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The unsteady flow sub-model used continuity and momentum equations to describe river flow in finite difference form. The model solved these equations for each river cross section through multiple time steps. The model used surveyed or estimated Green River geometry to calculate discharge and stage at multiple cross sections of the river as a function of time, using the observed upstream discharge as input. The model was calibrated to match the water surface response to each alternate release schedule observed during the field survey. The UNET model was also modified to incorporate the dynamic formation of river ice covers as determined by the ice cover progression sub-model. The ice cover progression sub-model (Section 2.4.3) predicts the sections of the channel in which a stationary floating ice cover will form. The presence of a stationary ice cover in a section changes the hydraulic properties of that section. These changes include reducing the cross-sectional area of the channel available for flow, reducing the hydraulic radius of the channel cross section, and modifying the effective channel roughness. These changes in the hydraulic properties in turn influence the discharge and stage calculated by the unsteady flow sub-model. 2.4.1.1 Channel Geometry Data FLO Engineering, Inc. provided 37 surveyed cross sections for the Green River in the vicinity of the Ouray National Wildlife Refuge, between RM 248 and 265. These data were in the format of the HEC-2 water-surface profile model (U. S. Army 1990) and were calibrated to observed water levels at a measured flow of 15,500 cfs (FLO Engineering, Inc. 1996). Additional surveyed cross-section data were obtained from the Bureau of Land Management (BLM). These cross sections were also surveyed by FLO Engineering, Inc. in conjunction with the Recovery Program's Channel Monitoring Program, and were located in areas between RM 269 and 290 and in the vicinity of the Escalante Wetlands and Razorback Island (RM 305-312). The cross-sectional geometry for the remainder of the study reach was estimated from USGS 1:24,000 scale, 10-ft contour interval topographic maps and from depth measurements made during the 25-30 January 1997 field study. 2.4.1.2 Calibration of UNET Unsteady Flow Model Calibration options for the UNET model include adjustments of the channel bed roughness, the roughness of the ice cover and the ice cover thickness. In addition, the hydrographs of water stage simulated by the UNET model can be calibrated by malting minor changes in the conveyance and storage capacity of selected reaches of river. Conveyance (K) is defined as: 1.49 2 K= AR', n -11-