FLOOD05175

• County: Summit
• Community: Breckenridge
• Stream Name: Blue River
• Basin: Colorado Mainstem
• Title: Technical Addendum Floodplain Information Blue River
• Date: 12/1/1974
• Prepared For: Summit County
• Prepared By: Leonard Rice Consulting Water Engineers, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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BASIN CHARACTERISTICS

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To synthetically derive flood flows of the Blue River required
determination of the physical characteristics of the basin such
as type and extent of cover, soil, infiltration rates, Mannings
"n" values and other related parameters. This data was collected
through map interpretation and field inspections. Mapping for
the upper basin areas or the areas above the town of Breckenridge
were based on U.S.G.S. 7~ minute quadrangle maps. Through the
town of Breckenridge, mapping at 2 ft. contour intervals and a
scale of 1:100 was provided for flood plain determination.

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The SCS method of estimating infiltration was utilized in the study.
Soils in the basin were grouped into hydrologic classifications
with the aid of detailed soils maps from the Kremmling SCS office
and the General Soils Map for Summit County, also done by the
SCS. The entire basin upstream of Breckenridge was classified as
hydrologic Group A. The east side of the Blue basin below
Breckenridge was classified as Group B and the west side was
grouped in the C category.

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Forest cover was measured using the U.S.G.S. 7~ minute quads of
the area. Appropriate values for the soil cover complexes were
selected using Appendix A of the Desiqn of Small Dams. Composite
I runoff curve numbers were derived for each tributary.

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Soil moisture condition II was selected to duplicate average
conditions existing in the basin at the time of the storm. Soil
moisture condition III was not used to derive curve numbers be-
cause it was felt that saturated soil conditions prior to rainfall
would result in a runoff event that would produce a flood greater
than what would occur under average conditions. Soil curve numbers
averaged75.5 and varied from 60 to 87, depending on the relative
location within the basin:. ---

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Drainage areas for the major tributaries to the Blue River in the
Breckenridge area are shown in Table 2 that follows.
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~ Leonard Rice Consulting Water Engineers, Inc.