FLOOD09509

• Designation Number: 330
• County: Mesa
• Community: Unincorporated Mesa County
• Basin: Colorado Mainstem
• Title: Flood Insurance Study - Mesa County, Colorado, Unincorporated Areas
• Date: 7/1/1992
• Designation Date: 9/1/1992
• Floodplain - Doc Type: Floodplain Report/Masterplan

development or reV1S1on of existing development in these areas must
be approved by the County Commission, and such new or revised
development is subject to provisions designed to prohibit:

1.

Storage of
detrimental

materials that
to human, animal,

are floatable
or plant life

or

may

be

2. Disposal of garbage or other solid waste

3. Residential use

,~

4.

Creation or deposition of additional debris

5.

Placement of fill, installation of structures, or storage
of materials that could adversely affect floodflow and
possibly cause additional flooding

,

3.0

ENGINEERING METHODS

.

For the flooding sources studied by detailed methods 1n the community,
standard hydrologic and hydraulic study methods were used to determine
the flood hazard data required for this study. Flood events of a
magnitude which are expected to be equaled or exceeded once on the
average during any 10-, 50-, 100-, or 500-year period (recurrence
interval) have been selected as having special significance for
floodplain management and for flood insurance rates. These event s,
commonly termed the 10-, 50-, 100-, and 500-year floods, have a 10, 2, 1
and 0.2 percent chance, respectively, of being equaled or exceeded
during any year. Al though the recurrence interval represents the long-
term, average period between floods of a specific magnitude, rare floods
could occur at short intervals or even within the same year. The risk of
experiencing a rare flood increases when periods greater than 1 year are
considered. For example, the risk of having a flood which equals or
exceeds the 100-year flood (l percent chance of annual exceedence) in
any 50-year period is approximately 40 percent (4 in 10); for any
90-year period, the risk increases to approximately 60 percent (6 in
10). The analyses reported herein reflect flooding potentials based on
conditions existing in the community at the time of completion of this
study. Maps and flood elevations will be amended periodically to
reflect future changes.

3.1

Hydrologic Analyses

.

Hydrologic analyses were carried out to establish peak discharge-
frequency relationships for each flooding source studied by
detailed methods affecting the community.

In 1985, the COE performed a hydrologic study of the Colorado River
for Glenwood Springs to DeBeque Canyon (Reference 10).

A hydrology
prepared by
this study,
yea r fl ood s

report on the Colorado River dated May
J. F. Sato and Associates, Inc. (Reference
the peak discharges for the 10-, 50-, 100-,
on the Colorado River from DeBeque Canyon to

1989,
11) .
and
the

was
In
500-
Utah

17