FLOOD04120

• Designation Number: 378
• County: Boulder
• Community: Louisville
• Stream Name: Local Drainage
• Basin: South Platte
• Title: Floodplain Information Report - Louisville, Colorado
• Date: 8/1/1994
• Designation Date: 9/1/1994
• Floodplain - Doc Type: Floodplain Report/Masterplan

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b, Cooperation with Other Agencies

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All flood hazard studies in Colorado are coordinated through the
Colorado Water Conservation Board, Other flood investigations have
been made in Boulder County; however, this flood insurance study
is the first major report study for the City of Louisville.

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c, Sources of Basic Data

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Basic data were collected and assembled by the Soil Conservation
Service. Engineering field surveys consisted of vertical and hori-
zontal control and cross sections at representative locations. In
addition to the engineering field surveys, hydrologic and hydraulic
data were developed from soils and vegetative cover information,
7 1/2-minute USGS quadrangle maps, a detailed topographic map
(1" = 300'), aerial photographs, and field inspection,

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Data from the Soil Conservation Service report "Flood Insurance Study--
Boulder County Unincorporated Areas" were used for the hydrologic and
hydraulic studies on Coal Creek. This report was prepared in June,
1972 for the Federal Insurance Administration, Department of Housing
and Urban Development,

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d, Water Surface Profiles

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Water surface profiles were developed by standard Soil Conservation
Service channel hydraulics procedures. The computations were based
on surveyed and selected topographic cross sections and peak flows
of 10-year, 2S-year, 100-year, and SOO-year flood frequencies,

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e. Reach Selection

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Five stream reaches were selected because of varied hydrologic,
hydraulic, and flood plain conditions. The reaches were selected on
the basis of channel and flood plain characteristics within each reach,
Of the five reaches, three are on the small separate drainages which
enter Louisville from the west and one is on the Coal Creek flood
plain, The other reach is an overflow area from one of the small
drainages. The reaches are not identified on the report maps, but
are reflected in the zone numbering code (Zone Al refers to the
"A" Zone in Reach 1), Other exhibits specifically identify the reach
illustrated,

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f. Weighted Elevation-Frequency Curves

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Distances above and below the IOO-year base flood in relation to
the frequency of flooding are illustrated on these curves, One
composite elevation-frequency curve was prepared for each reach
using weighted data,

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