FLOOD05175

• County: Summit
• Community: Breckenridge
• Stream Name: Blue River
• Basin: Colorado Mainstem
• Title: Technical Addendum Floodplain Information Blue River
• Date: 12/1/1974
• Prepared For: Summit County
• Prepared By: Leonard Rice Consulting Water Engineers, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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II. Location and areal distribution of precipitation for the
lOO-year event
A. Location

}~teorological studies have shown us that in
moUntainous areas elevated regions are favored for
the origination of oonvection. Also, such studies
have shown that regions of low level ro nvergence a.re
also favored regions. These two factors can both be
combined in a region along the Continental Divide in
the southern end of the mue River Basin. Three ele-
vated regions in the southern basin end exist: the
Red }buntain-Silverheels .l-buntain complex, the Eald
-Ynuntain-fureas }buntain complex, and the Glacier
~buntain-Red Cone complex. The low level convergence
zone formed by flow up the NW-SE mue River Valley
and flow up the South Park region (channeled by the
Sangre de Cristo Range) exists along the Continro1tal
Divide. Two of the three elevated regions are sub-
ject to the full force of the convergence zone; the
Red Ht.-Silverheels Nt. complex, and the Bald Nt.-
Boreas Nt. complex.
It is therefore most likely that over these
complexes the convective activity will be concentra-
ted. One can visualize that the incident solar ra-
diation on the elevated areas vlill act as a trigser
to set off ronvection and thereby organize the meso-
scale flow. Such a process, once initiated, can con-
tinue a considerable length of time. ~1e approximate
location of the convective centers can be determined
by approximating the elevated a.rea centers with
respect to the mean flow and general convergence pat-
tern.

B. Areal distribution

The areal di stri bution of rain from cumulous
clouds has been shown to be somewhat larger than the
updraft for a plains type system. This is what one
would expect from potential flow solutions of a jet
impacting against a flat plate. In the mountains,
the solution is not as simple. Complex mountai. n top-
ography makes a general solution extremely difficult,
solvable only for a given region. In this study, I
will assume for a first approximation that the areal
distribution is the same as the updraft, realizing
that this is a conservative estimate.
The approach I used was to estimate from pub-
lished values the critical updraft area necessary to
process enough air, at a given efficiency, to produce
a volume of water observed over a variable size