San Juan River Recovery Implementation Program Summary Report 1991-97

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Reach 5 (RM 131 -154) below the "Mixer" to above Shiprock, New Me xico. Valley width in Reach 5 is greatest of all eight geomorphic reaches. Channel gradient (0.00193 ft/ft) and sinuosity are intermediate between the two adjacent reaches, both increasing in an upstream direction. Total water surface area is relatively large in this reach at most flow levels (largest at high flows) as a result of a broad, shallow main channel and extensive overbank flooding at high flows. Island area is largest in this reach at all flow levels, indicating extensive secondary channels. Many of the islands in this reach are very well vegetated with Russian olive, tamarisk, and remnant cottonwood stands and are relatively stable compared to islands in other reaches. Total amount of low velocity habitat in this reach is probably greater than in most lower reaches, although density of low velocity habitat may be higher in isolated areas of other reaches, particularly Reach 8. Cobble and mixed substrates are prevalent in the reach. This reach contains "the Mixer" (RM 129.8- 133.4), an extensively braided section of river. Reach 5 includes the municipality of Shiprock, New Mexico, and is substantially affected by human activity, including a large increase in irrigated land adjacent to the river and the presence of a major diversion structure (Cudei Diversion). One perennial tributary, the Chaco River, and two major ephemeral tributaries enter the river in this reach. Related Biological Information: Two suspected spawning areas for Colorado squawfish are located in the Mixer portion of Reach 5, based on aggregations of radio - tagged adults during the spawning period during two consecutive years (Miller 1994a, 1995). One spawning area is at RM 131.1 and the other is just upstream at RM 132. Both of these areas appear to provide a large diversity of habitats, interspersed among small islands and cobble bars, that provide areas suitable for both resting and spawning. Year -round use of the reach by radio- tagged adults and the substantial number of captures of adult Colorado squawfish throughout the reach suggest its importance as year - round habitat for the species. Cudei Diversion, located in Reach 5 at RM 142, represents the approximate upstream distributional limit of Colorado squawfish in the San Juan River at the present time. Only one radio - tagged adult has been observed temporarily above the diversion. Roundtail chub have also been found relatively frequently in this reach. Reach 6 (RM 155 -180) Shiprock New Mexico, to Just below the Confluence o the Animas River. Valley width in Reach 6 decreases slightly from Reach 5, but is still second greatest of all reaches. Average channel gradient (0.00209 ft/ft) and sinuosity in the reach are also second highest of all reaches. The amount of island area in this reach is substantially less than in Reach 5, indicating less extensive secondary channel development. Cobble substrate is prevalent in the reach. The reach includes the municipalities of Fruitland, Kirkland, and Farmington, New Mexico, and may be the most affected by human activity, with irrigated land adjacent to 100 percent.-of-the- -river and four major diversion dams located within the reach (see Figure 1). Three perennial tributaries enter the San Juan River in this reach, the La Plata River, Ojo Amarillo Canyon, and the Animas River. Ojo Amarillo Canyon, historically an ephemeral wash, is now perennial in character primarily due to irrigation return flows from relatively recent agricultural development in the area. I San Juan River Recovery Implementation Program December 1997 Summary Report 9 PR -602 -1