FLOOD10334 ‎(2)‎

• Designation Number: 588
• County: Arapahoe
• County: Jefferson
• Community: Littleton
• Stream Name: Massey Draw and SJCD (South)
• Title: FHAD - Massey Draw and SJCD ‎(South)‎
• Date: 12/1/2005
• Prepared For: Urban Drainage and Flood Control District, Jefferson County, Littleton
• Prepared By: Olsson Associates
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Flood Hazard Area Delineation
Massey Draw and SJCD (South)
December 2005

City f!l Littleton

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Mode

Baseline
Percent Model
Difference I 0100 (cfs)

Table 4 - Comparison of 100-Year Flows:
Target Flows, Calibration Model and Modified Baseline
Original Original
Plan Plan
Design Subwater-
Point sheds

Calibration
Model
0100 (cfs)

Target
0100 (cfs)

Location

OA
Design
Point

Model Calibration

For the main stem of Massey Draw, the models were calibrated to approximate the future land-use
conditions peak flow rates as reported in the UDFCD memorandum dated February 28, 1985,
(Reference 8) and presented in Table 2,

3.8

LI

t

",..,......,...,...,',...,',.,...,.,.,......,...'..."1

l..~:~~~....l
--I
\..,."..~,QJ,'~.."...,'

2%
6%
2%

~9.~?~yJ2r.~'!!---.--------.---".,.".,"",... .'.'.'..'.'''-'.'.'.'-..-'--...'''-.-------------..'--
.____Jg,:L__J 13 L...... F....J H09E9Q.l._______
139 L____1L__l.... D2 ,LL____Q9Er:i~.<?r.!.__,___
110 L...._1J...,' 01, D2, F;_.Y'l9d?'!!9rth

Flows Reported in UDFCD Memorandum
100- Year Peak Flow

~,.9?Qgf?
~.?1.9..~f?
2,920 cfs

100-Year

__IjQgI:?9Q~ "......._'''_''
Garrison Street
Wadsworth Boulevard

Table 2-
Location

I

549
--
; 1,181

-4%
29%

,I

_"_______~_m____.._.
946

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I

1

573
284

1 ,041
719

-10%

3%
0%
-4%

-8%
1%

I

821

?,??~
2.879

The 1 OO-year flows from the calibration model matched reasonably well with the target flow values.
On the North Tributary of Massey Draw, the flow from the calibration model was 29 percent greater
than the target value at Wadsworth Blvd. This difference was due, in part, to the larger watershed that
was delineated and discussed previously in this report.

1

13%

5%
-5%

.--....-.-.---..--.--..-..........-------.

NQrth",I.~il:?,~~~-ryJ~~~.9-??-~y"'p,~,~'!!, "L._,___.__,___..________..____.__i
142 10, C2 Garrison
.-----_.. -
151 ~ 9 __ C1, C2 Wadsworth l

~~--~ ----.--.
. ~,
SJ CP_(~.9~..t~.LN_<2rth_I~il:?lJ~~ry..,._",L-.--------------,------__________,I_____L___,_____________...-3
,J.,O~"..,_g__f..!.,"~,'".g""',.".....,._fS~Qg9ryL...__,_119.,50 _,.., ,~4?"

sjc'D'~~{So~l..9_!J~LIrjbutaries ________._ r-==~==~,
166 i 8 ' E 1 Garrison 708 729,
- .' .-
___.....,__._,...,.............__.'................_..__'..._.._......_......_ .mm.m~..........___..._..._._...__......m'..'..._.._. ..............-.........-....-.... _ -............-....... ............................-
265 i E2 , E2 ! Garrison i 283 ! 284 ..
..._______..___..__........___.___...._'._'..._..._.................__."'_'''''' ..~___._.._...._..__......__m.___..__._ _ ___.....................m..
. J~~___ j 7 l~1L~~~___,Garr~~Q.Q______,_____._999_____,__~~?....._
169 ! 6 i B 1, E 1, I I i
! E2 ' Wadsworth l l
259 ! B2 B2 Wadsworth i
---~-54 ---!---~---~-'B'1':-B2-,--'---'-------~-' ;-----
; ; E1, E2 Confluence i
_:73_ J 3 IA'Err'E~~I~cfI~e ~~

99 ' l' 'Confluence'

.----.--.--..---.
549
1,181

._...m.........,.._.
572
919

For the tributaries to Massey Draw, and for SJCD (South), the 100-year peak flows were calibrated to
approximate the flows as reported in the Flood Insurance Study (FIS) for Jefferson County (Reference
7) and presented in Table 3,

udy

from Flood Insurance St
I 100- Year Peak Flow

1..dI.L.__
719
.-.-...---..

1 ,484
714

._..._._.. mm.mm.._...'....._,......._..__..____._
570 cfs
______H_
920 cfs

1,?~!5",~f?
~,4.4Qgf~

.. S~~QJ~Qy!,Qlt-!9_~b_I~jqlJ!~ryT_
Newland Street I

Table
Location
..~,9~?~y,Pr9'!!.!t-!9rthIr!l:?lJ~9ry.
Garrison Street
Wadsworth Boulevard 1

ows

FI

ear

100- Y

3

.~~gpj~_QY!h) -..."
Wadsworth Boulevard
._._..___.........m..__..._...._......_mm._m...............m._......,....._...._............._.......
,.~QlJ~Q,,~,19~t_~g9Qy9QBQ~9,

, 2,151

L,?!!5.;?__-.
i 3.166

896

2,441
3.314

1,

Results

3.9

700 cfs

The calibration model included two existing detention basins that are located west of the hogback on
Massey Draw. These detention basins were included in the model that was prepared for the 1985
UDFCD memorandum. The model was calibrated by varying the time to peak coefficient (Ct) and the
unit hydrograph peaking coefficient (Cp) to approximate the100-year flow rates at select locations,
Table 4 shows a comparison of the 1 OO-year flows generated from the FIS, the 1985 UDFCD
memorandum and the calibration model.

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The existing detention on Massey Draw, upstream of South Carr Street, and on SJCD (South)
upstream of South Kipling Parkway at "The Meadows Sanctuary," was added to the calibration model
to create the baseline model. These ponds are publicly owned and maintained and are recognized by
UDFCD. They were added to the baseline model to reflect the existing conditions in the watershed,
The baseline model for Massey Draw differs from the model presented in the April 2004 Hydrology
Report. Modifications to the original baseline model contained herein were made to incorporate flow
patterns observed during the June 27, 2004 flash flooding event. Refinement of the subwatershed
delineations and routing affected the timing of the flows, resulting in slightly higher peak flows.

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