FLOOD05818

• County: Jefferson
• Community: Golden
• Stream Name: Clear Creek
• Basin: South Platte
• Title: Hydrology Study of Clear Creek Between Wadsworth and Federal Boulevard
• Date: 4/1/1977
• Prepared For: Jefferson County
• Prepared By: Colorado Division of Highways
• Floodplain - Doc Type: Floodplain Report/Masterplan

r 76-1(35) PE

TABLE I
YEARS OF DRAINAGE AREA-SQ. MI.
GAGE NO. STREAM/LOCATION RECORD TOTAL BELOW 7500 FT.
6-71 05 Bear Creek at Morrison 62 164 30
6-7110 Turkey Creek near Morrison 11 50 16
6-7220 North St. Vrain at Longmont 28 106 14
6-7295 South Boulder Creek near
[to 1955) El dorado Spri ngs 6D 109 13
6-7330 Big Thompson at Estes Park 25 137 19
6-7420 Little Thompson near Berthoud 16 101 46

Figure No. 4 is a plot of drainage area versus Q1DO for these gages.
Both the total drainage area and the drainage area below elevation
7500 feet are plotted. The 7500 foot criteria has been established
by McCain2 to delineate snow melt from rainfall peak flows.

From Figure .No. 4 it is apparent that a conservative discharge prediction
could be obtained by giving more weight to Gages 6-7105, 7195, and 7420.
Gage 6-7420 shows the highest results for drainage area below 7500 feet,
but this gage had only 16 years of record. It had a skew coefficient of
0.6384, which is Inuch higher than the regionalized coefficient of -0.15,
published in Bulletin No. 17.3 Therefore it is considered less reliable
than Gages 6-7105 and 7195. Using the regionalized skew coefficient,
Gage 6-7420 gave Q100 = 13,800 cfs, which is in line with Gages 6-7105
and 7195.

Technical Manual No. 1.2 - The peak flow predictions using the regression
equat10n 1n th1S Manual at four selected points along Clear Creek are:

LOCATION

DRAINAGE AREA - SQ. MI.
TOTAL BELOW 7500 FT.

Q100*

11 ,300 cfs

19,300

24,000
26,400

TABLE II

Golden (at Gage 6-7195) 399 23
Above Ra 1 s ton Creek confluence 454 76
Below Ralston Creek 543 122
At Mouth (at Gage 6-7200) 575 153

* These predictions based on drainage areas below 7500 ft. elevation.

2 J. F. McCain and R. D. Jarrett, "Manual for Estimatin9 Flood Characteristics
of Natural-Flow Streams in Colorado", Technical Manual No.1, Colorado
Water Conservation Board. (1976). 68 pp. -- -

3 United States 'Water Resources Council, "Guidelines for Determining Flood
Flow Frequency", Bulletin #17 of the Hydrology Committee. (March 1976)
p. 9-6.

6