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<br />OOZ3JO <br /> <br />3. Historic Patterns seen at Lake Powell <br /> <br />In the following discussion, We found it useful to use a ranking system to compare lake <br /> <br />attributes and reactions against such outside factors as total inflow or outflow for the year, <br /> <br />coldness of winter, hotness. of surnmer.A-tab1eoHhese rankings is found in the appendix. <br /> <br /> <br />a. Filling Period (1963-mid 1970's) <br /> <br /> <br />While Lake Powell did not reach full pool until 1980, by 1973 to 1975 it reached a level of <br /> <br /> <br />normal fluctuations. By the mid-1970's most of the indicator parameters (temperature, <br /> <br /> <br />conductivity and dissolved oxygen) had stabilized. This early period of filling was characterized <br /> <br /> <br />by low lake volume and reduced releases, resulting in a higher exchange rate for the water within <br /> <br /> <br />the lake: between 124% to 380%. This indicates that the entire lake's water quality was more <br /> <br /> <br />rapidly dictated by inflow water quality than in subsequent periods, and such was the case in the <br />1960's. <br /> <br />Interpretation of this period is hampered by erratic data collection--there are holes in <br /> <br /> <br />temperature and dissolved oxygen data at critical junctures, as well as irregularities in the <br /> <br /> <br />temporal sampling. Some conclusions can still be drawn from this period. <br /> <br /> <br />One of the signatures of this filling cycle was an 8th ranked flood (the 8th highest annual <br /> <br /> <br />inflow' in Lake Powell's history) in 1965. This tremendous volume of water appeared at the dam <br /> <br /> <br />with the lowest conductance values recorded since the lake's filling. This plume of fresh water <br /> <br /> <br />shows clearly in Fig. 3a and the longitudinal plots of Fig. 4, but doesn't have the diluting effect <br /> <br />that one could expect from the mass it represents, for it is flushed from the lake within 2 years. It <br /> <br />is apparent is some of it is mixed into the hypolimnion by early 1966, but by 1967, the fall <br /> <br />SWARM plug has substantially salinized the lake. In spite of the high volume turnover rates for <br />the 1960's, this extremely salty hypolimnion (values up to 1300 ~S/cm) developed with only one <br />season's inflow, but required 5 \!'years to dilute to previous levels. One reason is the nature of the <br /> <br />03/06/98 <br /> <br />DRAFT <br /> <br />Page 24 of 62 <br />