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<br />Reach 4 (RM 107 to 130, Aneth, Utah, to below "the Mixer") is a transitional reach between the
<br />upper cobble-dominated reaches and the lower sand-dominated reaches. Sinuosity is moderate
<br />compared with other reaches, as is gradient. Island area is higher than in Reach 3 but lower than
<br />in Reach 5, and the valley is narrower than in either adjacent reach. Backwater habitat
<br />abundance is low overall in this reach (third lowest among reaches) and there is little clean
<br />cobble.
<br />Reach 5 (RM 13 I to 154, the Mixer to just below the Hogback Diversion) is predominantly
<br />multi-channeled with the largest total wetted area (TW A) and largest secondary channel area of
<br />any of the reaches. Secondary channels tend to be longer and more stable than in Reach 3, but
<br />fewer in number overall, Riparian vegetation is more dense in this reach than in lower reaches
<br />but less dense than in upper reaches. Cobble and gravel are more common in channel banks than
<br />sand, and clean cobble areas are more abundant than in lower reaches, This is the lowermost
<br />reach containing a diversion dam (Cudei). Backwaters and spawning bars in this reach are much
<br />less subject to perturbation during summer and fall storm events than the lower reaches.
<br />
<br />Reach 6 (RM 155 to 180, below the Hogback Diversion to confluence with the Animas River) is
<br />predominately a single channel, with 50% fewer secondary channels than Reaches 3, 4, or 5.
<br />Cobble and gravel substrates dominate, and cobble bars with clean interstitial space are more
<br />abundant in this reach than in any other. There are four diversion dams that may impede fish
<br />passage in this reach. Backwater habitat abundance is low in this reach, with only Reach 2
<br />having less. The channel has been altered by dike construction in several area to control lateral
<br />channel movement and over-bank flow.
<br />
<br />Reach 7 (RM 181 to 213, Animas River confluence to between Blanco and Archuleta, New
<br />Mexico) is similar to Reach 6 in terms of channel morphology. The river channel is very stable,
<br />consisting primarily of embedded cobble substrate as a result of controlled releases from Navajo
<br />Dam. In addition, much of the river bank has been stabilized and/or diked to control lateral
<br />movement of the channel and over-bank flow. Water temperature is influenced by the
<br />hypolimnetic release from Navajo Dam and is colder during the summer and warmer in the
<br />winter than the river below the Aninlas confluence,
<br />
<br />Reach 8 (RM 2 I 3 to 224, between Blanco and Archuleta and Navajo Dam) is the most directly
<br />influenced by Navajo Dam, which is situated at its uppermost end (RM 224). This reach is
<br />predominantly a single channel, with only four to eight secondary channels, depending on the
<br />flow. Cobble is the dominant substrate type, and because lateral channel movement is less
<br />confined in this reach, some loose, clean cobble sources are available from channel banks. In the
<br />upper end of the reach, just below Navajo Dam, the channel has been heavily modified by
<br />excavation of material used in dam construction In addition, the upper 10 kID of this reach above
<br />Gubemador Canyon are essentially sediment free, resulting in the clearest water of any reach.
<br />Because of Navajo Dam, this area experiences much colder summer and warmer winter
<br />temperatures. These cool, clear water conditions have allowed development of an intensively
<br />managed blue-ribbon trout fishery to the exclusion of the native species in the uppermost portion
<br />of the reach.
<br />
<br />San Juan Rive, Non-native Species lnter.crions, Final Report, \ February 2000
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