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<br />11 <br /> <br /> <br /> <br /> <br />t <br />lout-velocity winter habitats are losing effective depth and being invaded by <br />flawing water. Bed changes can also occur as sediments are moved by shifting <br />currents (Figure 19a-g). Fish could be trapped or crushed during this critical <br />time. We noticed that fish appeared to move around more at this time, perhaps <br />as a response to ice-out conditions. <br />Ice-out can be a violent event. Temporary ice jams can quickly raise <br />water levels several feet. When these jams break up, high flows can sweep <br />throe areas changing channel beds. Large slabs of ice tilt up on end and <br />scrape along the river bottom. Severity of ice-out conditions varies <br />considerably between river reaches. Immediately after ice-out in Winter 1, <br />dramatic channel bed changes occurred at the backwater at RMI 95.7. Large <br />amounts of gravel were pushed into the upper end of the backwater, and large <br />pieces of ice were deposited over the gravel bar. All three of the fish that <br />used this backwater during the Winter were located downstream after ice-out. <br />However, at the embayment at RMI 81.1 little change was noted and very little <br />ice was deposited in the area. Radiatagged fish remained in the embayment <br />area during ice off. <br />Stage vs discharg predictions with ice over <br />t <br /> <br /> <br /> <br /> <br /> <br />Regression analysis was performed on stage (water surface - zero flow <br />elevation) and discharge data according to methods outlined by Bovee and <br />Milhous (1978). Comparisons were made of regressions using two sets of data. <br />Values for the coldest portion of the winter from mid-December until mid- <br />February (Figure 20) were compared to the data set including the Warmer, high- <br />discharge period of early March (Figure 21). <br />Preliminary results using both data sets indicate that the expected loss <br />in stage elevation at RMI 81.1 would be about 0.2 feet for every 20 cfs <br />reduction in discharge (Tables 14 and 15). If discharge were reduced from the <br />lowest wed flow of 142 cfs to 75 cfs, about 0.7-foot reduction of stag <br />elevation would occur. These predictions are based on measurements of the <br />water surface elevation that would occur at zero flaw, which would amount to a <br />reduction of stag elevation of 1.54 feet. These relationships are specific <br />to the hydraulic conditions that exist at RMI 81.1. Flow reductions in other <br />river segments could result in different stage elevation changes. As a <br />general rule wider river reaches would have smaller elevation changes than <br />narrow river segments. <br />A=1cability of PHABSIM <br />At the inception of this project, it was assumed that the Instream Flow <br />Incremental Methodology (IFIM) (Bovee 1981) and Physical Habitat Simulation <br />(PHAB.SIM)'(Milhous et al. 1984) model would be used to determine suitable <br />' winter flow regimes. It became apparent that this approach would not be <br />appropriate after observing fish behavior patterns and the complications of <br />ice effect. Since no standardized or proven method for determining adequate <br />' winter flows were available, methods used in this report were developed based <br />on recxx ,-cations from professional biologists and hydrologists. <br />Assumptions of the PHABSIM methodology were outlined by Orth (1982): (1) <br />depth, velocity, and substrate are the most important habitat variables <br />affecting fish distribution and abundance when changes in flow regime are <br />considered; (2) the stream channel is not altered by changes in flaw regime; <br /> <br />53 <br />1