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<br />Chapter I Purpose and Need 8 <br /> <br />dam. The planning report/final environmental statement was prepared. It concluded that <br />there would be no significant adverse impacts to the environment. The facility has been <br />installed and initial testing is underway. <br /> <br />Hungry Hone Dam Selective Withdrawal System - Near-constant, cold-water releases <br />(40C) were found to be causing fish losses below Hungry Horse Dam. Temperature <br />modifications at Hungry Horse Dam have been completed. The modifications and <br />temperature objectives are very similar to those proposed for Glen Canyon Dam. River <br />temperatures will be increased to about I rc in mid-sununer to promote higher growth rates <br />in cutthroat trout. The Hungry Horse Dam Selective Level Withdrawal System Final <br />Environmental Assessment/Finding of No Significant Impact (Reclamation 1994) states that <br />warmwater releases would increase the downstream trout growth rates by two to five times. <br />Modeling studies indicate that phytoplanton and zooplankton would be entrained in the <br />discharge, but that overall productivity in the reservoir would increase somewhat. <br />Warmwater discharge would destabilize the temperature stratification of the reservoir, <br />promoting a stronger turnover, cycling more nutrients into the surface water. Some minor <br />impacts to the lake fishery are expected, but are thought to be avoidable through careful <br />operation. Fish entrainment in the turbines is not expected because fish stay near shoreline. <br />The report concluded that no adverse impacts would be expected from the addition of <br />temperature controls. <br /> <br />Other Selective Withdrawal Systems - In the Upper Colorado Region of the Bureau of <br />Reclamation, Jordanelle, Stagecoach, and McPhee Dams were a1] originally designed with <br />temperature controls so that river temperatures could be regulated to maintain natural <br />conditions and sustain trout fisheries. All of these have fulfilled their intended purpose <br />without any known ancillary impacts to either the reservoirs or rivers below them. <br />