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<br />14 • <br />flooding of roads and fields, and plugging of water intake systems <br />far the mines. <br />The capability of a stream to maintain indigenous fish populations <br /> <br />is jeopardized when factors extrinsic to natural degradation are intro- <br />duced. These factors become critical only when the ~~lerance level for <br />a fish species is exceeded. <br />Excepting flood-producing rainstorms in summer, runoff is dominated <br />by snowmelt which creates high discharges generally between early May <br />and the end of July. Peak discharge at Stonewall during this period was <br />about 65 and 80 cfs in 1978 and 1979, respectively. Very low flows were <br />recorded from mid-September to mid-April each year, with minimum flows . <br />being 4 cfs at Stonewal]. These periods of low flow are of most concern <br />when considering welfare of fish. This is because of the reduced <br />capacity for dilution of any toxic or harmful effluents introduced into <br />the stream. <br />Water quality is monitored at a USGS surface water gaging station <br /> <br />at Stonewall, Colorado on the Middle Fork approximately 4 miles upstream <br />from the Allen Mine. Peasurements of water quality parameters at this <br />station were averaged in the Water, tJaste 8 Land, Ltd. (1980) report. <br />Of the chemical parameters reported, only a few can be related to the <br />welfare of fish populations. Measurements or" suspended solids and <br />turbidity, which may be of more consequence to the production of fish, <br />are not available from USGS. <br />~` <br />L. <br />