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<br />002313 <br /> <br />cfs per day. Prior to June 1990, Glen Canyon Dam releases fluctuated widely, averaging between <br />13,000 and 16,000 cfs per day. <br /> <br /> <br />Water quality monitoring at an adequate time interval was not in place directly below the dam <br /> <br /> <br />untiLaftecAugusU.98&.Therefore, evaluation of water quality changes due to daily fluctuationsJs <br /> <br /> <br />not possible for this period. However, the research flow period of June 1990 to August 1991 <br /> <br /> <br />contained several flow scenarios representative of past operations in which wide fluctuations <br /> <br />occurred. During this time, measurements of temperature and specific conductance were being <br /> <br />taken at intervals of2 hours or less. A common occurrence was a distinct fluctuation in daily <br /> <br />temperature and specific conductance as shown for Research Flow "E" during late September <br />1990 (Fig 19). <br /> <br />e. Use of alternate release structures <br /> <br /> <br />Besides the penstocks, Glen Canyon Dam is equipped to release up to 256,000 cfs. The 8 <br /> <br /> <br />penstocks account for a capacity of 33,200 cfs, discharging at 1057.66 meters (3470 feet) amsl or <br /> <br /> <br />70.1 meters below full pool. The four hollow jet tubes or river outlet works are rated to release <br /> <br /> <br />15,000 cfs at a depth of 99.4 meters below full pool or 1028.4 meters amsl (3374 feet). The <br /> <br /> <br />spillways can each release 104,000 cfs, provided the lake can adequately submerge the outlet <br /> <br /> <br />ports at an elevation of 1111.9 meters (3648 feet) or 15.86 meters below full pool. With concerns <br /> <br /> <br />of possible spillway damage, safety and power revenue losses, the alternate release ports have <br /> <br /> <br />been used sparingly. <br /> <br /> <br />1) 1965-1966 releases for filling Lake Mead. <br /> <br /> <br />The early filling stages of Lake Powell came at the expense of Lake Mead's pool level. When <br /> <br /> <br />the operation of Me ad's penstocks was in jeopardy, Glen Canyon Dam was forced to substantially <br /> <br /> <br />increase downstream discharges starting in February of 1965. The river outlet works and <br /> <br /> <br />diversion tunnels were operated in conjunction with the penstocks to discharge up to 58,000 cfs; <br /> <br />03/06/98 <br /> <br />DRAFT <br /> <br />Page 37 of62 <br />