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I I I I I I I I I I I I I I I I I I I of the study, releases were made with maximum allowable fluctuations, and in the second year, releases were relatively steady. A more detailed description of these releases is provided in Section 4.0 Hydrology. Special releases from the dam were made in cooperation with Bureau of Reclamation and Western Area Power Administration. Flow release data from Flaming Gorge Dam were provided by Bureau of Reclamation, Salt Lake City Office (Courtesy of Tom Ryan and Brad Vickers, Bureau of Reclamation). Data on flows and water temperature for the Green River were obtained from the U.S. Geological Survey (USGS) stream gage located near Jensen, UT (station 09261000). Air temperature data were obtained from the National Oceanic and Atmospheric Administration (NOAA) weather station located in Jensen. Historic flow and temperature data were summarized from USGS data compiled in the GeoSelect Colorado River Database, a CD-ROM format database produced by Hydrosphere Data Products, Inc. ~ 3.2 Backwater Mapping Backwaters were selected in each reach based on size and depth, formation classification (i. e. chute channel, scour channel, and eddy return channel), and access during winter months. Efforts were made to select backwaters within each reach that represented different depths and formation classifications. Consideration was also given to accessibility of backwaters during winter months when ice cover prevented open water boat travel. Changes in backwater morphology were not considered detrimental to habitat value so long as other minimum habitat requirements were not violated. Only backwaters which met the ISMP (McAda et al. 1994) minimum requirements for a suitable backwater (i.e., surface area of at least 30 m2 and maximum depth of at least 1.0 ft) were selected. A map of the shoreline and bathymetry was developed for each backwater selected. The shoreline was mapped on 17 x 22-inch paper using a plane table and an alidade. Prominent features (trees, logs and rocks) and principal substrate types (as boulder, cobble, gravel, sand and silt) were included on the map. Contour isopleths were developed by measuring water depth (in feet) along 5 to 7 transects across the backwater (depths were recorded in feet for consistency with the ISMP backwater sampling protocol). Each map was transferred to AutoCAD, a computer-aided design package to facilitate analyses and presentation. These habitat maps were reduced and printed on 8.5 x II-inch paper for use as base maps during winter measurements. 3.3 Winter Habitat Measurements The amount of nursery habitat was determined by measuring and mapping the physical and chemical characteristics of each backwater from transects through various regions of the backwater. Physical habitat was quantified in square meters by recording shoreline configuration, depth and area of free water, thickness ofice cover, and current velocity on the 8.5 x II-inch base maps. Depth offree water and thickness of surface and frazil ice were measured in feet (~.05 ft) with a staff gage through holes drilled in the ice. Holes were made using an ice chisel, or a Strikemaster 49 cc gas- powered ice auger with an 8-inch blade. Water velocity was measured with a Marsh-McBirney current meter. 5