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<br />'. ~ 7.- <br /> <br />. ."-'-':f:\!:'1~'C"?"~~~:J~~il!":t~::tf;:~~,~~~;t~:-,~~~>>::~~c_ =.,:,~~i~~;~F: - <br /> <br /> <br />FraziI ice formed a second time during February 13 . 16. During this period small amounts of fraziI ice <br />formed below Split Mountain Canyon, but melted by 1000 to 1100 hIs. No lily-pad ice was observed. <br /> <br />5.2.2 Surface Ice <br /> <br />Surface ice formed along shorelines and in aU reaches of !be study area. Shoreline ice began fanning !be we.::k <br />of January 31 through February 4. Ice formation was minim~l. typica11y encnding less !ban a meter from <br />shore. After this initial formation, shoreline ice steadily decreased and was absent by late Febrnary. INo <br />smooth surface ice extending the width of the channel was observed in the study area. Aerial reronn.kunce <br />of the region on Febrnary 16 revealed sections of smooth surface ice near Sand Wash (approDmately 30 river <br />miles below Ouray, UT) <br /> <br />5.2.3 Jam Ice <br /> <br />Ice jams began fonning in narrow portions of the Green River at Ouray approximately Febnwy L Ice jams <br />were aeated by dislodged surface ice and lily-pad ice transponed from npstream. Jams 1Drmed in constricted <br />areas of the channel often d.mming water and diverting Dow into dIy, hJgh water channels. Ii:c jams persisted . <br />in the Ouray area throughout Febrnary breaking up Febrnary 28 - MardI 4. <br /> <br />10 <br /> <br />- <br />- <br /> <br />, <br /> <br />- <br />- <br />I <br />- <br />- <br />- <br />- <br />J <br />- <br />- <br />- <br /> <br />6;0 RESULTS <br /> <br />The effectS of Dow regulation and ice fonnation on nursery habitat of age-'l Colorado squawfish was addressed <br />by assessing changes in bac:kwater habitat characteristics. Minimum physical and chemical habitat requirements <br />were designated and used to detennine if a backwater couId suppon fish through the winter. The Collowing <br />section outlines the aitcria used and provides a summary of wintm" eonditions in each backwater sampled. <br /> <br />6.1 MINIMUM HABITAT REQUIREMENTS <br /> <br />Minimum habitat requirements were designated Cor the pb.ysical and chemical characteristics of a backwater <br />(Table 5). If the surface area of usable habitat (habitat above the minimum requirements) became less than <br />30 mI, then the backwater was detennined unsuItable nlmCI)' habitaL A tniDimum of 30 m' was designated <br />acalrding to the minimum requirements for a suitable backwater used by the Interagency StaDdardiz.ed <br />Monitoring Program (McAda et aL 1994). <br /> <br />6.1.1 Phnlcal Habitat Criteria <br /> <br />Wintertime changes in the physical habitat of a backwater were principally related to: (I) reduaion of free <br />water due to ice formation, (2) inundation or reduction in size of backwaters by Duauations in river stage, and <br />(3) modifications to backwaters caused by changes in river clwutelmorphology. <br /> <br />Ice formation within backwaters reduces the amount of free waler within !be water column and subsequently <br />the amount of usable ltabitat with in a backwater. For this study, 0.3 ft (9.0 em) of free water between the <br />substrate and bottom of the ice cover was determiJled min;m.l.fOr"usable habitaL The aiterion 0[.0.3 ft was <br />used to acalunt for variations in undersurface of surface ice and unevenness of backwater substrate. Free <br />water depths Jess than 0.3 ft may allow for local isolation and enuapment of fish. Free water between ice <br />layers and/or on top of the ice was not considered usable ItabitaL <br /> <br />River stage can change with river Dow.s and/or ice formation. These OUCluations in stage can significantly alter <br />backwater habitats. Increases in river stage can nood high water channels, changing backwaters to Dow. <br />through channels. Conversely, reductions in river stage can isolate or reduce the size of backwater habitats. <br /> <br />i <br />~.... <br /> <br />... <br />