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Go here to find historical and real-time water data for classroom use. For data from a specific river or stream, the interactive National Water Information System Mapper is a good starting point.
What is a 100-year flood and why don't these floods happen every 100 years? This simple fact sheet describes the statistics behind the designation and explains why regular measurements are essential for understanding them.
The term "100-year flood" is part of the national lexicon, but is often a source of confusion. Download and/or print this free poster that attempts to explain the concept, probabilistic nature, and inherent uncertainties of the "100-year flood" to the layman. Print full-size at 44" x 38" or on 11" x 17" paper.