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The past helps project the future. As the Powell filled from 1968 to 1974, the temperatures moderated from the high seasonal swings to cooler, more consistent patterns. Once the lake rose above about 3630 ft elevation, the temperatures appeared to fall into the typical post-dam, post-filling pattern. The inflow hydrograph also plays an important part in determining dam release temperatures. A large spring inflow event (the blue line at the bottom) introduces a large volume of warmer water to the reservoir, initially to the surface, which mixes with lower layers of the lake over subsequent years. In general, lowering lake levels allow for warmer surface waters of the lake to be discharged through the dam. The western U.S. has sustained drought conditions since 1999, resulting in diminishing lake elevations and a thinner epilimnion. In 2003, lake elevations have fallen below 3630 ft to 3604 ft, reaching the lowest levels since 1973. This has resulted in some of the highest summer release temperatures since 1972. |
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