7762 - Laserfiche WebLink

Home Browse Search

10 I I I I I I I I I I I I I I I I I I I Frazil ice formed a second time during February 13 - 16. During this period small amounts of frazil ice formed below Split Mountain Canyon, but melted by 1000 to 1100 hrs. No lily-pad ice was observed. 5.2.2 Surface Ice Surface ice formed along shorelines and in all reaches of the study area. Shoreline ice began forming the week of January 31 through February 4. Ice formation was minimal, typically extending less than a meter from shore. After this initial formation, shoreline ice steadily decreased and was absent by late February. No smooth surface ice extending the width of the channel was observed in the study area. Aerial reconnaissance of the region on February 16 revealed sections of smooth surface ice near Sand Wash (approximately 30 river miles below Ouray, UT) 5.2.3 .Jam Ice Ice jams began forming in narrow portions of the Green River at Ouray approximately February 1. Ice jams were created by dislodged surface ice and lily-pad ice transported from upstream. Jams formed in constricted areas of the channel often damming water and diverting flow into dry, high water channels. Ice jams persisted in the Ouray area throughout February breaking up February 28 - March 4. 6.0 RESULTS The effects of flow regulation and ice formation on nursery habitat of age-O Colorado squawfish was addressed by assessing changes in backwater habitat characteristics. Minimum physical and chemical habitat requirements were designated and used to determine if a backwater could support fish through the winter. The following section outlines the criteria used and provides a summary of winter conditions in each backwater sampled. 6.1 MINIMUM HABITAT REQUIREMENTS Minimum habitat requirements were designated for the physical and chemical characteristics of a backwater (Table 5). If the surface area of usable habitat (habitat above the minimum requirements) became less than 30 m2, then the backwater was determined unsuitable nursery habitaL A minimum of 30 m2 was designated according to the minimum requirements for a suitable backwater used by the Interagency Standardized Monitoring Program (McAda et a1. 1994). 6.1.1 PhYSical Habitat Criteria Wintertime changes in the physical habitat of a backwater were principally related to: (1) reduction of free water due to ice formation, (2) inundation or reduction in size of backwaters by fluctuations in river stage, and (3) modifications to backwaters caused by changes in river channel morphology. Ice formation within backwaters reduces the amount of free water within the water column and subsequently the amount of usable habitat with in a backwater. For this study, 0.3 ft (9.0 em) of free water between the substrate and bottom of the ice cover was determined minimal for usable habitaL The criterion of 0.3 it was used to account for variations in undersurface of surface ice and unevenness of backwater substrate. Free water depths less than 0.3 it may allow for local isolation and entrapment of fish. Free water between ice layers and/or on top of the ice was not considered usable habitaL River stage can change with river flows and/or ice formation. These fluctuations in stage can significantly alter backwater habitats. Increases in river stage can flood high water channels, changing backwaters to flow- through channels. Conversely, reductions in river stage can isolate or reduce the size of backwater habitats.