FLOOD10337 ‎(2)‎

• County: Arapahoe
• Community: Greenwood Village
• Stream Name: Upper Goldsmith Gulch
• Title: Flood Hazard Area Delineation, Upper Goldsmith Gulch
• Date: 4/1/2005
• Prepared For: Urban Drainage and Flood Control District, Arapahoe County and Greenwood Village
• Prepared By: Moser and Associates
• Floodplain - Doc Type: Floodplain Report/Masterplan

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HYDRAULIC ANALYSIS

to convey the 100-year
along Pinewood Avenue and the peak flow

This culvert does not have capacity
delineated

capacity was analyzed using the
flood event. Therefore, the 100,..year
used for the delineation was reduced by the capacity of the box culvert.

HY8 program.
floodplain

were assumed to be completely blocked with

SECTION 3

For purposes of analyzing the foot bridges, the bridge rails
debris and hydraulically ineffective. Moser

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IS

& Associates observed that after a minor storm event nearly

all the bridge rails on the smaller footbridge structures trapped debris up to the high water mark.

the capacity to
J.11~ pipe flow was

were established from guidance in the HEC-RAS model based on the pier shape.
coefficient of 2.6 and contraction

convey the
then reduced from

Expansion

losses at the entrance and

used.

account for hydraulic

was

to

weIr

were used

a

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-

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bridges waterway opening height than 2 feet,
opening would plug during a flood event. Also, the foot bridges just upstream of Orchard Road in Silo
Park are partially plugged with Therefore, these structures were not included
HEC-RAS model.

this small

that

in the

was assumed

it

less

of

sediment.

a

with

foot

For

3.2 ANALYZED FLOOD FREQUENCIES
The flood events used to analyze the hydraulic capacities of the channels
and 500-year flood frequencies.

in this study are the

and structures

100-,

50-,

10-,

10-

The profiles for the
Water surface profiles
the flow was not

WATER SURFACE PROFILE DETERMINATION
surface profiles were calculated for the 10-, 50-, 100-, and 500-year events.
and 100-year events are included on the FHAD drawings in Appendix E.

3.3
Water

were

year
determined using the HEC-RAS program assuming sub-critical flow.
flow regime, the model results reported a critical

in the sub-

Where

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water surface elevation at that cross section.

critical

The FIS

Since the FIS

Bridge pier coefficients
For roadway overtopping analysis,
coefficients of 0.3 and 0.5, respectively,
exist of bridges and culverts.

obtained from the FIS

the project mapping.
culvert hydraulics

was

100-year starting water surface elevation at
water surface elevation was adjusted to be on the same vertical datum as
did not include water surface

Belleview Avenue

The

to

used

were

return periods,
approximate the backwater due to the Belleview Avenue structure.

other

for

elevations

3-2

Immediately downstream of Arapahoe Lake on Goldsmith Gulch lower flows are conveyed through a 8 foot
concrete box culvert located underneath the subdivision and Pinewood A venue. The box culvert

by 4 foot