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. . . DRAFT 1992 Water Accounting Report to the Rio Grande Compact Conmission Engineer Advisors SAN JUAN-CHAKA PROJECT Heron Reservoir Computations of the Rio Grande basin inflow to Heron Reservoir were made using the ratio method for 1992. The ratio method is the basis in the determination of the natural flow (Rio Grande) within the Willow Creek drainage area. The daily volume was measured directly using the Willow Creek above Heron gage, and when San Juan-Chama (SJ- C) diversions were in progress, the gaged flow was adjusted for Azotea Tunnel outlet gaged flow less a small channel loss. The natural volume was then adjusted by the appropriate historical correlation factor to arrive at the amount to be bypassed at Heron Dam. The correlation factors were developed using the historical gage data for Willow Creek above Heron Reservoir and Willow Creek at parkview (Heron Dam) . Frequency analyses of the streamflow data for Willow Creek at parkview betyeen 1943 and 1970 indicate that flows of 1 cubic foot per second (ft Is) were exceeded approximately 60 % of the time. The mean annual streamflow val~es indicate only one year in the period that averaged lers than 2 ft Is. Seepage from Heron Dam averages between 2 and 3 ft /s at current storage levels. Thus, the base flow of Willow Creek at Heron Dam (Rio Grande flow) approximates the seepage from the dam. Table 1 (page 1) illustrates the computed natural flow at Heron Reservoir using the seepage. as the base flow. Table 2 (page 2) computes the unaccounted gains or losses on the reservoir. Gains in excess of the net evaporation volume computed for the month were considered nat-ural gains and subsequently delivered as Rio Grande water. Table 3 (page 3) illustrates actual operations of Heron Reservoir for 1992. Column 5 is a balance between the end of the month contents using the operational inflow and outflow data. Table 4 (page 4) lists SJ-C water delivered for each contractor from Heron Reservoir in 1992. Diversions were maximized to offset deliveries and losses from Heron Reservoir in 1992. In the previous fall, good precipitation developed, and with a slightly above normal spring runoff and normal summer precipitation, the reservoir reached a maximum content _-Of. 401,569 acre-feet (AF) at elevation 7186.14 ft. QilJlliyi2,.1~!l.2' i 1/10 iB , I