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Table 1. Purpose and dates of fields trips on the Green River for the winter ice study. Purpose 1993-94 Dates Autumn Mapping and Reconnaissance Winter Ice Measurements I September 28 - October 1, 1993 January 31 - February 4, 1994 February 10, 1994 February 16, 1994 February 21-24, 1994 Ground Reconnaissance of Study Area (UDWR) Aerial Reconnaissance of Study Area Winter Ice Measurements II 1994-95 A utumn Mapping and Reconnaissance W inter Ice Measurements I Winter Ice Measurements II October 20-23, 1994 January 6-8, 1995 February 6-8, 1995 Backwaters were selected in each of the three reaches based on area, depth, and formation classification (i.e. chute channel, scour channel, and eddy return channel). Chute channels typically {()rm in old side channels and along the shoreline interface of large exposed sand bars; scour channels frequently occur at the lower ends and margins oflarge sand bars and islands; eddy return channels form in association with large recirculation zones or eddies, immediately downstream from a channel constriction, e.g., debris fan (Rubin et al. 1990, Schmidt 1996). Backwaters within each rcach were selected with similar minimum area and formation classifications. Consideration was also given to accessibility of backwaters during winter months when ice cover prevents open water boat travel. A map of the shoreline and bathymetry was developed for each backwater selected. The shoreline was mapped on 43 x 56-cm paper using a plane table and an alidade. Prominent features (c.g.. trees, logs, and rocks) and principal substrate types (i.e., boulder, cobble, gravel, sand, and silt) wcre included on the map. Cont~ur isopleths were developed by measuring depth and area of free water, thickness of ice layers (surface ice, ice lenses, frazil ice), and current velocity along five to seven transects across each backwater. Depths were recorded in feet for consistency with the Interagency Standardized Monitoring Program (ISMP; McAda et al. 1994) backwater sampling protocol and converted to meters. Measurements were made with a staff gage through holes drilled in the ice. Holes were made using an ice chisel or a gas-powered ice auger with a 20-cm blade. Water velocity was measured with a Marsh-McBimey current meter. Each map was transferred to AutoCAD, a computer-aided design package to facilitate analyses and presentation. These habitat maps were reduced and printed on 22 x 28-cm paper for use as base maps during winter measurements (see Appendix A). 6