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

The 100-year floodplain boundaries for the following streams were
obtained from a 1979 UDFCD report (Reference 2):

City Park Channel
City Park Channel South Tributary
Gay Reservoir Channel
Gay Reservoir Channel North Tributary
Nissen Reservoir Channel
West Lake Channel
West Lake Channel Tributary

Additional lOa-year floodplain boundaries on the Gay Reservoir
Channel were obtained from individual consultant engineers.

The SOD-year floodplain boundaries for each of these streams were
delineated by the study contractor.

The floodplain boundaries for Big Dry Creek were obtained from the
Flood Insurance Study for Adams County (Reference 7). The
floodplain boundaries for Rock Creek were taken from a 1976 U.S.
Soil Conservation Service report (Reference 8).
The 100- and SOD-year floodplain boundaries are shown on the Flood
Boundary and Floodway Map (Exhibit 2). In cases where the lOa-and
SOO-year floodplain boundaries are close together, only the
lOa-year floodway boundary has been shown. Small areas within the
floodplain boundaries may lie above the flood elevations but cannot
be shown due to limitations of the map scale and/or lack of
detailed topographic data.

For the flooding sources studied by approximate methods, only the
100-year floodplain boundary is shown.

Approximate lOa-year floodplsin boundaries in some portions of the
study are were taken directly from the Flood Insurance Rate Map for
the City of Broomfield (Reference 9) and the Flood Insurance Study
for Jefferson County, Colorado (Reference 10).

The approximate flooding in the vicinity of the sewage disposal
plant was taken from the 1979 UDFCD report (Reference 2).

4.2 Floodways

Encroachment on floodplains, such as structures and fill, reduces
flood-carrying capacity, increases flood heights and velocities,
and increases flood hazards in areas beyond the encroachment. One
aspect of floodplain management involves balancing the economic
gain from floodplain development against the resulting increase in
flood hazard. For purposes of the NFIP, a floodway is used as a
tool to assist local communities in this aspect of floodplain
management. Under this concept, the area of the 100-year
floodplain is divided into a floodway and a floodway fringe. The
floodway is the channel of a stream, plus any adjacent floodplain
areas, that must be kept free of encroachment so that the 100-year

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