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<br /><~--.. <br />;4J <br /> <br />a test to measure responses of the fluvial ecosystem and related resources. One of the critical <br />observations will be to see if flow at the test level of 1275 cms for 7 days has the ability to <br />move sediment from the channel and deposit it along the channel margins and banks. Rebuilding <br />of channel margin deposits rejuvenates the system by providing substrate for woody riparian <br />species. This should result in long-term benefit to the habitat of southwestern willow flycatcher <br />in the Grand Canyon. The dates for conducting the test flow will also avoid enhancing <br />regeneration of tamarislc, because tamarisk will not be in seed at this time. As discussed above, <br />the ramping rates selected will help maintain, as possible, newly deposited sediments along the <br />channel margins. <br /> <br />If the test is successful, some nesting and foraging habitats of southwestern willow flycatcher <br />would be affected in varying degrees in the short-term. The degree and nature of that short-term <br />loss concerns the Service due to the small size of the population range-wide and the downward <br />trend of the Grand Canyon population. In response to the Service's request for more <br />information regarding potential direct affects, Reclamation analyzed four sites in the Grand <br />Canyon that have been occupied consistently by the southwestern willow flycatcher and provided <br />the following information (U.S. Bureau of Reclamation 1996a): <br /> <br />1. Determine nest tree and nest height elevations in relation to local stage discharge elevations:" <br />Nests were reported to be 2: 3.4 m up in tamarisk trees and> 3 m above the 1275 cms stage. <br />Root crowns at two sites might be inundated as much as 0.5 m, but erosion of those trees is not <br />anticipated because they exist in densely vegetated sand bars. Observations of a similar release <br />in 1980 when Glen Canyon Dam spilled for the first time are reflected in this conclusion. <br /> <br />2. Determine changes in vegetation cover on southwestern willow flycatcher habitat patches from <br />the 2622 cms flow in 1983: The peale of this flow was over twice that of the proposed test flow, <br />and riparian vegetation persisted during subsequent flows from 940 to 2: 1700 cms from 1984 <br />through 1986, and 1993. Although regrowth of vegetation was minimal during the high, and <br />often constant flood flows from 1983 to 1986, vegetation increased greatly following controlled <br />water years with interim flows beginning in 1990. Limited observations and aerial photography <br />of the 1275 cms flow in 1980 found that sand bars and wetland vegetation were not scoured by <br />that event. Marshes were severely scoured by the 1983 flood flow but recovered with interim <br />flows. As marshes that began as return current channels fill with sediment, they are colonized <br />by woody species and are no longer available as habitats for larval native fishes or as feeding <br />habitats for southwestern willow flycatcher. The objective, if possible, is to allow the river <br />ecosystem to go through this dynamic process and not be fixed in just one point in time. <br /> <br />3. Determine test flow velocities at nest sites in comparison with velocities that occurred during <br />the 1983 peale flow: Water velocities at several cross sections that represent the four primary <br />southwestern willow flycatcher territories in Grand Canyon were reviewed using a flow model <br />and water velocities measured by researchers as sites near territories. As anticipated, mainstem <br />velocities will be less during the 1275 cms flow than those of 1983 flood flows that exceeded <br />2400 cms. Mainstem velocities were predicted to range from 1.30 to 3.34 mlsecond (mfs) at <br /> <br />Biological and Conference Opinions Glen Canyon BcachlHabital-Building Rows 2/16196 <br /> <br />11 <br />-- <br />