WSP11633 - Laserfiche WebLink

Home Browse Search

14 CLARKSON ET AL. temperature, oxygen, or salinity levels where isolated pooIs persist. Some of these energetic effects also may be imposed upon older fishes that inhabit larger habitats such as tributary mouths, eddies, runs and riffles. Emplacement of Glen Canyon DamgreatIy curtaiIed sediment input from the Upper Colorado River Basin. The remaining sediment load reaching Grand Canyon, a loss of approximately 77%, or 66 million tons per year at Phantom Ranch (Andrews 1991), is essentialIy accounted for by tributary inputs below the dam (Figure 4). The 25 Ian reach between the dam and Paria River almost never receives sediment input, and a net loss of fine-grained materials from that area has resulted in substrate armoring (pemberton 1976, Howard and Dolan 1981, Kondolfet 8I.1989,Angradi et aI. 1992). Concern for a net Ioss of sediment over time in Glen and Grand canyons has been expressed (Dolan et al. 1974). , Altered post-dam hydroIogy and sediment transport dictate that geomorphological adjustments . in the river channel are inevitabIe (LeopoId et aI. 1964, Dawdy 1991). High water terrace depOsits are no longer inundated and are now being modified by vegetation and eolian changes (Turner and Karpiscak 1980, Howard and DoIan 1981). Flushing of fines from and conimiitution of large particles within high gradient reaches (especially rapids) is now less freci.iJent due to reduced flood magnitudes (Howard and DoIan 1981, Kieffer 1985, O'Brien 1987). Variable (aggradation and erosion) reach-wide and site-specific changes to fine- grained streambed and bank deposits have occurred due to interactions among patterns of Water'discharge, rate of stage change, and antecedent sediment storage conditions (Howard and"Dolan 1981, Beus and Avery 1993). - , . ;.,.~,...,I.'",~ Islands; sand bars, and beaches that are no longer scoured by spring high flows have been ii1Wded bi exotic salteedar' (Tdindrii chi1ieri.ds)'(Tufnerand KaipisCak 1980)':, This species has'trapped and stabilized sediment, causing an average reduction in channel width of 27% in the Green River in and near Canyonlands National Park, Utah (Graf 1978; but see Everitt 1979). This reduction of transportable sediments and expansion of stable deposits has decreased the ability of the channel there to adjust to substantial fluctuations in discharge (G~J978). - . ~'P.{;~~~H; ....., ,,'" Seasonal variations in water temperatUre practicalIy ceased following releases from Lake PoweiJ. through hypolimnial peristocks:. Mainchannel temperatures are now seasonally and pCreimiany cold, rarely ranging beyond limits of 7-15 C (Figure 4). Peripheral backwater liabifats partially isolated from mainchannelflows are one of the few habitats that warm . abOve these levels, but only seasonally during diel cycles and as a result of the combined effects" of stage fluctuations and levels of incident solar insolation (Maddux et al. _1987, ,K~biy 1990, Angradi et al: 1992). Effects C?f lowered temperatures on native Grand Canyon fishes include reduced growth rates and m~lism (Lupher and Clarkson 1994); decreased .