hour precipitation
per state (inches)