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Gunnison River /Aspinall Unit Temperature Analysis -Phase I Executive Summary, Page-B institutional constraints would severely limit the effectiveness of a flow-based temperature management approach. Data Collection. An extensive data collection program was completed during the summer of 2001. Much of the data required to conduct model development and calibration during phase II of the project were obtained. These data include meteorological, hydrological, and water temperature time series data, as well as physiographic and engineering data pertaining to reservoirs, dams, and river reaches.. Based on a review of the data, no additional field work was conducted during 2001. We did however recommend to George Smith of the FWS that temperature recording devices be placed at least temporarily near the mouths of the Uncompahgre and North Fork of the Gunnison Rivers to provide additional baseline-data on tributary inflow temperatures. Additionally, one or more temperature recording devices on the mainstem of the Gunnison and certain major tributaries above Blue Mesa Reservoir (e.g., Lake Fork, Cebolla, Willow, etc.) would be useful for development and calibration of a Blue Mesa temperature model. Data Analysis. The primary objective of phase I of this project was to determine whether or not modifications to the Aspinall Unit could result in warmer water temperatures downstream near Delta. Before undertaking a substantial model development program, the Recovery Program asked that we undertake,a preliminary analysis of the data with the purpose of 1) providing a preliminary analysis. of whether or not increased water temperatures are possible with reservoir modifications, and 2) what type(s) of modeling approach is most appropriate given the nature of the Gunnison system. Our scope for phase I was limited to some straightforward processing of data for visualization and preliminary statistical analyses. Nevertheless, the following conclusions can be drawn: 1. Stream temperatures near Delta are significantly impacted by Aspinall operations, and do not return to ambient conditions until somewhere downstream of Delta. 2. Blue Mesa Reservoir is the primary cause of cold-water releases from the Aspinall Unit. Crystal releases are warmer than those of Blue Mesa, indicating that Morrow Point and Crystal actually warm the river relative to Blue Mesa release temperatures. 3. Warmer water is physically available in Blue Mesa, and could be released . downstream with a TCD. Models of all three reservoirs would be useful in determining the impacts of such a structure on the thermal regimes of the reservoirs. 4. Tributary inflows do impact stream temperatures at Delta, but not with a frequency or magnitude to render potential reservoir control ineffective. 5. Warmer releases from Crystal would result in warmer river temperatures at Delta. Generally, release temperatures from Crystal would need to be increased about 3 °C to warm the river at Delta by 2 °C. 6. Stream temperatures at Delta show a strong statistical correlation to release temperatures and atmospheric conditions; thus, a statistical model could potentially be used in lieu of a more costly physically-based model of the river. Hydrosphere Resource Consultants