Dolores River DRAFT Correlation Report

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DRAFT DRAFT DRAFT (especially below Disappointment Creek), the presence of non-native predators and competitors for available habitat, water temperature, and hydrologic modification such as changes to the magnitude, timing, and frequency of peak discharges. There also remains uncertainty as to the reproductive strategies of these fish within the Dolores River, and ultimately, their population viability under current or proposed alternative flow management scenarios. II. Hydrology and Downstream Ecology Pre-McPhee Reservoir through Dolores Project Operations While the purpose of this correlation report is to provide a framework "to describe the amount of water expected to flow downstream of McPhee Reservoir through spills and base flow releases" [and] "realistic opportunities to enhance those flows", such opportunities need to be evaluated based on "an analysis of potential downstream environments." (DRD `Plan to Proceed') To set the stage for the analysis of potential downstream environments, the hydrology and downstream ecology of the Dolores River prior to McPhee dam will briefly be considered. Data from this period include gage records at Dolores and Bedrock, diversions from the Montezuma Valley Irrigation Company's (MVIC's) canals, and mainly anecdotal accounts of ecological conditions. Irrigation diversions from the Dolores were initiated in the late 1870s and early 1880s, and large irrigation diversions out of the basin through MVIC's Main Canal No. 1 began in 1886. Below is a brief discussion of the hydrology and downstream ecology prior to water diversions from the Dolores River, followed by a description of the period from initial MVIC diversions until McPhee Dam was closed in 1986. A. Pre-MVIC -Hydrology and Downstream Ecology Geologic evidence suggests that the Dolores River Canyon below McPhee Dam is a remnant course of the San Juan River, which was separated and redirected to the south by a geologic uplift. "The small town of Dolores is just to the right of the south end of McPhee Reservoir. The Dolores River then turns abruptly toward the northwest and enters Dolores Canyon in the upper left quadrant. Dolores Canyon continues northward across the anticline with the river forming a canyon over 2,000 feet deep. The ancestral San Juan River established this path some 50 million years ago. 50 million years ago, all drainage on the western slope of the Rocky 9/5/06 12