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<br />. <br /> <br />. <br /> <br />. <br /> <br />WUA Predictions <br /> <br />The calibrated data decks were run through the HABTAT4 program to develop WUA <br />versus discharge relationships for adult (size 5; 400+mm) and spawning life <br />stages of the Colorado squawfish, and the adult life stage of the humpback <br />chub (size 5;260+mm). The results suggest that adult Colorado squawfish <br />habitat is maximized at 100 cfs, with spawning habitat maximized at 1200 cfs, <br />and adult humpback chub habitat maximized at 400 cfs. <br /> <br />In comparison to the historic record of mean monthly flows for the Yampa River <br />from 1922 to 1986 (Attachment 2), 100 cfs is exceeded 100.0 percent of the <br />time in June, 98.5 percent in July, 95.0 percent in August, and 84.6 percent <br />of the time in September. Similarly, 1200 cfs is exceeded 98.0, 60.0, and 3.1 <br />percent of the time in June, July, and August respectively; deposition does <br />not occur in September. 400 cfs is exceeded 100.0, 87.7, 46.2 and 23.1 <br />percent of the time in June, July, AU9ust and September. The models' <br />predicted optimal flows for adult Colorado squawfish and humpback chub <br />habitats are rare historic events, and probably do not represent optimum <br />biological conditions. <br /> <br />The adult squawfish SI curves used in this analysis are applicable only for <br />the months of July, August and September. Similar to the Spawning Bar, model <br />outputs suggest adult habitats are optimal at flows close or equal to zero <br />(Attachement 1; SI curve velocity coordinates). The adult humpback chub <br />curves are applicable from March to November. The WUA versus flow <br />relationship peaks at 400 cfs, with a gradual decline above 1500 cfs. The <br />depth and velocity SI curves for humpback chub peak at 7.0 feet and 0.23 <br />ft/sec, respectively. <br /> <br />The deposition curves are useable throughout the spawning period, generally <br />June, July, and August. The deposition velocity curve peaks at 2.27 ft/sec, <br />while the depth curve peaks at 2.04 feet. The prediction of WUA for <br />deposition habitat which peaks at 1200 cfs (Table 8), more accurately reflects <br />historic flow conditions~ <br /> <br />3. MAYBELL <br /> <br />The Maybell study site, located at RM 72.0, was surveyed and described by Mike <br />Prewitt in 1979 using the three-flow IFG4 model. Wahle made a few minor <br />changes to the original data, recalibrated the deck and reran the model <br />through the HABTAT program. Similar to the Spawning Bar and Replicate sites, <br />the data deck used in this analysis retained the corrected stage-of-zero flow <br />values, the compatible substrate code, and water surface elevations. The <br />Maybell data deck modifications are comparable to those in the Spawning Bar <br />and Replicate data decks, and therefore are not included in a separate table. <br /> <br />The geomorphic stability of this area was evaluated by Wahle and Johnson <br />(1984). The analysis utilized aerial photographs to evaluate the channel <br />morphology. From the photographs, channel substrate formations indicated a <br />stable gravel/cobble/rock combination with relatively little sand (Wahle and <br />Johnson 1984). The area was considered to be in dynamic equilibrium. <br /> <br />In <br />'V <br />