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<br />",l"struj;ture six miles upstream, for the purpose of reducing peak discharges
<br />entering the floodway. Hydraulic studies of the existing works, including
<br />the detention dam, indicate that the floodway capacity of 110,000 c.f.s.
<br />is equivalent to a flood of 1.4 times the flood of record. This high
<br />degree of protection afforded by the large capacity of the existing
<br />floodway made it unnecessary to store the total volume of the standard
<br />proje~t flood at Pueblo Reservoir. ' ,
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<br />40. The June 1921 flood produced a peak of 87,000 c.f.s. and a
<br />volume of 93,000 acre-feet at Pueblo damsite. The volume is equal to
<br />.38 inch of runoff from the 4,670 square miles of drainage area. This
<br />flood was selected as the basis of design for the flood control storage
<br />at PueblocReservoir. The volume of the flood,has a recurrence interval'
<br />of about 100 years. Flood control storage in Pueblo Reservoir equal
<br />to the .v<;llume of the design flood in conjunction with the existing
<br />Pueblo Floodway would provide, the city of Pueblo protection against
<br />Arkansas River floods exceeding standard project magnitude. An opera-
<br />tion hydrograph of the design flood is shown on plate 4. In addition
<br />to the summer requirement of 93,000 acre-feet of flood control storage,
<br />there will be a winter requirement of 27,000 acre-feet of flood control
<br />storage that will be held inviOlate for possible winter floods. The
<br />27,000 acre-feet of winter' storage 'was derived from the June 1921 storm.
<br />This. computed amount of storage would have been necessary if the storm
<br />had occurred in late March or early April. The total flood runoff was
<br />stored without releases during the period of inflow. The flood control
<br />storage will not be depleted by sediment during the life of the project.
<br />As sediment accumulates in the reservoir, adjustments will be made in
<br />the storage allocated to the conservation pool. That will assure the
<br />93,000 acre-feet of flood control storage for the life of the project.
<br />, Pc,rtinent design data for Pueblo Reservoir are shown in table 3.
<br />
<br />",TABLE 3. -- Pertinent Design Data, Pueblo Dam and Reservoir
<br />
<br /> CaDaci tv
<br /> Pool Elevation (Acre- (Inches of
<br /> (feet above m.s.l.) feet) runoff)
<br />Top' flood control pool 4,898.74 " 357,000 -1.43
<br />Top of winter joint use pool 4,893.65 - 329,000 1.32
<br />Top conservation pool 4,880.6 264,000 1.06
<br />Top inactive pool 4,796.7 30,000 0.12
<br />Flood control storage 4,880.6-4,898.74 93,000 0.38
<br />Conservation storage 4,880.6 234,000 0.94
<br />Inactive storage 4,728.4-4,796.7 30,000 0.12
<br />Note: The 100- ear sediment roduction of 103 100 acre-feet WIll
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<br />be deducted from the 234,000 acre-feet conservation pool as it accrues.
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