What causes flash floods and the floods that took place this summer in Poland?

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 (Washington DC, USA)
(August 22, 1997)





Last modified April 28, 2016 by Jennifer Bergman.

You might also be interested in:

What are the retrograde motions of planets in the sky?

It depends on what kind of motion you are talking about. When seen from the north pole of the celestial sphere all planets orbit around the Sun in a counter-clockwise or direct path. Most planets also...more

How do Astronauts Live in Space?

Almost everyone has a question or two about living in space. What do astronauts do in space? How do they do everyday things like eat, sleep and go to the bathroom? Well, this is our attempt to answer...more

How far is the Earth from the Sun, the Moon and all the other planets? How far are all of the planets from the Sun? Do you know of a software that tracks the planets in real-time?

There is a really neat internet program called Solar System Live that shows the position of all of the planets and the Sun for any given day. If you go to that page, you'll see an image similar to the...more

Is it really true that man never really walked on the Moon?

The picture of the American Flag (the one put there by the Apollo astronauts) is waving (or straight out) in the wind. How could that be possible if there is no atmosphere on the Moon? Was it some sort...more

How many planets orbit the sun?

I was wondering if there is a new planet? Are there planets (a tenth planet?) after Pluto belonging to our solar system? What are the names of the new planets discovered in the solar system? Are there...more

According to Stephen Hawking, any object with an energy which equals Plank's energy has to become a black hole.

If that is so, the energy released during the Big Bang must have created many such black holes. Therefore most of the Energy of the Big bang must have disappeared in that form. Then how did the Universe...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA