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I I I I I I I I I I I I I I I I I I I 3.0 WATER SUPPLY El khead Creek i nfl ows to El khead Lake were estimated for the 1953 to 1985 water yea rs. Si nce hi stori ca 1 records for streamflow do not exi st at thi s location, records from an upstream gaging station on Elkhead Creek near Elkhead, Colorado, were adjusted to approximate historical flows at the reservoi r. Thi s gagi ng stati on measures streamfl ows resul ti ng from a 1i4.2 square mil e drainage area. The period of record is from April, 1953 to the present, and tilt:! average annual discharge at that location is about 39,800 acre-feet. The extremes dJrin) the period of record range from nJ flow at times to a maximum daily discharge of 1,890 cfs on May 15,1984. To approximate the fl ow at El khead Dam, monthly flows at the upstream gag; ng station were adjusted to account for differences in the contributi ng drainage areas. Monthly strea'11 flows were multiplied by the square root of the ratio of the draina)e areas, which is 1.79. The adjusted monthly flows were used as El khead Lake i nfl ows and assumed representati ve of the flows resulti ng from the 204.6 square mile drainage area. Storabl e reservoi r i nfl ows were determi ned by subtracti ng seni or water ri ghts from the adjusted monthly inflows. The senior direct floN rights are entitled to jivert at a maximum rate of about 82 cfs during the irrigation season. Rather than collecting historical diversion and use data, the senior direct flow rights were assumed to be diverted each year in the monthly pattern shown on Table IV.4. Nearly 25,000 acre-feet of water would be needed each year to fully sati sfy these seni or ri ghts. However, there frequently are not adequate 1 ate summer flows to supply these ri ghts. D'Jri ng !lay, June and July, runoff from snowmelt is usually sufficient to fill Elkhead Lake and meet the senior ri ghts. - 24 -