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and most of its tributaries. Snowmelt runoff occurs from about <br />• mid-April to mid-July and ranges from about 1,000 to 10,000 cfs in the <br />reach from Steamboat Springs to Hayden. base flow prevails for the <br />remainder of the year and ranges from a low of about 50 cfs upward to <br />200 to 300 cfs. <br />The quality of the Yampa River varies inversely with flow. During high <br />flow from snowmelt the river water is quite dilute with dissolved solids <br />ranging from 30 to 50 milligrams per liter (mg/1) and hardness from <br />about 25 to 75 mg/1. Trace element concentrations are near the <br />detection level except for iron which is from 20 to 50 micrograms per <br />liter. <br />During base flow periods the common cation constituents range upward to <br />30 to 40 mg/1 for calcium, 10 to 15 mg/1 for magnesium and 10 to 25 mg/1 <br />for sodium. Common anion concentrations during base flow for <br />bicarbonate range from about 60 to 140 mg/1 and for sulfate ranges from <br />• 30 to 100 mg/1. Chloride concentrations are low, ranging from about 1 <br />mg/1 at high flow to 15 mg/1 at low flow. Dissolved solids and hardness <br />concentrations at base flow are about 175 to 275 and 125 to 175 mg/1, <br />respectively. <br />Comparison of samples collected in 1975 and 1976 on the Yampa River <br />below Trout Creek near Milner and below the diversion near Hayden <br />indicate that the dissolved solids increase about 25 percent in this <br />reach of the river during periods of low flow. This increase is due to <br />inflow from several tributary streams that may be influenced by coal, <br />oil production, and general ranching and farming activities. <br />Additionally, the Yampa River flows across the outcrop of the Iles <br />Formation, which is more highly mineralized waters than other formations <br />in the general area. <br />• <br />2.04.5-2 <br />