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amount of low velocity habitat is high in the reach, particularly near the dam, and is probably related <br />to substantial channel alterations in the area and to the low gradient. Cobble substrate is prevalent, <br />and pool habitat is more abundant in Reach 8 than in any other reach. The municipality of <br />Archuleta, New Mexico, is located within the reach and approximately 30 percent of land adjacent <br />to the river channel is irrigated. This is substantially less than in Reach 7. One diversion dam is <br />also located within the reach. <br />Related Biological Information: Biological characteristics of Reach 8 are dictated by the operation <br />of Navajo Dam and represent a cold tailwater situation. Cold water temperatures, the absence of <br />suspended sediments, and a highly - altered hydrograph provide good habitat for trout. This area is <br />a very important recreational coldwater fishery in the region. Primary and secondary production in <br />this reach may provide an important source of energy to downstream reaches. <br />Summary <br />Eight distinct geomorphic reaches were identified in 1995 following 3 years of investigation and <br />analysis of an array of physical factors in the San Juan River between Navajo Dam and Lake Powell <br />(Bliesner and Lamarra 1995). Identification of these reaches effectively addressed Objective 5.2.1.1 <br />of the LRP and provides the basis to evaluate relationships between geomorphic and biologic <br />phenomena in the San Juan River below Navajo Dam. In addition, ongoing studies reported by <br />Bliesner and Lamarra (1996) continue to evaluate differences in various physical and biological <br />factors such as substrate embeddedness, biomass, and backwater productivity among the eight <br />geomorphic reaches. <br />5.2.1.2. Characterize Habitat for Each of the Reaches. <br />Contributing Investigations <br />Information on habitat characteristics associated with the eight geomorphic reaches identified in the <br />San Juan River below Navajo Dam have been presented by Bliesner and Lamarra (1993, 1994, 1995, <br />1996). <br />Findings <br />Data collected on macrohabitat availability in 1994 through 1996 indicated that run habitat is <br />predominant in all geomorphic reaches and is relatively constant, as a percent of total wetted <br />perimeter, among reaches. However, some habitat types appeared to vary among reaches. For <br />example, in 1995 shoal habitat decreased from 20 percent of total to 2 percent of total from Reach <br />2 to Reach 1, while low velocity habitats, which were relatively constant at 1 to 2 percent of total <br />in the lower four reaches, varied widely among the upper four reaches (Bliesner and Lamarra 1996). <br />Backwater habitat quality surveys suggest some trends in backwater quality across geomorphic <br />reaches. For example, backwater temperatures were highest in Reach 5 and dropped off in <br />downstream reaches, particularly in canyon -bound reaches like Reach 1 and 2, where shading may <br />affect water temperatures. Backwater volume also exhibited trends that appear to be correlated with <br />channel gradient. Backwater volume was generally highest in the lower two reaches and Reach 8 <br />(the uppermost reach) where channel gradient was generally lower (Bliesner and Lamarra 1996). <br />San Juan River Recovery Implementation Program December 1997 <br />Summary Report 11 PR -602 -1 <br />