FLOOD10411

• County: Denver
• Community: Cherry Creek
• Stream Name: Cherry Creek
• Title: Article - A Flood of Alternatives
• Date: 3/13/1999
• Prepared For: Public
• Prepared By: The Denver Post
• Floodplain - Doc Type: Correspondence

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MRR-16-1999 11:21

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GREENWOOD VILLAGE

Letters to the Editor
1560 Broadway
Denver, CO 80202

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'C" \,-",OJ March IS, 1999

In response to your March 13th editorial "A Flood of Alternatives," you seem to
accept the National Weather Service's in-house review, which was not an
independent revieW, as gospel. Since you apparently have not had the time to do
more research, here are some challenges to the NWS's data and procedures from
Dr. Ed Tomlinson. meteorologist from Monument, Colorado:

1. The terms "Probable Maximum Flood-I> which in turn is based on
"Probable Maximum Precipitation," are misleading terminology because both are
based on extremely improbable events with respect to thl~ Cherry Creek basin.

2. The Army Corps has assumed the Cherry Creek: Dam will fail following a
extraordinary improbable chain of events.

3. The probable maximum precipitation (PMP) is an event that has
somewhere between a one in a million and a one in a billion chance of occurring i
any single year. Unfortunately, the Army Corps will no longer quote probabilities
(ask them) because they have 'endured "bad press" when using these probabilities.
Their new bureaucratic position is that they now no longl:r have to estimate any
probabilities whatsoever! How convenient.

4. The site specific (pMP) study completed by the National Weather Servi.ce
has improperly applied meteorological procedures from publication illv1R52 to th
Cherry Creek basin. even though HMR55A specifically cautions against the use 0
these in the Cherry Creek basin.

5. This error is further compounded by the assumption that the topographic
effects orthe Palmer Divide will increase rainfall in the Cherry Creek basin, which
is contrary to the basic meteorological principle that the Palmer Divide actually
decreas~~ precipitation north of the Palmer Divide into thl:l Cherry Creek basin.

6. The probable maximum flood used by the Army Corps is substantially
greater than the flood estimates prepared by other dam safety officials in the
western U.S.; such PMP estimates are typically 3 times the 100 year rain fall,
whereas the Corps' estimate is 7 times the 100 year rainfall event.

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