FLOOD08859

• County: Clear Creek
• Community: Georgetown
• Basin: South Platte
• Title: Flood Control Master Plan and Local Pre-Disaster Flood Mitigation Plan
• Date: 7/1/1998
• Prepared For: Georgetown
• Prepared By: Clear Creek County Office of Emergency Management
• Floodplain - Doc Type: Flood Mitigation/Flood Warning/Watershed Restoration

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Flood Control Master Plan and Local Pre-Disaster Flood Hazard Mitigation Plan . Town of Georgetown, Colorado

impact of flooding on other residences. It is likely
that flood proofing measures such as building
elevation and floodwall/levee systems could not
be cost effectively used to eliminate the current
danger to all 85 flood-prone structures in
Georgetown. However, such measures might be
selectively used to protect historically significant
structures or those unusually susceptible to flood
damage if other approaches prove infeasible or
fmancially prohibitive.

Concept 2 . Channel Floodwalll
Levee System

The majority of flooding problems originate and
impact areas upstream of 15th Street on Clear Creek.
A levee protection concept is impractical for these
areas because of the proximity of residences and
fences to the creek banks. However, along these
reaches vertical floodwalls could be utilized in place
of a levee. Floodwalls should be vertical extensions
of the existing stone, timber or concrete revetment.
Concrete walls could be given a facade of native
stone or wood to improve aesthetics. Even with a
natural facade, floodwalls would undeniably change
the aesthetic character of the creeks.

An important consideration for floodwalls are
FEMA guidelines for levee certification that requires
3 feet of freeboard during the tOO-year event. That
is, the top of the floodwall must be 3 feet higher
than the 100-year water surface elevation to obtain
FEMA certification and officially remove properties
from the floodplain. Without certification, a home
or business owner would still be required to
maintain flood insurance. Obviously, floodwalls
high enough to receive certification (probably 5-6
feet on average) would obscure residents' view of

the river and drastically change its character. For
these reasons, the use of a floodwall system
upstream of 15th Street would not be given serious
consideration for 100-year protection. However, a
lower level of protection (e.g., 10-year) could be
considered using this approach.

Concept 3 - Upstream Storage

Approximately % of a mile upstream of Georgetown
on South Clear Creek is a Public Service Company
hydropower facility and appurtenant reservoir.
Another mile further upstream are two natural lakes,
Clear Lake and Green Lake. During the flood of
1995, the hydropower facility did not reduce
discharge levels to mitigate flooding in the town
and apparently is under no obligation to do so in
the future. It has been proposed that, through a
cooperative agreement with the power company,
storage capacity in the reservoir could be used to
reduce flood peaks in the town. By extension, the
two lakes further upstream could also be used to
help mitigate flooding. One problem with this
concept is that historically, flooding in Georgetown
has been the result of spring snowmelt. Such events
produce very long runoff hydrographs (on the order
of weeks or months) and involve extremely large
volumes of water. Even if the complete storage
volume of both upstream lakes and the hydropower
reservoir were utilized to contain snowmelt runoff,
it is possible that they would provide only minimal
flood reduction benefits. Nonetheless, these existing
facilities represent available resources in the
watershed, and every effort should be made to
integrate them into the flood mitigation plan to the
maximum extent possible.

((II) MONTGOMERY WATSON . 2-4