Laserfiche WebLink
<br />/';}oo, <br />';'-./ <br /> <br />,';c.. <br />~.I <br /> <br />". <br /> <br />correlated with the presence of Cladophora and therefore declines with distance from the dam. <br />Because Cladophora serves as a substrate for epiphytic diatoms which composes the major <br />portion of the diet of the aquatic chironomid dipterans, and the introduced, non-indigenous <br />arnphipod. Gammarus lacustris, populations oftbese taxa have increased in the aquatic <br />environment of the Canyon following closure of the dam. <br />Changes in physical characteristics of the river have also altered the fish assemblage. <br />The clear, cold tailwater between the dam and Paria River, and establishment of a productive <br />food base in this reach, have permitted development of a population of non-idigenous trout, <br />managed to maintain a recreational fishery. Cold water, coupled with existence of an exotic <br />predatory fish have led to essential extirpation of the original eight indigenous Colorado River <br />fish species between Glen Canyon Dam and Lake Mead (Minckley 1991). Of the original <br />indigenous species, humpback chub, bonytail. Colorado River squawfish and razorback sucker <br />are listed as endangered (bonytail and squawfish are locally extirpated), while speckled dace, <br />flannelmouth sucker, and bluehead sucker remain relatively common. Of the endangered fishes, <br />only humpback chub maintains a reproducing population, an apparent result of its use of the <br />Little Colorado River as a refuge and spawning site. <br />Studies during Phases I and II of the Glen Canyon Environmental Studies have <br />demonstrated that geomorphological changes in concert with hydrological changes and <br />alteration of water physical features (e.g., temperature and sediment transport) have altered <br />many of the ecological processes within the Colorado River riverine system below Glen Canyon <br />Dam. Periodic reestablishment of the geomorphic and hydraulic proce;ses that may enhance <br />rnaintiinence of ecological processes and communities without creating negative effects on <br />existing biota, especially indigenus species, should be another of the major objectives of flood <br />mllnllgement, in addition to sand transfer from channel bed to banks. <br /> <br />EXPERIMENTAL DESIGN <br /> <br />GEOMORPHOLOGY <br /> <br />Obiectives <br />The objectives of this part of the study are to validate predictions of (I) locations and <br />rates of sand deposition along margins oftbe channel, (2) locations and magnitude ofnet <br />. erosion, and (3) characteristics ofwater and sediment transport in the main channel, and eddies <br />and return current channels. Measurements will focus on quantification of the rates of <br />geomorphic pr~se;, descriptions of these processes, mapping of existing deposits, and <br />measurements of flood-formed deposits. Measurements will also be made of the rate of <br />post-flood adjustment of newly formed deposits. <br /> <br />J ustificatiOD <br />As described above, use of intentional floods as a tool in habitat reconstruction depends <br />on (I) accurate understanding of the sediment budget, (2) ability to predict reach-averaged rates <br />of channel-margin deposition, and (3) determination of variance of the spatial pattern of reach <br /> <br />10 <br />