FLOOD00643

• County: Boulder
• Community: Boulder County
• Stream Name: Boulder Creek
• Title: Flood Hazard Area Delineation - Boulder Creek
• Date: 1/1/1983
• Prepared For: Boulder County
• Prepared By: UDFCD
• Floodplain - Doc Type: Floodplain Report/Masterplan

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- AUTHORIZATION -

This study was prepared under the current format of the District's Flood Hazard
Area Delineation Reports. The study scope consists of an analysis of the
100-year flood event extending westward from the Valley View Road crossing to
just downstream of the Arapahoe Avenue crossing at the mouth of Boulder Canyon.
Although not included in the report, water surface profiles for the 10-, 50- and
500-year floods were determined as part of the study contract for use by FEMA
and the City of Boulder. The delineation of the 500-year floodplain was also
prepared on a drawing separate from this report.

BOULDER CREEK FLOOD HAZARD AREA DELINEATION

This report was authorized and contracted through the Urban Drainage and Flood
Control District as part of a program of identifying floodprone areas within
the District's jurisdiction.

This study identifies floodprone areas along Boulder Creek within the City of
Boulder, Colorado. The floodplain information included in this report is
provided to the local government to enable the enactment of a comprehensive
local floodplain management program.

Included in this report are Flood Hazard Area Maps which show the areas that
would be inundated by the 100-year flood event. The water surface profile shows
the 100-year flood elevations along the channel related to Mean Sea Level (MSL)
Datum, also referred to as National Geodetic Vertical Datum (NGVD).

Upon acceptance of this report by the Urban Drainage and Flood Control District
,
and the designation and approval of the flood hazard areas by the Colorado Water
Conservation Board, this study can be used by the City of Boulder to regulate
future floodplain construction, to guide future drainageway improvements and to
plan flood protection measures along the channel and floodplain of Boulder Creek.

Three floodways were also computed as part of this study based upon three sets
of criteria specified by the District and the City of Boulder. Special review
meetings were held with the City and the District to present the alternative
floodways and initiate the floodway selection process. Floodway data for the
selected regulatory floodway will be prepared as an addendum to this report at
a later date.

- PURPOSE, SCOPE AND STUDY PROCESS -

The purpose of the floodway is to designate those areas to be kept free from
future encroachment and reserve an area for conveyance of the 100-year flood
along Boulder Creek. Floodway criteria is designed to limit future increases
in flood stage and velocity resulting from floodplain development.

This report was prepared to guide local officials in planning the use and regula-
tion of the 100-year floodplain. The report includes information on past floods
and the nature and extent of probable future floods along a 4.8 mile study reach
of Boulder Creek. This report, along with other information prepared as part of
the study contract, will be used by the Federal Emergency Management Agency (FEMA)
in the preparation of a revised Flood Insurance Study and Flood Insurance Rate
Map for the City of Boulder.

The flood profile and floodplain delineation presented in this report are based
on existing floodplain and channel conditions, with special consideration for
potential debris blockage at major stream crossings. Flood elevations and the
corresponding floodplain are often altered by road and bridge construction,
floodplain development, flood control improvements, or natural processes. Prior
to utilization of this report for planning or design purposes, the user is

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