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<br />I <br />I <br />I <br />I <br />1\ <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />earlier warming when compared to the Colorado River (Figure 12). The Colorado River generally <br />reached comparable temperatures 10 to 20 days after the Dolores River. Temperatures in the <br />Dolores were consistently higher than in the Colorado River except during November - January. The <br />effect of differences in warming of the Colorado and Dolores rivers on migration and spawning cues <br />of Colorado squawfIsh is unknown. <br /> <br />RM 64.5-177.0. Temperatures in this reach ranged from 0 to 30 oC, with highs occurring in July <br />and August and lows in winter months. Releases from McPhee Dam had a profound effect on <br />temperatures in this region. Effects were seen in both diel and annual temperature patterns. Diel <br />temperature patterns were primarily affected by low volume releases during summer months. During <br />this time, diel temperature swings were extreme because of the small thermal mass in stream flow. <br />This problem was particularly acute in low velocity habitats such as pools and backwaters where warm <br />temperatures were often accompanied by depressed oxygen levels. From April through July, 1991, <br />the monthly extreme diel temperature ranges in the mainstem Dolores River, just above the San <br />Miguel River confluence, were 3.2-8.9, 5.9-12.3, 13.6-19.4, and 13.9-20.10C, respectively (T. Beck, <br />CDOW, unpublished data). <br /> <br />Changes to annual temperature patterns related to the operation of McPhee Dam were <br />potentially deleterious to native species. Premature warming during low flows in April and May <br />initiated gonadal maturation and spawning by native fish species including roundtail chub, <br />flannelmouth sucker and bluehead sucker. Warm temperatures followed by cold releases probably <br />killed large numbers of eggs and larvae. Data provided by CDOW indicate that water temperatures <br />during low flows (20 cfs) in 1990 reached 160C by mid April and 180C by the first week in May. <br />Large aggregations of flannelmouth suckers were observed during the same time period in the upper <br />Dolores River and individuals showing signs of spawning readiness were captured (T. Beck CDOW, <br />pers. comm.). <br /> <br />A distinct temperature break occurred at the confluence of Disappointment Creek (RM 128.7). <br />Above this point, under normal flow conditions, the Dolores River was relatively cooL The river <br />flowed through extensive canyon areas which delayed warming. Below Disappointment Creek the <br />channel became more open and the river warmed as it traversed a broad flood plain. During the <br />summer, main channel temperatures above and below Disappointment Creek differed by as much as <br />40C and turbidity increased significantly below (Beck 1989). Higher turbidity below Disappointment <br />Creek was the result of highly erodible shales and sandstones. Disappointment Creek represented <br />a distinct geomorphic transition in the Dolores River system where the river changed from a cool, <br />clear stream to a warm, turbid system. <br /> <br />4.3.1.3 Habitat Availability/Channel MoroholO2V. A general description of channel morphology <br />and gross habitat structure of the Dolores River was presented by Valdez et a1. (1982). This <br />description included maximum and average depths, channel width and a description of floodplain and <br />channel characteristics. The present study indicated that few changes in gross physical habitat <br />occurred in the Dolores River since 1981, except for sedimentation. Observations and <br />communications (Personal communication with T. Beck, CDOW) indicate that fine sediments <br />accumulated in the Dolores River channeL This problem was most acute above the confluence of <br />the San Miguel River where McPhee Dam greatly reduced or eliminated spring runoff flushing flows. <br />Below the confluence of the San Miguel River, sediment was less evident. Additional studies would <br />be required to evaluate sedimentation and channel armoring. A description of habitat and channel <br />morphology for each reach of the study area is presented below. <br /> <br />13 <br />