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 Miugation Plan . Town of Georgetown. Colorado

Concept 4 - Channel Dredging

The flood carrying capacity of Clear Creek and
South Clear Creek could be increased through
dredging of the channel invert. Implementation of
such an alternative is possible but raises a number
of red flags. First, a 404 Permit would have to be
obtained from the Army Corps of Engineers. This
is an involved process which has been attempted
by the Town in the recent past with limited success.
Dredging would damage many of the habitat values
and aesthetic qualities of the channel, which would
come to more closely resemble a canal than a
natural river. (Even the natural gurgling sound of
the river could be lost). Dredging could also
undermine the stability of the existing revetment
walls of individual landowners which currently line
much of South Clear Creek. Significant costs and
inconvenience to landowners could be incurred in
reconstructing these walls. Finally, long-term
sediment transport conditions in the dredged reaches
would need to be considered. It is expected that
reaches of both streams in Georgetown would
continue to be depositional areas for coarse
sediment transported from the steeper upstream
canyons. A long-term sediment management plan
would have to be developed and adopted. A
preliminary reconnaissance of South Clear Creek
indicated that there was very limited space
downstream of the canyon mouth for a debris basin.

Concept 5 - Permanent Bypass
Conveyance

In flood events of the past 30 years (which have
probably been on the order of 10-year events),
flooding has been confined to South Clear Creek
with the main Clear Creek channel providing

adequate capacity. The initial breakout point for
flows on South Clear Creek has been the reach along
Griffith Street between 8'h and 9th Streets where
the channel bank was purposely breached to reduce
downstream breakouts. Breakout flows were
controlled with sandbags and directed north on
Griffith Street, then west at Park Street and finally
northwest into Clear Creek. Flooding along lower
South Clear Creek could be eliminated by providing
bypass conveyance structures to supplement the
existing channel capacity. The additional
conveyance could conceivably be provided in at
least three different ways;

. Street Conveyance. Streets along the flow path
(Griffith Street, Park Street, etc.) could be
paved and given an inverted crown or curb and
gutter to provide conveyance. This is probably
not practical for a number of reasons:

1) The inverted crown or curb and gutter would
collect treacherous ice for a majority of the
winter.

2) Pavement is difficult and expensive to
maintain in the harsh winter climate of the
mountains and the Town may lack sufficient
tax base to shoulder the added maintenance

costs.

3) Paving and/or curb and gutter would change
the existing rural character of the affected
neighborhood.

. Roadside Ditches. This is probably the least
expensive method of providing bypass capacity
but insufficient room exists on either side of
Griffith Street for a roadside ditch to convey
adequate bypass flows.

((II) MONTGOMERY WATSON . 2-5