FLOOD10348

• County: Clear Creek
• Community: Clear Creek County
• Basin: South Platte
• Title: Hydrological Analysis - Type 15 FIS - Clear Creek County
• Date: 9/1/1990
• Floodplain - Doc Type: Floodplain Report/Masterplan

TABLE 2
6-HOUR ACCUMULATED POINT RAINFALL VALUES
CLEAR CREEK BASIN

Frequency
(years)

Rainfall
(inches)

Adjusted Rainfall
(inches)

2
5
10
50
100
500

0.9
1.2
1.4
1.8
2.0
2.4

0.70
1.02
1.24
1.59
1.77
2.12

TABLE 3
6-HOUR HYPOTHETICAL STORM DISTRIBUTION
CLEAR CREEK BASIN

Time
(Min)

30
60
90
120
150
180
210
240
270
300
330
360

Rainfall Intensity ( inches/hour) for specified
Recurrence Interval
2-yr S-yr lo-yr SO-yr lOO-yr SOO-yr
0.02 0.03 0.04 0.04 0.05 0.06
0.03 0.04 0.05 0.06 0.07 0.08
0.04 0.06 0.07 0.08 0.09 0.11
0.06 0.09 0.10 0.12 0.14 0.17
0.10 0.15 0.18 0.22 0.25 0.30
0.24 0.35 0.42 0.55 0.60 0.72
0.58 0.81 1.05 1.42 1. 53 1.83
0.15 0.22 0.26 0.32 0.36 0.44
0.07 0.11 0.13 0.16 0.18 0.22
0.05 0.07 0.08 0.10 0.11 0.14
0.03 0.05 0.06 0.07 0.08 0.09
0.02 0.04 0.04 0.05 0.06 0.07

Five existing reservoirs were included in the SWMM. Four
of the reservoirs are located on South Clear Creek and the fifth
is located on Clear Creek downstream of South Clear Creek near
Georgetown. Reservoir storage and outflow was determined using
the equation for discharge over a rectangular weir. Assumptions
used in determining the reservoir storage and outflow were that
1) the surface area of the reservoirs .shown on the quadrangle
maps correspond to the water surface elevation at the crest of
the spillway; 2) the slope of the surrounding area is so steep
that the lateral surface area increase is negligible and 3) the
reserviors were assumed filled. to the crest so that the only
effects in reducing flows was from surcharge routing and not
detention. Table 4 lists reservior characteristics.

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