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<br />co <br />c:..:> <br />~ additional information on changes that have occurred since closure of Navajo Dam. These additional <br />c.;) data from comparison of recent and historic aerial photography, plus results of surveys already <br />a completed, and final analysis of ongoing channel geometry studies should provide the information <br />to adequately meet this objective. <br /> <br />5.2.3. Quantify and Compare I Contrast Available Aquatic Habitats as a <br />Response(s) to Natural and Manipulated Flows. <br /> <br />5.2.3.1. <br /> <br />Monitor the Fate of Habitat Availability as a Result of Different Flows. <br /> <br />The effect of flow on habitat availability in the San Juan River has been addressed by several studies, <br />including Pucherelliand Goettlicher (1992), Goettlicher and Pucherelli (1994), Bliesner and Lamarra <br />(1994, 1995,1996), and Buntjer et al. (1994). <br /> <br />Pucherelli and Goettlicher (1992) used videography and Map and Image Processing System (MIPS) <br />to quantify secondary channel, backwater, and isolated pool habitats in the San Juan River during <br />1991. It was assumed that these habitats represented potentially important nursery areas for young- <br />of-the-year(YOY) and juvenile native fishes, particularly Colorado squawfish. The San Juan River <br />from Hogback Diversion (RM 158) to Mexican Hat (RM 52) was flown and videotaped on five <br />separate occasions to quantify habitats at a range of flows and at different times in the hydrograph <br />(e.g., on the ascending limb prior to peak flow, during peak flow, and on the descending limb <br />following peak flow). The range of flows videotaped in 1991 was 678 to 3,830 cubic feet per second <br />(cfs). Video images were then processed using a MIPS to determine the number and area of <br />secondary channels, backwaters, and isolated pools. <br /> <br />Results of the study showed a strong relationship between flow and backwater and secondary <br />channel habitat. Maximum backwater habitat occurred with flows in the range of 653 to 1,210 cfs. <br />Maximum secondary channel habitat occurred at higher flows, in the range of2,350 to 4,530 cfs. <br />An intermediate range of flows from 1,210 to 2,380 cfs maximized both habitat types. <br /> <br />,Videography recorded in 1991 revealed some morphologic differences among the various portions <br />of the study area. In RM 158 to RM 119, both secondary channel area and number decreased with <br />decreased flow. However, in RM 118 to RM 68, secondary channel area decreased with decreased <br />flow while the number of secondary channels remained relatively constant until flows dropped below <br />1,210 cfs. This suggested that morphology of the river channel between RM 118 and RM 68 is such <br />that the secondary channels can exist over a wider range of flows than in the area from RM 158 to <br />RM 119. <br /> <br />Backwater area generally exhibited increased area with decreased flow from RM 158 to RM 68. <br />However, backwater area was highest during peak flow from RM 118 to RM 68. This was <br />speculated to be due to a "high flow habitat zone," where backwaters formed only at higher flows <br />as water encroached into ephemeral tributary'stream channels. <br /> <br />Habitat to flow relationships indicated that the reach from RM 67 to RM 52 had a distinctly different <br />morphology than the area from RM 158 to RM 68. Both backwater and secondary channel habitat <br />were very limited in this reach (RM 67 to RM 52) until flows dropped to 1,200 cfs. At higher flows, <br /> <br />San Juan River Recovery Implementation Program <br />Summary Report <br /> <br />14 <br /> <br />17 January 1997 <br />PR-576-2 <br />