FLOOD01555

• County: Jefferson
• Community: Jefferson County Unincorporated
• Title: Flood Insurance Study - Jefferson County Unincorporated Areas, Volume 1 of 6
• Date: 7/4/1989
• Prepared For: Jefferson County
• Prepared By: FEMA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

9.0 REVISIONS DESCRIPTION

9.1 First Revision

This study was revised on July 4, 1989, to incorporate the effects
of revised hydrologic and hydraulic analyses on the base (lOa-year)
flood elevat ions (BFEs) and floodplain boundaries for port ions of
Bear Creek and North Turkey Creek, in the unincorporated areas of
Jefferson County, Colorado.

The report, entitled "Alternate Hydrologic Analysis for the Flood
Insurance Study for the Unincorporated Areas of Jefferson County,
Colorado," prepared by Messrs D.M. Thomas and John F. Miller, for
FEMA, was utilized as the basis for the revised hydrologic analysis
on Bear Creek and North Turkey Creek. The revised hydraulic
analyses, completed in March 1988, were performed by Michael Baker,
Jr., Inc., as the Technical Evaluation Contractor for FEMA.

The extent of the revi sed detailed study for Bear Creek and North
Turkey Creek is as follows:

1. Approximately 8.4 miles of Bear Creek, including the reach at
Id1edale, the reach from Kittredge to Evergreen, and the reach
upstream of Evergreen Lake. These detailed study reaches are
separated by reaches of approximate study and are therefore
noncontinuous.

2. Approximately 6.9 miles of North Turkey Creek, from Danks
Drive to the upstream limit of detailed study.

The above-referenced report by Messrs Thomas and Miller recommends
mathematical relations for estimating the magnitude and frequency
of flood flows on streams draining more than 15 square miles in
Jefferson County, Colorado. A least square, linear multiple
regression analysis defined the recommended relations from data on
the floodflow, physical, and climatic characteristics observed at
27 sample sites in the South Platte River basin in Colorado.

Basic data for the 27 sites were taken from U.S. Geological Survey
(USGS) reports. The regression analysis utilized "composite curve"
values which were determined by statistically combining individual
flood frequency curves of snowmelt and rainfall floods. The
regression equations utilize three independent basin parameters;
total drainage area, normal annual precipitation, and mean drainage
basin elevation. The equations developed in this study may be used
to estimate flood peak magnitude and frequency at ungaged sites in
Jefferson County with consideration given to their capabilities and
limi tations.

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