What causes flash floods and the floods that took place this summer
Flash floods occur very suddenly with little advance warning and can be
very dangerous. The are usually caused by a sudden downpour or by an
accident like a dam breaking.
Sometimes the ground is too hard or too wet to absorb water. That means
that all the rain must travel downstream. Usually at least one inch of
rain in an hour is needed to cause a flash flood. Sometimes an area can
get hit by a flash flood even if it's sunny and hasn't rained because it
might be pouring rain on higher ground somewhere.
Dams are designed to hold a river's water in reserve for when people may
need it. If a dam were to break, then all the water in the reservoir
would rush down the river at the same time causing a flash flood.
The floods in Poland and central Europe this summer were caused by heavy
rainfall but weren't flash floods. A heavy rain was spread out over days
and the rivers weren't able to handle that much water. If you want to
know more about the flood in Poland, check here.
Sometimes these kinds of floods can be forecast so people can try and
protect themselves or evacuate. One cause of floods can be forecast
months in advance--snow. Melting snow can cause dangerous floods like
what happened this spring in the upper-midwest U.S.
Submitted by Leah (age 26, Washington DC, USA)
(August 22, 1997)
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