FLOOD04316

• Designation Number: 507
• County: Arapahoe
• Community: Aurora
• Basin: South Platte
• Title: Flood Insurance Study - Aurora, Adams, Douglas and Arapahoe Counties
• Date: 9/1/1998
• Designation Date: 11/1/1999
• Floodplain - Doc Type: Floodplain Report/Masterplan

3.2 Hydraulic Analyses

Analyses of the hydraulic characteristics of flooding from the
sources studied were carried out to provide estimates of the
elevations of floods of the selected recurrence intervals.

Cross section data for Sand Creek were taken from topographic
maps at a scale of 1:1200 (Reduced to 1:6,000), with a contour
interval of 2 feet (Reference 20). Toll Gate Creek cross
sections were taken from 1:1,200 scale (reduced to 1:2,400),
2-foot contour interval topographic maps, and were
supplemented with field cross sections (References 21 and 22).

The West Toll Gate Creek an~ East Toll Gate Creek cross
section data were taken from topographic maps at a scale of
1:1,200 (reduced to 1:2,400), with a contour interval of 2
feet (Reference 22), and were supplementec! wi th field cros s
sections in areas of new developement. The West Toll Gate
Tributary, Cherry Creek Spillway, and Unnamed Creek cross
section data were obtained by field survey. The cross section
data for Westerly Creek were taken from topographic maps at a
scale of 1:1,200 (reduced to 1:6,000), with a contour interval
of 2 feet (Reference 23), The cross section datl!~ for Sable
Ditch, Sable Ditch Overflow, and Granby Ditch were taken from
topographic maps at a scale of 1:2,400, with a contour
interval of 2 feet (Reference 24). All bridges and culverts
were field surveyed to obtain elevation data and structural
geometry.

Locations of selected cross sections used
analyses are shown on the Flood Profiles
stream segments for which a floodway was
4.2), selected cross section locations are
FIRM (Exhibit 2).

in the hydraulic
(Exhibit 1). For
computed {Section
also shown on the

Roughness coefficients (Manning' s "n") for all streams studied
were estimated by field inspection. Roughness values used for
the channels ranged from .025 to .050 and from .030 to .070
for the overbanks.

Water-surface profiles were developed
Step-Backwater Model (Reference 25).
for the 10-, 50-, 100-, and 500-year
Exhibit 1.

using the HEC-2 Computer
Profiles were determined
floods and are shown in

The approximate studies for Columbia Creek, Side Creek, and
West Toll Gate Creek Tributary between Yale and Hampden were
developed using. normal depth calculations. This analysis
consisted of Obtaining cross section data from U.S. Geological
Survey topograp~ic maps, aerial topographic maps, and using
Manning's equation to develop elevation discharge curves.

The shallow flooding areas were determined using topographic
mapping and field reconnaissance (References 20-24, 26).

20