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Projected Plan of Operation Under Criteria - Water Year 1987 Determination of "602 (a) Storage" Section 602(a)(3) of the Colorado River Basin Project Act of September 30, 1968 (Public Law 90-537), provides for the storage of Colorado River water, not required to be released under article m( c) and m( d) of the Colorado River Compact in Upper Basin reservoirs, to the extent the Secretary of the Interior (Secretary) fmds it necessary to assure Compact deliveries without impairment of annual consumptive uses in the Upper Basin. Article 11 of the "Criteria for Coordinated Long-Range Operation of Colorado River Reservoirs" (Operating Criteria) provides that the annual plan of operation shall include a determination by the Secretary of the quantity of water considered necessary to be in Upper Basin storage as of September 30 of the current year. This determination shall consider all applicable laws and relevant factors including, but not limited to tbe following: <a) historic streamflows; (b) the most critical period of record; (c) probabilities of water supply; (d) estimated future depletions in the Upper Basin, including the effects of recurrence of critical periods of water supply; (e) the "Report of the Committee on Probabilities and Test Studies to tbe Task Force on Operating Criteria for the Colorado River," dated October 30,1969, and such additional studies as the Secretary deems necessary; and (f) the necessity to assure that Upper Basin consumptive uses 3re not impaired because of failure to store suFficient water to assure deliveries under section 602(a)(1) and (2) of Public Law 90-537. Taking into consideration these relevant factors, the Secretary has determined that the active storage in Upper Basin reservoirs forecast for September 30, 1987, exceeds the "602(a) Storage" requirement under any reasonable range of assumptions which might be applied to those items previously listed. Therefore, the accumulation of "602(a) Storage" is not the criterion governing the release of water during the current year. Mexican Treaty Obligations Annual calendar year schedules of monthly deliveries of water in the limitrophe section of the Colorado River, allotted in accordance with the Mexican Water Treaty signed in 1944, are formulated by the Mexican Section and preseoted to the United States Section, International Boundary and Water Commission (Commission), before the beginning of each calendar year. Upon 30 days advance notice to tbe United States Section, Mexico bas the right to modify, within the total schedule, any monthly quantiry prescribed by the schedule by not more than 20 percent. Ouring water year 1986, Mexico received a total delivery of about 10,780,000 acre-feet at the Northerly Imernational Boundary (NIB). Ofthe 10,780,000 acre-feet of mainstem Colorado River water reaching tbe NIB, about 4,900,000 acre-feet were delivered through tbe Pilot Knob Powerplant and Wasteway from the All-American Canal. An estimated 5,600,000 acre-feet were released through Laguna Dam. The remainder of the flow at NIB was made up of return flows to the Colorado River below Laguna Oam and returns to the Gila River below tbe gaging station near Dome, as well as Gila River flood control releases from Painted Rock Reservoir. Because of the current water supply conditions, the United States will make scheduled deliveries of 1,700,000 acre-feet of Colorado River water to the Republic of Mexico in calendar year 1987. Under most probable water supply conditions, flow at the NIB would total approximately 6.6 MAF during calendar year 1987. Such release of water is based upon average runoff conditions for the year. Should tbe runoff during 1987 be substantially above average, significant releases for flood control purposes could be required from Hoover Dam. Representatives of the Republic of Mexico will be kept informed of operating schedules through tbe United States Section of tbe Commission. 3