Date: Mon Jun 23 15:35:15 2008 Back to Contents
Author: Paul Nord
Subject: Re: University of Iowa flooding
Isn't that just Poisson statistics?
Two random events are more likely to come in timed close together than
separated by large delays.
Jerry DiMarco wrote:
> Dale, Megan,
> Not to prolong this, but I heard an NPR news story last week
> that sought to explain how an area can have two 500 yr floods so
> close together. According to the expert they had on the program,
> work done to contain a river together with development along its
> shores effectively narrow the river channel. Since the river can no
> longer spread out when it floods, that means the level has to go
> higher. So the old definitions of 100 and 500 year floods, etc. are
> no longer valid. He said we can expect more of these events in the
> future, unless we restore the natural overflow areas that normally
> accompany river systems. Hopefully the powers that be were
> listening or are aware of this, so the money to be spent in the
> aftermath will be allocated wisely...
> P.S. A few years ago the Yellowstone River (~30 miles east of here)
> had two 100 year floods back to back. Same problem, same cause...
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