9374 - Laserfiche WebLink

Home Browse Search

. Nursery backwaters we periodically scoured in winter by lateral chute channels that flow around mid-chann I ice jams. . All backwaters remai ed suitable over winter with respect to water chemical parameters (temperatur and dissolved oxygen). . Approximately 50% 0 backwaters in the middle Green River became unsuitable during two mild wint s as a result of ice jams that caused damming and flow- through, reduction of ater depth from ice development and collapsing ice lenses, or unexplained local cannel changes that caused flow-through. . Loss of backwater- sui bility during winter may force fish to leave these sheltered habitats at greater risk f predation with presumed energy expenditure. COMMENDATIONS I , 0 allow for maximum surface ice develo ment laming Gorge Dam in a manner that protects and enhances do pikeminnow. If air temperature were predictable, stable dam releases during a cold inter would allow for rapid development of an ice cap of sufficient thickness to minim ze occurrence of ice jams and frazil ice development. Onc€; the ice reached a certain thi kness, it would be theoretically possible to resume some fluctuations beneath the ice cap without disrupting it. The vertical rise in river stage necessary to break an ice la er is approximately three times the thickness of that layer (Donchenko 1978). Accordi g to calculations by Valdez and Masslich (1989), in a severe winter, a critical ice thickne s of 15 cm would have to be reached near Jensen to resist anticipated stage changes 0 45 cm under maximum hydropower production at Flaming Gorge Dam. At maximum ic development potential, this ice thickness could be reached in about 3 days (Calkins 1979). The effect of river fluctuations on backwaters beneath surface ice is not known. This scen '0 is strictly theoretical and not recommended until there is a better understanding of ice p ocesses in the Green River relative to dam operations. "') Minimize chan e in volume and fluctuations durin the winter riod. Winter releases from Flami Gorge Dam should be maintained at the same flow range as in the immediately precedin summer and fall. This flow scenario should be maintained until March 1, a time when e ly low elevation runoff from tributaries usually increases river stage in the nursery area, in ependent of dam operations. 3. Maintain ersistent and stab e nurse backwaters. Maintaining similar flow Ie els throughout summer, fall, and winter will help to stabilize backwaters and reduce fore d movement of fish in search of alternative backwaters at the presumed risk of excessive nergy expenditure and predation (Bestgen et al. 1998, Schmidt 1996). Changes in release volumes from the dam that either flood or desiccate nursery 24 ,I