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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HYDROLOGIC ANALYSIS

SECTION 2

most

Belleview, the

1989 study at

matched the peak flow from the

recreate a model that

to

important
downstream

I

limit of the Study Area.

I

study
and the associated

1989

the

use

to

modified

were

study
for

from this

comparison, the CUHP files
Next, a UDSWM model was
This model

the 50 sub watersheds

established

I

study
modeled in the

1989

from the

Caley Detention was not
in the new UDSWM model

of the detention elements

routing element parameters.
blcluded

the characteristics

used

To begin

. .
ImpervIOusness.
design elements.
UDSWM

Table 2-1-1-Hour Rainfall Depths

Storm Event 80th Percentile 2- Year 5-Year lO-Year 25-Year 50-Year lOO-Year 500- Year
Precipitation (in) 0.50 0.96 1.34 1.55 2.00 2.25 2.58 3.22

the

comprised slopes,
Figure A-4 in Appendix A, the Existing UDSWM Routing map,
system elements UDSWM Connectivity Diagram the

cross

side

with flat

of open channels

2.3 UDSWM PARAMETERS
The existing conveyance system is generally
culverts, bridges, and detention basins.
the location of

I

a

The UDSWM model generated

1989 study.

was essentially the same as the

of

The

the drainage

illustrates

I

is illustrated on Figure A-5 and Figure A-6 in Appendix A.

watershed

three

perform
and detention characteristics.

similarly,

and this study's 50-watershed model

1989 5-watershed model

To verify that the
additional

I

. .
ImpervIOusness

imperviousness and the current detention characteristics.
but used the

to examine the effects of

The models were updated with existing-condition
The first scenario updated the

were created

scenanos

into the drainage system and the specific
illustrate

IS

runoff

the

where

the subwatersheds connect

the routing elements

addition,

design points
connected to the next downstream design point.

In

locations.

The connectivity diagrams show where
defined at

these

I

I

-

The second scenario

imperviousness.
but also added Caley Detention to both

last

The

1989 basin characteristics

. .
ImpervIOusness,
then updated the basin characteristics to existing condition using the updated
scenario used the updated imperviousness and basin characteristics,

cases, the models produced essentially the same peak flow at Belleview.

In all

models.

in Appendix A
assigned to each
illustrating

Tabie A-i

and sireeis.

sewers,

cuiveris, siorm

I

"n")
Pictures

s

and Manning'

slope,
verified

side

length, slope,
"n" values

attributes (width,
The Manning's
"n" numbers for a sample of the

provides

imperviousness and detention
the 1989 study did not "..,
t.ll~ uetention systems projected in tl
A-4

The results from the models also supplied evidence of the effects of updated
the watershed. The

the

in the field.

in Appendix A.

included

were

conveyance elements are

conveyance
Manning's

I

I

....lticipate
1989 study
the

the

from

Uil:I.l1...,u"J 01. U~V......lUr.&..I..I."'.I.d..

I

supplies
Table A-3

Appendix
1989 study and the existing condition.
the UDSWM models. Table A-6

A

III

Table

Park, Orchard

were

I

in Appendix A
1989 study and this study. It's
was anticipated in the 1989 study
in the

1989 study.

in the

anticipated

Silo Park, Tommy Davis
for the detention elements

twice what

is roughly
is approximately 2/3 of the amount

the imperviousness

apparent from these
and the current available detention

tables that

The Design Report for
in Appendix A

Table A-3

2.3.2 Detention Elements
Four detention systems were incorporated
Hills, and Caley Detention. The storage and discharge characteristics
collected from the mapping for Silo Park, Tommy Davis Park, and Orchard Hills.
Caley Detention Basin was referenced for its storage-discharge characteristics.
lists the characteristics used in the UDSWM models.

into the existing model

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1989 STUDY
.."""ults with those calculated

I

study. The reason
implemented downstream,
and detention. Therefore, it was

1989

in the

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2.3.1 Routing Elements
The rouiing eiernenis induue open channeis,
the physical
element.

2-2

infrastructure

land use

the drainage
future

....Uu J \I. as