8137 - Laserfiche WebLink

Home Browse Search

SCALE 'N MILES -- ,,-=~ * RIVER MILE .5 SCALE IN M1LES 0=510 FIGURE 2. General and detailed location maps for the study reaches of the Yampa River, Colorado. tIe Snake River confluence to Echo Park at the Green River confluence, a distance of about 45 river miles. A multidisciplinary study of spawning- habitat formation for the Colorado squaw- fish was conducted by a team of biologists, hydrologists, geomorphologists, and en- gineers in July 1991 at two known Colo- rado squaw fish spawning sites at RM 16.5 (Cleopatra's Couch spawning bar) and RM 18.5 (Alternate spawning bar) on the Yam- pa River within Dinosaur National Mon- ument (Figure 2). Both spawning sites are coarse-grained midchannel bars that are located in bedrock-bounded canyon sec- tions of the river. Tyus (1992) has argued that identification of the requirements and needs of endangered fish species should be carried out in the least physicochemi- cally altered river systems, where it is as- sumed the fish occupy optimum habitat. The Yampa River fits these criteria both in terms of the minimal degree of flow pat- tern alteration (Tyus and Karp 1989) and the persistence of endangered species (Tyus and Karp 1989; Tyus 1990, 1992). Hydrology Correlation of the short period of Deer- lodge Park gage record with the longer period of Little Snake River at Lily and Yampa River at Maybell gage records en- abled a 70-yr record to be synthesized for the canyon section (Resource Consultants Inc., unpublished report). Average annual discharge is about 2,100 cfs, and the mean flow during the spring runoff (April-July) is about 5,400 cfs. Monthly base flow av- erages 500 cfs from August to March. The flood of record occurred in May 1984 and had a peak discharge of about 33,200 cfs. Analysis of daily flow data for the period of record enabled representative dry (1931, 1955, 1961),average(1941, 1951, 1956), and wet (1932, 1962, 1979) conditions to be identified. At Deerlodge Park, represen- tative peak daily flows for dry, average, and wet years are 7,000 cfs, 11,000 cfs, and 13,500 cfs. Sediment Supply Elliott et a!. (1984) concluded that the majority of the approximately 2 million tons per year of sediment transported through the Yampa Canyon was derived from upstream, and that the Little Snake River was a major source of sand. Wash load comprises about 35% of the total sed- iment load, and the effective discharge, de- fined as the increment of discharge that transports the largest fraction of the an- nual sediment load over a period of years, is about 10,100 cfs (Andrews 1978). Field observations within Yampa Canyon indi- cated that local tributary delivery to the Yampa River by summer thunderstorm- generated debris flows of very coarse cob- ble-to-boulder-sized sediment is important in forming local hydraulic contraction and expansion zones. Such zones have a marked effect on the locations of sediment-storage zones within the canyon. Locally derived sandstone 'and limestone clasts comprise the bulk of the coarsest sediments that form both midchannel and bank-attached bars within the reach (Berry 1985). Channel Morphology The upper 25 mi of the Yampa Canyon (RM 20-45) are bounded by the Morgan Formation, which is comprised of in- terbedded limestones, shales, and sand- stones (Steele et a!., unpublished report). The canyon is relatively wide and asym- I M. D. Harvey et a1. U711~