FLOOD05077

• Designation Number: 351
• County: Arapahoe
• Community: Aurora
• Stream Name: Sable Ditch
• Basin: South Platte
• Title: Letter of Map Revision - Request - Sable Ditch at Sable Boulevard and 23rd Avenue, Aurora, Colorado
• Date: 8/1/1993
• Designation Date: 1/1/1994
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Model (UDSWM2-PC), gave the following discharges for Sable
Ditch at Sable Boulevard:

Existing Land-use
100-vear
Peak flow (cfs) 1007

Future Land
10-year 50-year
610 1065

Use
100-year
1313

Peak discharges from the Flood Insurance study will be used
for the purpose of this report,

III. HYDRAULICS

1. General

The HEC-2 Computer Step - Backwater Model with the
special culvert routine is used to analyze and determine
the water surface profiles for the different flood
frequencies (lOO-year, 50-year and 10-year).

2. Channel and Culverts

Sable Ditch upstream and downstream of the Sable
Boulevard crossing is a trapezoidal concrete lined
channel, having typically a 12 feet wide bottom, 30 feet
wide top width and 1.5 to 1.0 side slopes.

The new cuI verts under Sable Bouleyard are two 9 feet
wide by 6 feet high reinforced concrete box culverts.

Therefore, the first cross-section for the HEC-2 run
should be at least:

(15' - 9') x 4 = 24 feet downstream of the downstream end
of the culverts,

And the upstream cross-section in the channel should be
at least:

(15' - 9') x 1
the culverts,

6 feet upstream of the upstream end of

For the culvert routine, FHWA chart no. 8, scale no. 1
will bE! used since the box culverts have wingwalls
flaring 350 to 600.

3. Cross-sections

A total of eight cross-sections are used for the HEC-2
computer run:

1st cross-section: section 7.0, 30' from downstream end
of culv'~rt.

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