FLOOD10336 ‎(2)‎

• County: Adams
• Community: Brighton, Commerce City and Thornton
• Stream Name: South Platte River
• Title: Flood Hazard Area Delineation, South Platte River, Adams County
• Date: 4/1/2005
• Prepared For: UDFCD; Adams County; Brighton, Commerce City, Thornton, Metro Wastewater
• Prepared By: CDM
• Floodplain - Doc Type: Floodplain Report/Masterplan

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0611\40892\PREP-FHAD\S3.00C

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Selected input parameters for the CUHP and UDSWM models for the South Platte River, Tollgate Creek, and Sand
Creek are shown in Tables 3-2, 3-3, and 3-4, respectively. The parameters are summarized as follows:

Watershed Number - See Appendix A of the Master Plan Phase A

report (UDFCD 2000)

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the diversion elements were entered as "dummy" elements, with no conveyance. However,
~lnm~nts can be modified to reflect where flow diversions from the South Platte River mainstem

Brantner Ditch
Brighton Ditch

Watershed AREA XL CAL PERIMP SLOPE
Watershed Name Number (mi2) (mB (mi) (%) (ftlft )
4400-08 528 3.05 1.40 1.48 28.0 0.005
4400-07 529 2.66 1.25 1.17 28.0 0.006
4400-06 530 3.81 3.05 2.65 28.0 0.057
4400-05 531 2.20 3.25 1.95 28.0 0.060
4400-04 517 4.76 2.75 1.85 30.0 0.046
4400-03 516 2.04 2.98 1.74 23.5 0.006
4400-02 515 4.3 2.46 3.83 35.0 0.006
4400-01 514 2.64 5.3 3.11 29.0 0.005
Westerly Creek 526 18.35 15.6 4.5 36.0 0.008

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Ditch Name
Burlington Ditch
Gardener's Ditch
Fulton Ditch

Diversion elements were included in the UDSWM model at the major
as follows:

h Element
609
610
616
747

Tributa Watershed
West Tollgate
No Name Creek
East Tollgate
Sand Creek dj s Coal Creek

UDSWM Diversion Element
900
910
915
920
930

irrigation ditch diversion points. These are

Number

Table 3-4 Sand Creek Selected CUHP In~ut

Table 3-3 Tollgate Creek Selected CUHP In~ ut Parameters
Watershed AREA XL CAL PERIMP SLOPE
Watershed Name Number (mi2) (mi) (mi) (%) (ftlft )
4405-03 658 2.41 2.34 1.52 34.0 0.007
4407-01 652 0.95 1.50 0.60 34.0 0.015
4406-01 656 3.00 3.48 1.83 34.0 0.016
4405-02 655 4.63 3.45 2.12 34.0 0.004
4405-01 653 2.58 2.91 1.85 34.0 0.005
4402-01 650 3.10 3.44 2.54 34.0 0.004
4408-01 654 2.38 6.56 2.31 34.0 0.006
4408-02 652 1.80 2.50 .833 34.0 0.006
4403-01 651 1.57 3.64 1.74 34.0 0.009
4404-01 659 1.83 4.55 2.73 25.0 0.009

Parameters

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UDSWM H

Hydrographs for the following watersheds from published studies were directly input as hydrograph elements in
the Tollgate Creek and Sand Creek UDSWM models:

Number

Second Creek
Todd Creek
Third Creek
Brighton Outfall

Tributa Watershed
Niver Creek
Iron dale Gulch
First Creek

Appendix A of the Phase A Master Plan report (UDFCD 2000) includes a complete schematic of the UDSWM
model illustrating all design points, conveyance elements, subwatersheds, and hydrograph input locations.
Hydrographs from published studies for the following watersheds were directly input as hydrograph elements in
the South Platte River UDSWM model (element numbers refer to numbering system developed for this model and
displayed in the Master Plan Phase A Appendix A schematic):

792
784
793
786

772
777

h Element

Number

- - - - ~- - - -. ------- ... -- - ---....-...-.-
Watershed AREA XL CAL PERIMP SLOPE
Watershed Name Number (mi2) (mi) (mi) (%) (ftlft)
Brantner Gulch 315 4.4 25 13.4 4.6 0.0266
Grange Hall Creek 504 9 47 38.5 32.8 0.0207
Upper SPR Watershed 0053 508 2.7 2.8 1.1 3.5 0.0068
Lower SPR Watershed 0053 509 6.8 6.13 5.3 3.5 0.0037
SPR Watershed 0055 510 9.35 25.8 13.35 11.6 0.0092
SPR Watershed 0058 511 7.6 7.5 5.4 45 0.0071
Watershed 4100 512 1.87 2.42 1.7 26.2 0.0356
Clear Creek 513 65 10.2 6.2 37.3 0.0057
Hoffman Drainaqe 518 2.9 3.4 1.7 45.0 0.02
Watershed 4000 519 4.52 6.89 6.64 45.0 0.006
SPR Watershed 0054A Upper 520 3.7 4.4 2.9 11.8 0.0108
SPR Watershed 0054B Lower 521 .8 2.2 1.2 44.3 0.0017
Watershed 0052 522 4.7 6.2 1.6 11.8 0.01
Direct Flow Area at 168m 524 1.9 2.6 1.5 2.3 0.014
SPR Watershed 0056 525 2.2 4.06 3.2 11.8 0.0203
Watershed 0001 527 0.2 1.3 0.9 2.0 0.0071

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Although Clear Creek is a lengthy and complicated watershed, it was modeled as a single basin using CUHP,
with adjustments made to the model parameters to match the published 100-year flow rate for Clear Creek
while considering the impacts on the South Platte River hydrology model.

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modified hydrograph was lagged to the South Platte River
published South Platte River peak flow at this location.

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AREA - Drainage area of watershed
XL - Distance along main flow channel from outlet to upstream boundary
CAL - Distance along main channel from outlet to watershed centroid
PERIMP - Fraction of the watershed surface that is impervious
SLOPE - Length-weighted average slope of the watershed

Tabl

3-2S

th Platte R.

S

t

d CUHP

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4/8/05

mainstem hydrograph in an effort to match the

Section 3
Hydrology