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<br /> <br />WUA equate with some means of fish habitat or standing crop. <br /> <br /> <br />mendations. The decision~making process is clear and defensible and the me <br /> <br />is not burdened by unquantifiable assumptions such as that wetted perimeter <br /> <br />assumption is that the defined flow is as adequate for the rest <br /> <br />it is for the specified segment or habitat type. The user is further afforded <br /> <br />the flexibility to alter criteria for unique streams, species or life stages of <br /> <br />fish, or aquatic invertebrates. <br /> <br />Physical Habitat Simulation Models <br /> <br />None of the PHABSIM methods showed a sfgnificant lack of bias. Likewise, no <br /> <br />significant tendencies were noted. However, a closer analysis of IFG-4 results <br /> <br />revealed a distinct pattern when arranged by stream size (Table 6). From these <br /> <br />data, it appears that these methods tend to provide relatively high MF estimates <br /> <br />on small streams (<30 c fs AF) and relatively low MF es timates on larger streams <br /> <br />(> 1 00 c f s AF). <br /> <br />On smaller streams we surmise that WUA increases as the water surface eleva- <br /> <br />tion rises to and exceeds bank full. The possible reduction in WUA in the main <br />. <br /> <br />channel caused by increased velocities may, be outweighed ,by increases in WUA <br /> <br />along the stream edges, resulting in the high preferred flow estimate. <br /> <br />In larger streams, boundary-layer velocities (stream sides and bottom) may <br /> <br />be a more important habitat component for trout than mean column velocities. In <br /> <br />these streams, IFG-4 results show that higher flO\JS are detrimental due to <br /> <br />higher mean column velocities while in fact boundary layer velocities may be <br /> <br />within a preferred range. The model shows increased WUA at lower flows based on <br /> <br />12 <br />