FLOOD09310

• County: Adams
• Community: Adams County
• Stream Name: Todd Creek
• Basin: South Platte
• Title: Flood Hazard Area Delineation
• Date: 12/1/1985
• Prepared For: Adams County
• Prepared By: UDFCD
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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peak discharges for hydraulic analysis. Figure 1 shows the basin and
sub-basin boundaries.

TABLE I
SlI4MARY OF DISCHARGES
TODD CREEK

The basi n and unit hydrograph parameters are tabul ated in Table I!.
The procedure used to determine the CUHP parameters is outlined in the
Runoff Chapter of the Urban Storm Drainage Criteria Manual (USDCM). A
schematic of the SWMM routing network is shown in Figure 2. The SWMM
conveyance element parameters were estimated using the project
mapping, from field observations, and from discussions with the UDFCD,
and are listed in Table III. Detailed documentation of the hydrologic
analysis is available at the office of the UDFCD.

Design (1) Drainag~ Discharge (cfs)
Location Poi nt No. Area (mi ) 10-yr. 50-yr. 100-yr.
Todd Creek Mouth 1 7.84 2840 6140 8360
Todd Creek D/S of Havana Street 2 6.79 2900 6140 8190
Todd Creek D/S of Tributaries
1 and 4 Confluence 3 6.32 2940 6120 8020
Todd Creek U/S of Tributaries
1 and 4 Confluence 4 4.04 1780 3780 4990
Todd Creek D/S of Tri butary 2
Confluence 5 2.99 1670 3310 4280
Todd Creek U/S of Tri butary 2
Confluence 6 2.01 1100 2170 2800
Todd Creek D/S of Tri butary 3
Confl uence 7 0.94 770 1490 1900
Todd Creek U/S of Tri butary 3
Confluence 8 0.60 480 930 1190
Todd Creek at U/S Study Limit 9 0.34 310 600 750
Tri butary 1 at Confluence With
Mai n Stem 10 0.59 370 760 990
Tri butary 1 at U/S Study Limit 11 0.34 180 350 430
Tributary 2 at Confluence With
Main Stem 12 0.98 600 1200 1540
Tributary 2 at U/S Study Limit 13 0.30 390 680 830
Tributary 3 at Confluence With
Main Stem 14 0.34 290 560 720
Tributary 3 at U/S Study Limit 15 0.18 170 330 420
Tributary 4 at Confluence With
Main Stem 16 1.69 920 1820 2360
Tributary 4 at Yosemite Street 17 1.21 980 1760 2190
Tributary 4 at U/S Study Limit 18 0.18 220 400 500

Impervi ousness (I ) for each sub-basi n was estimated for future 1 and
a
use conditions. At the time the hydrology modeling effort was
underway, future 1 and use for the City of Thornton had not yet been
resolved. To avoid delay in the hydrology modeling, the Project
Sponsors agreed that a meeting with the Planners from Thornton,
Brighton, and Adams County would be conducted to determine the
probable future land use based on the best available information.
Because of the uncertainty of this future land use, efforts were made
to show reasonable percent impervious land cover within the basin.
This is shown on Figure 1. Future land use will hinge largely on the
final alignment of E-470, and at this time it is thought E-470 will
traverse the upper portion of the Todd Creek Basin. The Project
Sponsors have agreed thi s wi 11 probably resul tin greater commerci a 1
development adjacent to thi s hi ghway than is shown on the Thornton
Comprehensive Plan currently under revision. The projected commercial
development will be less dense than typical urban commercial, with the
aim to achi eve a "campus-type" offi ce park envi ronment. Ia val ues are
listed with the other CUHP parameters in Table II.

One-hour point rainfall depths were determined from the Rainfall
Chapter of the USDCM for the 10-, 50- and 100-year return periods.
These values were used to develop the two-hou r des i gn storms based

(1) Refer to Figure 1

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