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Projected Plan of Operation Under Criteria - Water Year 1989 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 lU(c) and III(d) of the Colorado River Compact in Upper Basin reservoirs, to the extent the Secretary of the Interior (Secretary) [rods it necessary to assure compact deliveries without impairment of annual consumptive uses in the Upper Basin. Article II of the "Criteria for Coordinated Long,Range Operation of Colorado River Reservoirs" (Operatiog 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 the 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 the Task Force on Operating Criteria for the Colorado River," dated October 30, 1969, and such additional studies as the Secretary deems necessary; and (I) the necessity to assure that Upper Basin consumptive uses are not impaired because of faiJure 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, 1989, 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 of 1944, are formulated by the Mexican Section and presented to the United States Section, International Boundary and Water Commission (Commission), before the beginning of each calendar year. Upon 30 days advance notice to the United States Section, Mexico has the right to modify, within the total schedule, any monthly quantity prescribed by the schedule by not more than 20 percent During water year 1988, Mexico received a total delivery of about 2,700,000 acre,feet at the Northerly International Boundary (NIB). Of the 2,700,000 acre-feet of mainstem Colorado River water reaching the NIB, about 1,560,000 acre-feet were delivered through the Pilot Knob Powerplant and Wasteway from the All-American CanaL An estimated 510,000 acre-feet were released through Laguna Dam. The remainder ofthe flow at NIB was made up of return flows to the Colorado River below Laguna Dam, and returns to thc Gila Rivcr below the gaging station near Dome, as well as small Gila River releases from Painted Rock Reservoir. Beca use of the current water supply conditions, the United States will make scheduled deliveries of 1,500,000 acre-feet of Colorado River water to the Republic of Mexico in calendar year 1989. Under most probable water supply conditions, flow at the Nffi will total approximately 1.6 MAF during calendar year 1989, due to a small amount of additional water being released while Senator Wash Reservoir is out of operation for repairs and testing. Representatives of the Republic of Mexico will be kept informed of operating schedules through the United States Section of the Commission. 3