FLOOD01589

• County: Clear Creek
• Community: Georgetown
• Stream Name: Clear Creek, South Clear Creek
• Title: Flood Hazard Identification Report
• Date: 2/1/1987
• Prepared For: Georgetown
• Prepared By: CWCB
• Floodplain - Doc Type: Floodplain Report/Masterplan

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HYDROLOGIC AND HYDRAULIC DETERMINATIONS

Flood History

Major flooding has occurred throughout the study reaches of
Georgetown. A flood occurred along Clear Creek at Rose and 10th Streets
on June 9, 1864. A levee was constructed the following day to keep the
stream within its limits (Ref. 7). Another flood occurred following
three days of heavy rainfall ending on July 23, 1965, when water spilled
out of its banks at three locations along South Clear Creek and an area
from Main to Rose and 8th to 11th Streets was inundated (Ref. 7). A
snowmelt flood occurred along Clear and South Clear Creeks in June,
1983. Sandbagging of the creeks took place and Rose Street was cordoned
off for 3 blocks during evening hours as a precaution.

Flood Characteristics

Flooding in Georgetown is primarily caused by either spring
snowmelt or snowmelt in conjunction with rainfall. An exception to the
usual pattern of flooding occurred on July 23,1965 (see above). Heavy
hailstorms occasionally cause drifts of hail that block drainage paths
and create some flooding.

Hydrologic Analysis

Hydrology for Clear Creek and South Clear Creek was obtained
through methods described in "Manual for Estimating Flood Characteristics
of Natural-Flow Streams in Colorado", commonly referred to as Technical
Manual 1 (see Ref. 5). There are no flood control reservoirs upstream
from town on either creek, nor any detention reservoirs.

Hydrology for Clear Creek at the northern corporate limit of
Georgetown (downstream from its confluence with South Clear Creek) was
derived through a statistical analysis of annual peak flows at USGS gage
06716500, Clear Creek near Lawson. This information was then transferred
to the subject location using a procedure detailed in TM-1. The
procedure involved a weighting of the computed flood peaks at the gage
with flood peaks calculated with regional regression equations (Mountain
Region equations). Drainage area ratios are also employed in this
method. Data used in establishing peak flows were as follows: 38 years
of annual peak flows from the Lawson gage data (water years 1946-84,
excluding 1956); drainage area at the gage; drainage area at Georgetown's
northern corporate limit; and mean annual precipitation above the gage.
The statistical analysis of the 38 years of gage data used a Log-Pearson
Type 3 fitting of the data.

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