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<br />The invasion and proliferation of saltcedar and other woody plants is of <br />Considerable concern because of the danger of extreme bank stabilization and <br />resultant loss of ephemeral shoreline habitats. We recommend that a period of <br />high flows be evaluated as a means to control this vegetative overgrowth. The <br />efficacy of specific flows and the duration required to reach a certain amount <br />of vegetative scouring is presently unknown. However, we recommend that flows <br />approximating average annual historic flows of the Green River, or higher, be <br />provided for a period of at least 3 to 5 days. <br /> <br />Summer (June 22-September 22) <br /> <br />Green River flows should decrease gradually in concert with the emergence <br />of larval Colorado squawfish on spawning grounds in Yampa and Desolation-Gray <br />canyons. The flow regimen of the Green River should resemble (in timing, <br />duration) the hydrologic conditions of the Yampa River with respect to low, <br />moderate, and high wat~r flows. Gradual decreases in spring flows (e.g., not <br />more than about 14.2 m /s per day) should be in~tiated with larval drift, <br />attaining a target flow of not more than 51.0 m /s (about 1800 cfs) at Jensen, <br />Utah during the summer. Flows at Jensen should not fluctuate more than about <br />25% below the target flow on a weekly or greater basis. River flows should <br />remain at that level or attain a lower flow target for the remainder of the <br />summer. Water temperatures in the upper Green River should not differ more <br />than SaC from the temperature of the Yampa River at Echo Park, and should <br />average 22-250C in Gray Canyon from July 1 - August ]5. <br /> <br />Autumn (September 23-December 21) <br /> <br />Green River flows of about 51 m3/s (25% fluctuation below target or lower <br />and more natural regimens) should be sustained until November of each year, or <br />until most age-O Colorado squawfish emigrate from backwaters. <br /> <br />Winter (December 22-March 20) <br /> <br />Colorado squawfish, razorback sucker, and other native fishes are <br />relatively cold-adapted and are active in winter. Current winter flows in the <br />mainstream Green River reduce the availability of preferred fish habitats and <br />promote ice breakup that jams and scours these habitats. Thus the existing <br />flows are considered undesirable. It is recommended to stabilize winter flows <br />at lower levels and to maintain ice cover, once formed, until normal spring <br />breakup. Water elevations may be lower than, but not exceed ice level. Further <br />study of winter conditions and relative effects on endangered fishes and their <br />habitats remain a high priority. <br /> <br />low winter flow levels of natural streams are well tolerated by native <br />Colorado River fishes, but are generally considered detrimental to less cold- <br />adapted non-native forms. lower winter flows that better approximate natural <br />conditions should be provided and also evaluated for their potential <br />detrimental effects on introduced fishes such as channel catfish and carp. <br /> <br />32 <br />