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<. -2- INTRODUCTION " OoeratiDl! History of McPhee Reservoir McPhee Reservoir began storing water in the spring of 1984. This reservoir has a total maximum capacity of 381,051 acre-feet (AF) of water, with an inactive storage capacity of 152,000 AF, and an active storage capacity of 229,051 AF of water, according to the U.S. Bureau of Reclamation- Durango Projects Office (USBOR-DPO). According to USBOR-DPO published information, McPhee Reservoir reached a volume of 378,000 AF or more in 1987, 1988, and 1989. It attained a maximum volume just under 310,000 AF in 1990 and 368,600 AF in 1991. Thus, McPhee Reservoir filled to within 99% of its maximum capacity in 1987, 1988, and 1989; 81 % capacity in 1990; and 97% capacity in 1991. The data in Table 1 is a summation of the flow regime in the Dolores River below McPhee Dam since April 1984. This information is a quick reference for ascertaining the length and extent of spill periods, the range of the discharge during spills, summer flows and ranges of flow during non-spill periods, and median winter flow levels and ranges from 1984 through 1991. According to USBOR- DPO data, the average annual run-off into McPhee Reservoir is approximately 350,000 AF. Given that information, it is evident from the data in Table 1 that McPhee Reservoir began water storage operations in 1984 at the beginning of a 4-year period with above average run-off (1984-1987) followed by a 4-year period (1988-1991) of below average run-off. Table 1. Dolores River flow regime (cubic feet-per-second=cfs) below McPhee Reservoir versus AF inflow/water year, 1984 to 1991. Water Winter flows' Spill period & range Summer flows' year Inflow AFxlO" Mean Range Dates Range Mean Range 1984 580.3 - 4/10-7/2 700-3825 172 54-656 1985 611.0 167 32-1065 4/1-6/25 187-3700 69 50-187 1986 572.3 59 49-100 4/2-6/23 600-4461 131 77-501 1987 589.2 223 71-600 4/4-6/27 600-3324 163 46-269 1988 259.2 78 70-83 5/2-6/7 194-1201 79 77-81 1989 263.1 79 49-81 4/6-5/14 440-1001 82 70-107 1990 142.5 69 20-80 - 0 35' 20-75 1991 293.0 31 27-39 5/13-5/27 125-800 61 33-71 . Winter flow data is for October I-March 31 for water year. · Summer flow period data is for July I-September 30. 'Summer flow period for 1990 is April I-September 30, 1990.