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<br />002546
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<br />dam releases, was calculated at 7,350 cfs for the years of data the dam was fuBy operational.
<br />However, dam operations regulate the outflow from Pueblo Dam to maintain flows, as much as
<br />possible, to below 6,000 cfs at the Avondale gage, approximately 30 miles downstream (BOR,
<br />1981). Log Pearson's Type III analysis is not entirely applicable to regulated flows, but is used
<br />here to show magnitude level effects of the dam. Wildhorse Creek flow estimates were taken
<br />from FEMA (1986) where intermediate values were interpolated and low values were
<br />extrapolated. The extrapolated value for the 1.25-year flood is 480 cfs. This may be high as a
<br />result of the flashy runoff nature of the creek. Wildhorse Creek is the only major drainage
<br />between the dam and the Moffat SI. gage. The analysis of data for this gage related the 100-year
<br />return flood at only \2,500 cfs; however reports from FEMA (1986) consider the \ OO-year return
<br />flood to be 20,000 cfs and was accepted in this study. The Moffat Street Gage represents flows
<br />through the concrete levee section. This levee is considered to have a capacity of 110,000 cfs,
<br />which reprcscnts a much higher level of flood protection than existed when the levee was
<br />originally constructed, Although a 103,000 cfs flood occurred in 1921, it is considered a 1,000-
<br />year flood event and pre-dated the dam. The dam is currently expected to control the 500-year
<br />event (FEMA. 1986), Flood events have been greatly reduced for all recurrence intervals since
<br />the construction of Pueblo Dam. The magnitude effect of the darn on flood flows is presented in
<br />a comparison of pre- and post-dam data compiled in Figure 2-7.
<br />
<br />Table Z-12 Flood Peaks ror Ihe Arkansas River, Fountain Creek and Wildhorse Creek
<br />
<br /> Arkansas Rhter Wild horse Creek Fountain Creek
<br />Return Abo\'e Pueblo Moffat Street Near Pueblo Near Pueblo
<br />Period Gage Gage Gage Gage
<br />(Years) (efs) (efs) (efs) (efsl (ef;)
<br />1.25 3.030 3,570 4,480 00480 Z,070
<br />2 4.2Z0 4,830 6,930 001.300 5,170
<br />5 5,460 6.680 11.800 "3,400 11,500
<br />10 6.070 7,990 16.Z00 '5,700 16,800
<br />20 6.560 9,300 21,400 "9,200 ZZ,400
<br />25 6.690 9,730 23,300 0010,500 24,300
<br />50 7,050 11,100 30,100 '14,000 30,300
<br />\00 7,350 'ZO,OOO 38.300 '19,500 36,600
<br />500 7,880 '40,000 64.600 '39,500 52,100
<br />Period of Record 1975-1999 1989-1999 1895-1975 1922-1999'"
<br />
<br />. FEMA,1986
<br />00 Extrapolated from FE:"vIA. 1986
<br />... Record IS intermIttent: 1922.1925,1940-1965,1971-1999
<br />SOllrce: USGS Online. 20UO
<br />
<br />Arkansas RIY~r FIsherIes HJbllJ,1 R~slorJ.tion. Pueblo. Colorildo
<br />Final ECOSySlem RestorJllun Rt:pun Jnd EnVIronmental Assessment
<br />11-34
<br />
<br />Chapter II. Envlfonment::ll Sell1ng
<br />September 200 I
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