What causes flash floods and the floods that took place this summer
in Poland?
Flash floods are floods that happen very suddenly and with little
warning.
They are very dangerous. A very heavy rain or an accident like a dam
break can cause one.
Sometimes the ground is too hard or too wet to soak up water. The only
place the rain can go is downstream. Usually rainfall of more than one
inch in one hour is needed to cause a flash flood. Sometimes a place can
get hit by a flash flood even if it's sunny because it might be raining
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 trapped water would rush
down the river at the same time and cause a flash flood.
The floods in Poland this summer weren't flash floods. They were caused
by heavy rainfall but the rain was spread out over days. So much rain
fell that the rivers couldn't handle all the 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 plan ahead.
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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