San Juan River Recovery Implementation Program Summary Report 1991-97

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Related Biological Information: Although not currently used by wild endangered fish species, physical habitat provided by Reach 6 appears to be suitable for Colorado squawfish and provides the best potential for expanding the range of the species in the San Juan River System. The reach is used by other native species (e.g., flannelmouth sucker, bluehead sucker, and speckled dace). Primary and secondary production from large riffle areas within this reach may represent an important source of energy for the native fish community in downstream reaches (Bliesner and Lamarra 1995). Several areas in this reach also appear to exhibit suitable physical characteristics for Colorado squawfish spawning habitat. If these spawning areas were used, backwater nursery habitat available to drifting larvae would be increased by approximately 34 percent over that which is available below existing spawning sites. In September 1997, 49 adult Colorado squawfish and 2,885 subadult razorback suckers were stocked into this reach. Four major diversion structures located in the reach represent potential barriers to the movement of Colorado squawfish and other native species, and may be one reason that the reach is not used by the Colorado squawfish. Irrigation and cooling plant withdrawals associated with these diversions also represent a potential source of mortality for native fish in the system since the younger life stages could become entrained in withdrawal structures while drifting downstream. W Reach 7 (RM 181-2 below Confluence of Animas River to between Blanco and Archuleta. Reach 7 is characterized by a wide valley, with a similar width dimension to Reach 6. Channel gradient is greater in this reach than all other reaches (0.00213 ft/ft) and sinuosity is similar to Reaches 5 and 6 but substantially less than Reach 8. Reach 7 has less total water surface than Reach 6, reflecting the reduction in flow above the confluence with the Animas River and the resulting narrower channel compared to the downstream reaches. The amount of island area in this reach is similar to the adjacent reaches, and the islands are generally stable relative to those in most other reaches. Runs are the prevalent habitat in Reach 7. The municipalities of Bloomfield and Blanco, New Mexico, are located within the reach. Irrigated land is adjacent to 100 percent of the river channel and the Hammond Diversion Dam is located within the reach (Figure 1). Water temperatures in this reach are transitional between the cold temperatures in Reach 8 and the warmer temperatures in Reach 6. Water clarity is also relatively high in this reach compared to those downstream, except when rainfall events cause Canyon Largo to flow. Gallegos Canyon, once ephemeral but now perennial due to irrigation return flows, enters the river in this reach. Related Biological Information: Proximity of Reach 7 to Navajo Dam substantially influences both its physical and biological characteristics. Physical parameters affected include water temperature, substrate characteristics, suspended sediments (water clarity), and discharge. Biologically, fauna and flora assemblages in the reach are more characteristic of a coldwater situation. The reach, particularly in the lower end, provides habitat for native species (e.g., flannelmouth sucker, bluehead sucker, and mottled sculpin). The upper portion of the reach is dominated by rainbow and brown trout. Primary and secondary production within extensive riffle areas in this reach may provide an important energy source for downstream reaches. Reach 8 (RM 214-224) between Blanco and Archuleta to Navaio D am. Valley width in Reach 8 is substantially narrower than in Reach 7. Channel gradient (0.00160 ft/ft) is also less than Reach 7. Sinuosity in this reach is greater than all other reaches. Density and San Juan River Recovery Implementation Program December 1997 Summary Report 10 PR -602 -1