FLOOD11770

• County: Douglas
• Community: Douglas County
• Stream Name: Fourmile, Horse, West, Trout Creeks
• Basin: South Platte
• Title: Draft South Platte River Tributaries Hydrology Report
• Date: 5/11/2004
• Prepared For: Douglas County
• Prepared By: Moser and Associates
• Floodplain - Doc Type: Floodplain Report/Masterplan

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DRAFT SOUTH PLAITERIVER TRIBUTARIES HYDROLOGY REPORT

FOUR MILE CREEK, HORSE CREEK, WEST CREEK, AND TROUT CREEK

Table 1
2-Hour Rainfall Depths and Distribution

MINUTES 10-YEAR 25-YEAR SO-YEAR 100-YEAR SOO-YEAR
0 0.00 0.00 0.00 0.00 0.00
5 0.03 0.02 0.02 0.02 0.03
10 0.07 0,08 0.09 0.08 0.10
15 0.18 0.15 0.17 0.18 0.22
20 0.36 0.28 0.32 0.34 0.43
25 0.68 0,51 0.58 0.63 0.79
30 0.83 0.91 1.03 1.14 1.43
35 0.90 1,10 1.24 1.43 1.79
40 0.96 1.22 1.38 1.59 1.99
45 1.00 1.30 1.47 1.72 2.15
50 1.04 1..38 1.56 1.82 2.28
55 1.08 1..43 1.62 1.90 2.38
60 1.12 1..48 1.68 1.98 2.49
65 1.16 1..53 1.73 2.07 2.59
70 1.20 1..57 1.78 2.11 2.64
75 1.24 1..60 1.82 2.15 2.69
80 1.28 1..63 1.85 2.17 2.72
85 1.30 1..66 1.88 2.20 2.76
90 1.32 1..68 1.91 2.22 2.79
95 1.35 1..71 1.93 2.25 2,.82
100 1.37 1..73 1.96 2.27 2.85
105 1.40 1..75 1.98 2.30 2.88
110 1.42 1..77 2.01 2.32 2.91
115 1.44 1..79 2.03 2.35 2.94
120 1.46 1..81 2.06 2.37 2.97

UDFCD criteria states that a 6-hour d(:sign storm event should be used for drainage basin
areas of 20 square miles or more. See Appendix A. In addition, the USGS selected this
storm duration for modeling they completed for the tributary drainage areas within the
Hayman Fire Area. Therefore, the 6.,hour storm event was also selected for the Horse,
West, and Trout Creek drainage basins.

Rainfall depths for the 6-hour design storm event were obtained from the NOAA Atlas
for the 10-,25-,50-, and 100-year recurrence intervals. See Appendix A. To obtain the
50o-year rainfall depth, the procedures: outlined the in the NOAA Atlas were used. The
storm distribution of the 6-hour rainfall depth was acquired from the USGS. Table 2
summarizes the 6-hour design storm.

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