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Geomopphology and Habitat Orchard and Schmidt (1998) found the character of eddy habitats to be strongly influenced by discharge, whereas the total amount of eddy area was not. Eddies increase in frequency and decrease in size as discharge increases from baseflow to about 7,OOG cfs. Above 7,000 cfs eddies became larger but less frequent, resulting in essentially no net change. At low discharges, the majority of the low-velocity habitat occurs as large eddies formed by channel ,~~ , constrictions. The-total length of inundated shorelines, the complexity of shoreline habitats, and the relative abundance of inundated vegetation, bare sand, and cobble bars along shorelines are all determined by discharge. Low discharges result in highly complex shoreline habitats with primarily bare sand and gravel substrates. The nursery habitat project focused on these shoreline habitats as flows decreased to base flows. This increase in shoreline complexity was more ~-_ thoroughly described by Day et al (1999) who sampled a total of 729 backwater and low velocity ''~~ flow habitats between June, 1994, and September, 1996. Numbers of backwaters sampled varied between years and seasons (see Report B; Table 2). The predominant backwater class found in ~ r Deso/Gray was shoreline eddy, i.e., sediments deposited in recirculating flows (backwater ~:. E ' formed as flows receded). This class accounted for 36.2% (n=264) of all sampled sites. Although shoreline eddy habitats were not significantly correlated with peak flow events, there F ~ ~t was a negative correlation (~==0.62) with flows during sampling periods. Green River fish habitat is complex and dependent on surrounding geology and variable flow regimes (Schmidt 1996). The following geomorphological tendencies were apparent. Eddy formed backwaters are the dominant backwater habitat available to YOY fish in these canyon reaches. The shoreline features that create eddy habitats are generally stable structures and usually persist through a runoff event. As result low velocity habitats during the baseflow period formed. in basically the same places from year to year. `"" In Deso/Gray, the area occupied by the active channel has decreased on average 19 ,~ ~, percent since the beginning of this century. Two episodes of channel narrowing were identified, '~ evidenced by two new and distinct surfaces that have formed this century. The cottonwood ~_-`~ terrace is an abandoned flood plain thaf began to stabilize between 1922 and 1936 as a result of naturally-occumng climate change. After the closure of Flaming Gorge Dam, a second lower l surface, the modern flood plain, has become densely colonized by riparian vegetation and is accumulating sediment by the process of vertical accretion. In reaches upstream and downstream from Deso/Gray, vertical accretion and channel simplification have caused the loss of secondary ~. j channels and the elimination of substantial habitat (Allred 1997, Graf 1978). Vertical accretion has caused the closure of one secondary channel in one of the Deso/Gray study reaches (see ~ photographic comparisons Report A; figures l la and 1lb). Secondary channels around several ~;~ other islands have been colonized with substantial vegetation which indicates the channels are being stabilized and abandoned. All of which lead Orchard and Schmidt to the conclusion that the process of channel narrowing observed between 1963 and 1993 has likely not abated. They further surmise that vegetation will continue to increase in density on low-elevation surfaces resulting in additional channel narrowing and the accompanying loss of habitat. '~ ` Because the historic channel was largely free of vegetation, the conditions observed today ~~~' . at baseflow -highly convoluted shorelines, abundant shoreline eddies, and unvegetated low level sand and cobble bars -would have persisted in the historic channel over a much wider range of ~ :`; •. ~ discharges. Increasing discharge now submerges bare sand and cobble bars and substantially t. x