WSP11654 - Laserfiche WebLink

Home Browse Search

scour) deep and shallow riffles (gravel, cobble and boulder) ; glides and rapids, Habitat units were visually identified and estimated, and later characterized based on depth and velocity measurements, Class I pools were defined as those over 2 meters deep with a velocity of less than 0,6 ft/sec and Class II pools were over 1 meter deep, These pools are consider good fall/winter habitat for adult squawfish and comparisons will be made between here and the Yampa River to estimate pool availability, Initial findings indicate that pools, compared to other habitats, are rare. Only 76 pools were found in 43 miles of river, comprising only 1.4 %- of the surface 'area. Glides is the unit used to describe the habitat intermediate between pools and riffles. Glides were typically 3 to 12 feet deep and had a velocity range of 1 to 3 feet/see, Glides were the most common habitat type (59,6 %-) in this section of the Colorado River. Cobble riffles (low gradient) riffles comprised 34.6%- with boulder riffles (high gradientland rapids comprising 4.0 and O,S%-, r~spectively. Complex channels, formed by islands or bars, were also enumerated during the fall habitat surveys, .. In November about 60%- of the river between Rifle and plateau Creek flowed in a single main channel. Therefore about 40%- of the river in this reach contained instream islands or bars. It did not appear that habitat diversity was increased in sections of the river that had just two branches, In general habitat diversity appeared higher in areas with complex channels of three or more river branches, and these were found to comprise 11.5%- of the river, The. channel was characterized into three categories based on its ability to overflow its banks, The ability to flood, or to' cut and erode banks is presumed to have been a common natural occurrence that resulted in the habitat diversity in which native fish evolved. It is further assumed that it is very undesirable for banks to become stabilized to the point that the channel can no longer naturally migrate, because losses of nursery habitat for native species appears associated with the river losing access to the floodplain, Fifty-seven percent of this river reach was considered confined (channelized) by high banks or rip-rap, About 29%- of the river would inundate vegetated perimeter areas on bars, islands or the shoreline, but would not inundate out of channel areas. Areas that appeared to have potential for flooding bottomlands were nearly always associated with side channels, and this was about 14%- of areas adjacent to the river . To further assist in the evaluation of channel condition, observations of natural features (side channels, backwaters, bars, beaver dams, cottonwood groves, LOD or fallen trees, and eroding banks) and unnatural features (jetties, revetments, dikes, diversion dams, gravel pits, salt cedar, Russian olives, bank rip rap from railroad or highway) were made. For example, salt cedar and Russian olive are common throughout 5