2009-05-22_GENERAL DOCUMENTS - C1981044

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Yampa River Flows Flow in the Yampa River depends primarily on snowmelt from the winter snowpack on the high mountain slopes surrounding the drainage basin. The lower intermittent and ephemeral drainages produce only a small part of the total water yield of the basin (Colorado Water Conservation Board, 1969). About 64 percent of the flow occurs in May and June with up to 84 percent occurring from April to July at selected gaging stations within the drainage basin (Steele, et al., 1979). Minimum flows generally occur from August through February. Irons, et al. (1965) reported that summertime flows in streams of the basin from July through October generally include a large component of ground water discharge. Extremes recorded at the Maybell Gaging Station are a maximum flow of 17,900 cfs on May 19, 1917, and a minimum of 2.0 cfs on July 17-19, 1934. Annual variation in yield may also be great. Historical annual yield has varied from 345,000 acre-feet in 1977 to 2,135,000 acre-feet for the Yampa River in 1917. Average annual yield amounts to 1,116,000 acre-feet. Williams Fork River Flows The Williams Fork River is a major tributary of the Yampa River. The Williams Fork drains approximately 350 square miles, or ten percent of the Yampa River Valley. The Williams Fork fluctuates seasonally like the Yampa, but is more dependent on snowmelt, and there is less ground water discharge to sustain the flows of the river during low flow periods. Flows in the Williams Fork in the permit area typically range between 2500 cfs during spring runoff and less than 100 cfs during low flow. Yampa River Sediment Load. In addition to yield, water quality also varies seasonally. Total suspended sediment loads are at a maximum during peak flows associated with spring runoff. Steele et al. (1979) reports that up to 90 percent of the annual sediment load of the Yampa River at the Maybell Station is discharged during the period of snowmelt runoff. Total suspended sediment loads increase with increased discharges (flows) in the rivers. Dissolved solids loads show an inverse relationship with stream discharges. Runoff Water Quality. High quality snowmelt runoff contains fairly low levels of total dissolved solids (TDS). Therefore, concentrations of TDS decrease during peak flow periods. In the summer, when ground water discharge makes up a larger percentage of the flow in the rivers, TDS values increase. The Colorado Water Conservation Board (1969) reports that intermittent (and ephemeral) drainages at lower elevations contribute most of the dissolved and suspended solids that leave the basin. Water Quality in Yampa and Williams Fork Rivers The dominant cations in the Yampa and Williams Fork Rivers are calcium, sodium, and magnesium. Dominant anions are bicarbonate and sulfate with minor chloride. The concentration of total dissolved solids (TDS) averages around 270 mg/1 in the Yampa River immediately below its confluence with the Williams Fork River. The Williams Fork increases the Yampa River's TDS concentration by less than 20 mg/l. The concentration in the Williams Fork averages around 300 mg/l. Use of Yampa River Water. Water within the Yampa River Basin is consumed through the irrigation of croplands, municipal water supplies, stock watering, cooling water for power plants, evapotranspiration by riparian vegetation and phreatophytes, and transbasin diversions. Irrigation of cropland constitutes the largest of these uses. Surface water consumed within the Yampa River drainage basin in 1976 totaled approximately 445,000 acre-feet. Of that, 399,000 acre-feet were used for irrigating croplands and hay meadows or for watering livestock. Other Eagle Mine Complex 6 Permit Renewal 05 C-1981-044 May 22, 2009