FLOOD09227

• Designation Number: 530
• County: Adams
• Community: Unincorporated Adams County
• Basin: South Platte
• Title: FIS - Adams County and Incorporated Areas Volume I of III
• Date: 8/1/1995
• Designation Date: 9/1/2000
• Floodplain - Doc Type: Floodplain Report/Masterplan

4.1 Floodplain Boundaries

To provide a national standard without regional discrimination, the
l percent annual chance (lOO-year) flood has been adopted by FEMA
as the base flood for floodplain management purposes. The 0.2
percent annual chance (500-year) flood is employed to indicate
additional areas of flood risk in the community. For each stream
studied by detailed methods, the lOO- and 500-year floodplain
boundaries have been delineated using the flood elevations
determined at each cross section. Between cross sections, the
boundaries were interpolated using topographic maps at scales of
l:24,000, l:2,400, l:6,000, and l:l,200, with contour intervals of
lO and 2 feet (References 34, 35, 40, 42, 43, 45, 47, and 48).

The lOO- and 500-year floodplain boundaries are shown on the Flood
Insurance Rate Map (Exhibit 2). On this map, the 100-year
floodplain boundary corresponds to the boundary of the areas of
special flood hazards (Zone(s) A, AE, AH, and AO); and the 500-year
floodplain boundary corresponds to the boundary of areas of
moderate flood hazards. In cases where the lOO- and 500-year
floodplain boundaries are close together. only the lOO-year
floodplain 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.

Within the City of Commerce City, areas of
outside the aerial photomapping limits were
topographic map at a scale of l:24,OOO, with a
lO feet (Reference 34).

shallow sheet flow
delineated using a
contour interval of

Approximate lOO-year floodplain boundaries within the City of
Federal Heights were delineated using topographic maps at a scale
of l:l,200, with a contour interval of 2 feet (Reference 49).

For the streams studied
floodplain boundary's
(Exhibit 2).

by approximate methods, only the lOO-year
shown on the Flood Insurance Rate Map

Approximate 100-year floodplain boundaries in some portions of the
study area were taken directly from the Flood Hazard Boundary Map
for the City of Thornton (Reference SO).

Approximate
Northglenn
(Reference
(Reference

flood boundaries in some
were taken from the FIA' s
51); others were taken from
52).

portions of the City of
Flood Hazard Boundary Map
USGS Flood Prone Area Maps

For streams studied by approximate methods in other areas of Adams
County, the boundaries of the lOO-year flood were delineated using
the determined elevations and topographic maps (Reference 34), and
were reconciled with USGS Flood Prone Area Maps (Reference 52), and
concurrent studies being done on Second and Third Creeks for the

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