FLOOD10207

• Designation Number: 503
• County: Jefferson
• Community: Unincorporated Jefferson County
• Stream Name: Woman Creek, Walnut, Upper Big Dry and Rock Creek
• Basin: South Platte
• Title: Drainage & Flood Control Master Plan - Rocky Flats Plant
• Date: 4/1/1992
• Designation Date: 9/1/1999
• Floodplain - Doc Type: Floodplain Report/Masterplan

Data Included

General

TABLE 11-1

1.

Design storms for the outfall study hydrology were developed following the
procedures outlined in the Urban Storm Drainage Criteria Manual (USDCM)
(Wright McLaughlin, 1969). The USDCM specifies the temporal distribution
for a 2-hour design storm developed from the I-hour National Oceanic and
Atmospheric Agency (NOAA) precipitation depth. This design storm
approximates a maximum runoff rate from a catchment area of less than 5
square miles in the Denver region. No areal adjustment of the NOAA point
precipitation depth is required for catchments of this size. Design storms were
developed in this manner for the 2-, 5-, 10-, and l00-year frequencies and are
presented in Table 11-1 of the document. These design storms were identical
to those used in the Westminster Flood Hazard Area Delineation (FHAD)
hydrologic modelling.

DESIGN RAINFALLl

2. CUHP /SWMM input parameters and output flows and storage volumes are
listed in the Technical Appendix of the document for the 2- and lOG-year
design storms.

............. .'filne. Fro';' ..... . ........................................................ ..... ......... ...... ............>...... ............ i. .........
............~..Dllig of.... .>.>........ . IuCftDleatollJtiptll(l.r. ii ........ .i
..................> ........... .......
.... ..Shmll...... ......... ........... ........ ..~~,,_............ ....
............................ (ininutesl . ... ...... ..... 2-Yeai' 5-Vear ....11-'1'.,....
.............. ...... .... FreijUendeS" ... ......>.~ F..iid ....
.................. ............FrelJUenel!ill . .......~.ts ...
5 .02 .03 .03 .03
10 .04 .05 .06 .08
15 .08 .12 .14 .12
20 .16 .21 .25 .21
25 .25 .35 .42 .38
30 .14 .18 .20 .67
35 .06 .08 .09 .38
40 .05 .06 .07 .21
45 .03 .05 .06 .17
50 .03 .05 .05 .13
55 .03 .04 .05 .11
60 .03 .04 .05 .11
65 .03 .04 .05 .11
70 .02 .04 .05 .05
75 .02 .04 .05 .05
80 .02 .03 .04 .03
85 .02 .03 .03 .03
90 .02 .03 .03 .03
95 .02 .03 .03 .03
100 .02 .02 .03 .03
105 .02 .02 .03 .03
110 .02 .02 .03 .03
115 .01 .02 .03 .03
120 .01 .02 .02 .03
. ...... ...... .. .. ........ ....... ~ .......................................
TOTAL 1.15 1.60 . 1.8!l .. .... ;J.Oll.. ....

3. Peak discharges from Great Western Reservoir are 80 cfs for the 2-year storm
and 1,940 cfs for the l00-year storm. Peak discharges from Standley Lake are
60 cfs for the 2-year storm and 1,470 cfs for the lOG-year storm.

4. Table 11-1 of the document, presented herein, presents the sub-basins with the
CUHP /SWMM model elements. Line diagrams for the models are included
in the Technical Appendix.

1. This report presents fully approved hydrology for Walnut Creek and Big Dry
Creek downstream of Great Western Reservoir and Standley Lake. New
hydrologic studies should be consistent with this report unless changes are
coordinated fully with UDFCD.

2.

The 1986 Technical Appendix (10/15/86 computer runs) indicates that the
lOG-year inflow flood to Great Western Reservoir is the same as the 100-year
outflow flood of 1940 cfs. It would appear that surface detention storage was
not considered. II

I Taken from "Outfall Systems Planning" (Muller Engineering, 1987).