FLOOD10241

• County: Arapahoe
• Community: Arapahoe County and Incorporated Areas
• Basin: South Platte
• Title: FIS - Arapahoe County and Incorporated Areas - Volume 1
• Date: 8/16/1995
• Prepared For: Arapahoe County
• Prepared By: FEMA
• Floodplain - Doc Type: Current FEMA Regulatory Floodplain Information

Cross section information for channel geometry and surrounding
areas was taken from existing reports (References 40, 41, 42, and
43).

Locations of selected cross sections used in the hydraulic analyses
are shown on the Flood Profiles (Exhibit 1). For stream segments
for which a floodway was computed (Section 4.2), selected cross
section locations are also shown on the Flood Insurance Rate Map
(Exhibit 2).

For the approximate studies,
normal-depth calculations in
taken from USGS maps.

floodplain
approximate,

limits were defined by
typical cross sections

The hydraulic analyses for this study were based on unobstructed
flow. The flood elevations shown on the profiles are thus
considered valid only if hydraulic structures remain unobstructed,
operate properly, and do not fail.

All elevations are referenced to the National Geodetic Vertical
Datum of 1929 (NGVD). Elevation reference marks and the
descriptions of the marks used in this study are shown on the maps.

4.0 FLOODPLAIN MANAGEMENT APPLICATIONS

The NFIP encourages State and local governments to adopt sound
floodplain management programs. Therefore, each Flood Insurance Study
provides 100-year flood elevations and delineations of the 100- and SOO-
year floodplain boundaries and 100-year floodway to assist couununities
in developing floodplain management measures.

4.1 Flood Boundaries

To provide a national standard without regional discrimination, the
1 percent annual chance ODD-year) flood has been adopted by FEMA
as the base flood for floodplain management purposes. The 0.2
percent annual chance (SOD-year) flood is employed to indicate
additional areas of flood risk in the couununity. For each stream
studied by detailed methods, the 100- and SOO-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
1:6,000, 1:1,200, 1:2,400, and 1:24,000, with contour intervals of
2, 10, and 20 feet (References 34 and 44 through S8).

The 100- and SOD-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 (Zones A, AE, and AO), and the SOO-year
floodplain boundary corresponds to the boundary of areas of
moderate flood hazards. In cases where the 100- and SOO-year
floodplain boundaries are close together, only the lOa-year
floodplain boundary has been shown. Small areas within the

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