San Juan River Recovery Implementation Program Summary Report 1991-97

Home Browse Search

reducing the numbers of fish participating in yearly spawning migrations into the river (Ryden and Ahlm 1996). The effects of the inundation of this fish barrier are being evaluated by ongoing investigations. Reach 2 (RM 17 -67) near Slickhorn Canyon to near Confluence with Chine Cree Reach 2 is also canyon- bound, with the narrowest valley width of all eight geomorphic reaches. Sinuosity of the channel is as low as in Reach 1 (RM 0 -16) due to canyon confinement, but the channel gradient is significantly higher than both adjacent reaches (0.00178 ft/ft). Riffles comprise a large proportion of the surface habitat, and most of the major rapids in the study area are found in this reach. High water velocities and a relatively deep main channel are reflected in the low total water surface area observed in this reach over a wide range of flows. Cobble substrates are more prevalent in this reach than in Reach 1 but less prevalent than in Reach 3. A series of bedrock and talus control points increase channel complexity in localized areas within this reach. Reach 2 includes the municipality of Mexican Hat, Utah, and an increased amount of human activity adjacent to the channel relative to Reach 1. Related Biological Information: Six YOY Colorado squawfish and three YOY roundtail chub have been captured in this reach, indicating that this reach provides some nursery habitat for rare species in the system. The presence of these fish is probably also related to the reach's downstream juxtaposition relative to suspected spawning areas for both Colorado squawfish and roundtail chub. Five of 16 radio - tagged razorback - sucker that were stocked into upstream portions of the San Juan River in the fall of 1994 used this river reach for a substantial period of time. Although many factors probably affected the movements of these stocked fish, use of Reach 2 may indicate its suitability for adult razorback sucker. Ongoing investigations of movements and habitat use of the San Juan River by stocked razorback sucker should provide the data to more fully evaluate the potential importance of this river reach. Reach 3 (RM 68 -105) near Confluence of Chinle Creek to Just Upstream of An eth, Utah. The river flows through a moderately broad valley in this reach. It has a more sinuous channel than either Reach 1 or 2. Channel gradient is significantly lower than in both adjacent reaches and is second lowest of all reaches (0.00143 ft/ft). Cobble substrates are also more prevalent in Reach 3 than in the lower reaches; however, they are interspersed with a series of large, sand shoal complexes associated with areas of channel instability. This area of sand shoal complexes, termed the "debris field," appears to be associated with the effects of a series of cobble areas acting as channel controls. One of the largest of these cobble deposits is located at the entrance to a canyon at the beginning of Reach 2. It is speculated that the abrupt narrowing of the valley as it enters the canyon acted as a control point during large magnitude flow events during the last 5,000 to 10,000 years, resulting in this large cobble deposit just upstream of the canyon mouth. This restriction, in combination with the sediment input of several high - gradient tributaries with erodible watersheds ( Chinle Creek, Combs Wash, Cottonwood Wash, and Monument Creek), created the conditions partly responsible for the channel morphology presently seen in this reach (V. Lamarra 1997, pers. comm.). Secondary channels also become more prevalent in this reach compared to Reach 1 or 2. Reach 3 includes the municipalities of Bluff and Aneth, Utah, and a corresponding increase in human activity adjacent to the channel relative to Reach 1 or 2, including the presence of some irrigated agricultural areas San Juan River Recovery Implementation Program December 1997 Summary Report 7 PR -602 -1