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the same location. The HEC-2 model provided an extensive database on the <br />relationship of water depth versus flow at numerous other locations in the reach <br />than those conducted by FWS. Corroboration between the two methods increased the <br />available data base that could be used to make general conclusions about <br />relationships between stage and water depth over a wide range of flows in the <br />reach. No water depth data were collected on the relationship of low flow and <br />Colorado squawfish use in 1995 because flows in the Gunnison River were much <br />higher throughout 1995 compared to 1994 (Figure 1). <br />These results found that increasing flow does not translate to a <br />proportional increase in water depth. Although the general habitat is distinctly <br />dissimilar between the 2.3-mile reach of the Lower Gunnison River and the 15-mile <br />reach of the Upper Colorado River, Osmundson et al. (1995) noted similar <br />observations regarding availability of preferred habitats and flow. <br />Habitat-use and water depth-preference data for sub-adult and adult <br />squawfish that had occupied the 2.3-mile reach were not collected in this study. <br />However, general statements could be made about habitats and water depths <br />Colorado squawfish might prefer and need during summer low months in the 2.3-mile <br />reach of the Lower Gunnison River using Colorado squawfish data from the 15-mile <br />reach. Osmundson et al. (1995) found that during low summer flows in the 15-mile <br />reach, Colorado squawfish preferred slow and fast runs. During summer low-flow <br />months, they also reported that sub-adult and adult Colorado squawfish used slow <br />runs with water depths of 1.4-7.6 ft (mean=3.6 ft) and fast runs 1.8-3.0 ft deep <br />(mean=2.4 ft). The minimum water depth used by Colorado squawfish in the 15-mile <br />reach meant that 550 cfs would be required in the 2.3-mile reach of the Lower <br />Gunnison River to produce minimum depths of 1.4 ft at transects 9 and 19. <br />Although it is acknowledged that these two stream reaches are different in <br />habitat diversity and stream gradient, applying the water depth criteria for <br />Colorado squawfish in the 15-mile reach to the 2.3-mile reach provides a <br />reasonable estimate of minimum depth needed by Colorado squawfish. Furthermore, <br />the water depths recorded from radiotagged Colorado squawfish in the 15-mile <br />reach represent depth in preferred habitats and the corresponding flows <br />recommended for that reach are intended to optimize habitat and to promote <br />recovery. Therefore, recovery flows recommended for the 15-mile reach might be <br />higher than needed to provide passage in the 2.3-mile reach. <br />Flow Exceedence <br />Snow pack and moisture content data allow water managers to predict whether <br />a water year will be wet, above or below normal, or dry. Although flow duration <br />curves do not provide. water managers the ability to predict when low-flow <br />conditions will occur, they do provide them with some probability of how frequent <br />flows of interest may occur. A flow-duration curve predicts the likelihood of <br />various flows based on regional climatological conditions (i.e. annual snow pack) <br />and the amount of water available in the drainage based on current water <br />management practices. <br />Flow exceedence for three water development periods, 1917-1938 (pre-), <br />1939-1964 (mid-), and 1967-1994 (post-Aspinall), in the Gunnison River drainage <br />was analyzed. The mean daily flow exceedence for each month was computed for <br />27