FLOOD07342

• Designation Number: 499
• County: Broomfield
• Community: Broomfield
• Basin: South Platte
• Title: Flood Insurance Study - Broomfield, Adams, Boulder and Jefferson Counties, CO
• Date: 9/1/1997
• Designation Date: 5/1/1999
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

Greiner, Inc., and dated September 1988, was submitted. As a result
of the above-referenced report, the 100-year floodplain boundary
delineations and zone designations were revised. The zone
designation for Nissen Reservoir Channel was redesignated Zone A,
with the lOa-year flood contained in the channel throughout this
reach. The zone designation for the Broomfield Reservoir Tributary
remained Zone A. The Flood Profiles for Nissen Reservoir Channel
have also been revised to reflect the changes due to this LOMR.

9.2 Second Revision

This study was revised on September 30, 1997, to incorporate the
effects of LOMRs dated May 8, 1992, for West Lake Channel and West
Lake Channel North Tributary; January 25, 1994, for Nissen Reservoir
No. 2 spillway and Nissen Reservoir No. 2 Downstream Channel;
August 2, 1995, for City Park Channel; and May 16, 1996, for West
Lake Channel.

In addition, this revision incorporates annexations by the city from
Adams and Weld Counties. The City of Broomfield did not previously
include areas within Weld County.

As part of this revision, the format of the map panels has changed.
Previously, flood-hazard information was shown on both the FIRM and
Flood Boundary and Floodway Map (FBFM). In the new format, all base
flood elevations (BFEs), cross sections, zone designations, and
floodplain and floodway boundary delineations are shown on the FIRM
and the FBFM has been eliminated. Some of the flood insurance zone
designations were changed to reflect the new format. Areas
previously shown as numbered Zone A were changed to Zone AE. Areas
previously shown as Zone B were changed to Zone X (shaded). Areas
previously shown as Zone C were changed to Zone X (unshaded) The
Flood Insurance Zone Data Table was removed from the Flood Insurance
Study report and all zone designations and reach determinations were
removed from the profile panels. In addition, a panel was added to
the FIRM and all FIRM panels were renumbered.

West Lake Channel and West Lake Channel North Tributarv

The May 8, 1992, LOMR was issued to reflect the effects of a
channelization project and detention basin along West Lake Channel
and West Lake Channel North Tributary. The revision affects West
Lake Channel from the detention basin outfall upstream of King
Circle to just upstream of Lowell Boulevard and West Lake Channel
North Tributary from its confluence with West Lake Channel to just
downstream of West 136th Avenue. Because the base flood is
contained within the detention basin and the channelized reaches of
West Lake Channel and West Lake Channel North Tributary, the BFEs
were removed and these areas were designated Zone A.

A new hydraulic analysis was performed by P.R. Fletcher &
Associates, Inc., using the U.s. Army Corps of Engineers (USACE)
HEC-2 computer program (Reference 16) and detention-pond routing was
performed using the USACE HEC-1 computer program (Reference 17).
Cross-section data for the revised analysis were obtained from post-
construction field surveys. Starting water-surface elevations for
West Lake Channel were obtained from the original study and the
starting water-surface elevations for the detent~on pond were
obtained through the use of the HEC-l Level Pool Reservoir Routing
computer model (Reference 17). The results of the analysis are
presented in the report entitled "Request for Letter of Map
Revision, Trails at West Lake, Broomfield, Colorado," prepared by

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