FLOOD00704

• Designation Number: 188
• County: Lake
• Community: Unincorporated Lake County
• Stream Name: Arkansas River, Lake Creek, Evans Gulch
• Title: Floodplain Information Report - Arkansas River, Lake Creek, Evans Gulch
• Date: 11/1/1981
• Designation Date: 4/1/1982
• Floodplain - Doc Type: Floodplain Report/Masterplan

Lake Creek

TABLE 9
tAKE CREEK DISCHAR(;I':, DATA
Drainage Peak Dischar~es (cfs)
Description Area (Sq. Mi.) 10-YR 50-YR 10 -YR 500~YR
1. DOWIHltream LimIt 64.0 2390 2975 3210 3740
2, Dvwnstream of
Crystal Lake Creek 64.0 2390 2975 3210 3740
3 ' Upstream of
Crystal Lake Creek 59.1 2275 2815 3040 3535
4, Downstream of
Echo Canyon Creek 58.3 2275 2815 3040 3535
5, Upstream of
Echo Canyon Creek 55.9 2205 2725 2940 3415
6, Upstream Limit 55.4 2205 2725 2940 3415

For Lake Creek flood fl.~..' frequency analyses of streamgll.ge
records using the procedures outlined in Water Resources Council
Bulletin 17 were used (Reference 10). The first analysis
consisted of analyzing streamgage information at gagt. 07084500
located 3.0 miles downstream 'Jf the study site for the period
1946-1980. The streamgage informatiC)n inc1ud"d all diversL'ns
into the Lake Creek Rasin through ~'in Lakes Tunnel No.1.
The second method utilized the streamgage records and
corresponding Tunnel flows to cleve lop a frequency curve for
I.1nregulatecl conditions (useful for c..:>mparis'Jn purposes with other
basins). To thb fr..ql.1ency curvt' for unrt'gulated c.,:,nditions
maximum capacity tunnel flows were added to develop the regulated
frequency curve. Although the streamgage and Tunnel are located
7.0 miles apart, no adjustments were made for attenuation between
the gages since available Tunnel records indicate that diversion
fl,lWS normally remain constant for several days on and prior to
the date of the peak flow at the streamgage site, thus roinirnizing
any attenuation effects.
Comparing the results of the two frequency studies, it '''''s found
that the second method produced discharges from 7 11% higher
than the first method. Rev!e'.. of the Tunnel flows show that
these flows have increased, on the average, 26% since 1971, as
compared to the perivd 1946-1970.

The Tunnel flows nre now approaching the maximum Tunnel
of 625 cfs. This indicates that the second method which
the 625 cfs diversi,)n is the pl:"f'ff'rahl" method (}f
analyses.

capacity
includes
the two

Comparison of the above results ...ith other analyses in the basin
Olhow poor agreement. The Lake Cr~ek watershed, due to its
steepness, high percentage of rock cutcrop in the higher
elevatiolls <1m] its spa.rcity ')[ ve8eta.tl')11, produces a larger
volume and quantity of sllowmelt runoff than would normally be
expected from the other hasin~ which were used in this
comparison. The Lake Creek results, therefore, appear
reasonable.

Evans Gulch

KnO'w'ing the f~""d f~"",s at thc gagc site, thc diser.<l1:gcG ....ere
transfered to the studv site using tl'w transfer equation fr<lID
T.'1-1 (Reference ll); .

Qsite -(Asite I A~age )0.79 x Qunre~uIated + 625

For Evans Gulch, the peak discharges for fl00ds .~f the 10~, 50-,
100-, and 500-year recurrencE' intervals ....ere computed using
T.'1-1 (Reference 12). The suppvrting calculatbns sre sho"m in
the Hydrology Report and the results are as follo....s;

Where; Q - diOlch..rge in cis
A - drainage area in square llliles
Agage ~ 75 square miles

The exponent of the ,,'ql.lution ;.'8S Olubstantiated by previous w0rk
by the Water and P"wer Resources Sf'rvice (Reference II). The
peak discharges calculated for the study reach are as fol1vws:

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