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<br />~- <br /> <br />separate components. polluting constituents and temperature. as it relates to the downstream trout fishery ill the <br />Dolores River. <br /> <br />POLLUTING CONSTITUENTS <br /> <br />The major polluting constituents introduced into the Dolores River have historically been heavy metals, <br />acid and silt associated with mining and gravel operations near Rico, Colorado. Evidence of these contaminants <br />is nonnally not detectable where the river flows past the town of Dolores. due to natural filtering and buffering <br />processes. Chemical analysis of water samples taken at Dolores from 1989 through 1993 indicate that pH. total <br />dissolved solids and inorganic clements are below the Environmental Protection Agency existing and proposed <br />maximum contaminant levels for drinking water. The same infonnation concerning water quality is not available <br />for McPhee Reservoir or the area immediately downstream from the dam. <br /> <br />During six river trips in 1990-1991, water quality was measured by Bio/West, Inc. at six locations along <br />the Dolores River from Slick Rock to the Colorado River confluence (Valdez 1992). Bio/West reported that <br />"...water quality in the river was suitable for Colorado squawfish and other native species....". Several water <br />samples were tested for dissolved oxygen content in the river from McPhee Dam to Bradfield Bridge during the <br />period of 20 cfs flows in 1990. All samples were found to be saturated with oxygen. Problems associated with <br />low dissolved oxygen levels have not been reported in the past. There been no reports of fish symptoms <br />associated with nitrogen supersaturation. Nitrogen supersaturation occurs when nitrogen is forced into water <br />above aonospheric pressure. This usually occurs in lakes and reservoirs during cooler periods of the year when <br />activity decreases among bacteria which feed on nitrogen. If water supersaturated with nitrogen is released over <br />a spillway, without allowing sufficient exposure of the water to the aonosphere, aquatic life downstream may <br />become exposed to the high concentrations of nitrogen causing adverse physical effects. This problem has been <br />solved in the design of recently constructed dams. including McPhee Dam. by providing mechanisms for water <br />released through the spillway to become exposed to the aonosphere. usually by use of an cbstrUction at the foot <br />of the spillway. . <br /> <br />As with mosttailwaters, turbidity is nonnally low for a few miles downstream of the dam during <br />releases of small volumes of water. Further downstream. larger tributaries, beginning with Salter and <br />Narraguinnep Canyons. contribute sediment during rainfall events. <br /> <br />TEMPERATURE <br /> <br />A major component of water quality related to aquatic life is water. temperarure. Cn the stretch of <br />Dolores River from McPhee Dam to about twelve miles downstream, water temperature is primarily a function <br />of flow (volume), air temperature and the temperature of released water from the dam. During low flows. <br />channel shading also becomes a factor. <br /> <br />Salmon ids (trout) grow and thrive best in water that is 50-65 degrees Fahrenheit. During the summer <br />months at low flows (less than 50 cfs), these temperatures are not sustainable in the river except in the'viciaity <br />of the dam. One method to extend cooler flows farther downstream is to release enough water so that little <br />change in water temperature can occur from the dam to Bradfield Bridge. Such flows are not available for <br />sustained release downstream. Another method would be releasing the coldest water available from the reservoir. <br />Conversely, providing the warmest possible water during the winter may help .to prevent icing. <br /> <br />There are four outlets through which water may be released from McP)!ee Reservoir; these may be used <br />individually or together to control the temperature of water released from McPhee Reservoir: <br /> <br />Snillway - The spillway of McPhee Dam is a gated concrete structure located on the right abutment of <br />lhe dam. TIle spillway is intended for emergency use only. It has been used twice since the dam was <br />constructed. The lirst was during a te$t of ils operation shonly after Ihe reservoir filled in 1987. The <br /> <br />31 <br />