FLOOD02784

• Designation Number: 315
• County: Broomfield
• Community: Broomfield
• Basin: South Platte
• Title: Flood Insurance Study - Broomfield, Colorado, Adams, Boulder and Jefferson Counties
• Date: 9/1/1990
• Designation Date: 3/1/1991
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

9.0 RBVISIONS DBSCRIPTION

This section has been added to provide information regarding significant
revisions made since the original Flood Insurance Study (FIS) was
printed. Future revisions may be ,made that do not result in the
republishing of the FIS report. To assure that any user is aware of all
revisions, it is advisable to contact' the community repository of flood
hazard data located at the City Clerk!s Office, Number Six Garden Office
Center, Broomfield, Colorado 80020.

9.1 First Revision

This study was revised on September 28, 1990, to incorporate the
effects of revised hydrologic and hydraulic analyses along Ni ssen
Reservoir Channel. also known l1S Broomfield Basin 3207. These
analyses, performed by Sellards and Grigg,' Inc. (S&G) of Lakewood,
Colorado, model the effects of two detention ponds (identified as
Ponds 6 and 7l, constructed in, 1988 between Ash Street and 10th
Avenue, and channel improvements made to Nissen Reservoir Channel
between Midway Boulevard and Birch Street.

The hydrologic analysis was performed for this revlSlon using the
Urban Drainage and Flood Contro~ District I s (UDFCD' s) Storm Water
Management Model - PC Version (UDSWM2-PC). As a result of the
construction of Detention Ponds 6 and 7, peak discharges for Nissen
Reservoir Channel have decreased.

The revised hydraulic analyses were performed using the Corps of
Bngineers HBC-2 step-backwater computer program. Flood Profiles
were produced from the HEC-2. and,' as a result, changes were made
to the 100- and 500-year floodplains and 100-year floodway as shown
on Flood Insurance Rate Map (FIRM) and Flood Boundary and Floodway
Map Panel 0220. Topographic maps at a scale of 1: 2 ,400 and a
contour interval of 2 feet, prOduced by the UDFCD. and revised by
S&G in November 1988, were used.to produce the new boundaries. At
the request of the City of Broomfield, the 100-year floodway
between Birch Street and 10th Avenue was defined as being
coincident with the 100-year floodplain. This measure was taken in
order to prevent any future development, specifically around Ponds
6 and 7, which would adversely ~ffect the floodplain downstream of
the revised area.

The Summary of
Profiles have
reanalyses.

Di scharges Tabl~,
been revised to

Floodway Data Table. and Flood
reflect the effects of the

This revision also incorporated a Letter of Map Revision (LOMR)
issued for the City of Broomfield on November 17, 1988. The LOMR
revised a portion of the Nissen. Reservoir Channel between Sheridan
Boulevard and Midway Boulevar~, and the Broomfield Reservoir
Tributary, also shown on FIRM Panel 0220. The basis of the LOMR
was a channelization project along both streams. In support of the
LOMR request, a certified engineering report entitled "Highland
Park South Fi ling No. 2 Let t~r of Map Revi s ion, " prepared by

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