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, ;L ".. DRAFT 12/23/93 RECLAMATION PROPOSED SURPLUS GUIDELINES Basis for lruidelines. As part of the Annual Operating Plan, the Secretary of the Interior is required to make several determinations for that year regarding Colorado River operations. Among these, a Secretarial determination of surplus can be made when sufficient mainstream storage is available for release during the year to satisfy consumptive use in the Lower Division States in excess of 7.5 million acre-feet (maf) '. In preparing these guidelines for surplus determination, the Bureau of Reclamation (Reclamation) has taken into consideration system-wide consumptive use (depletions), critical periods of record, and estimated available water supply based on the past 85 years of hydrologic record. Reclamation examined the effect of alternate provisions for determining surplus, by developing operating scenarios and simulating the effects using the Colorado River Simulation System (CRSS), and CRSS-EZ models. Initial methods focused on alternate surplus threshold capacities or alternate percentage assurance of avoidance of spill strategies. Evaluations were made displaying the future effects on the occurrences of surpluses and shortages. Neither of these methods was founded on a technical or legal basis. Since the methods were more or less arbitrary, support for a strategy depended on the projected surplus and protection benefits. During the study, hydrologic and depletion forecasts changed, significantly altering the projected effects and benefits of each strategy. Dependable conclusions could not be maintained. If there is no legal or technical rationale for a strategy, there is no foundation that maintains the strategy over time and change. In the lower basin, the governing principal that appears to dominate the water supply, under full development conditions, is the recognition that within the lower basin the total of uses and losses exceed the total of the intervening flows plus the 8.23 maf objective minimum release from the upper basin. Rather than restrict the amount of full dependable development, the lower basin relies upon the application of shortage provisions to reduce depktion levels during times of long-term drought. Under full development, the 8.23 maf plus intervening flows is balanced by determining a shortage to the Central Arizona Project (CAP) and the Southern Nevada Water System (SNWS) as much as about 40 percent of the years. As a shortage determination will be common under full development Refer to the Criteria for Coordinated Long-Range Operation of Colorado River Reservoirs Pursuant to the Colorado River Basin Project Act of September 30, 1968 (p.L. 90-537) and the 1964 Supreme Court Decision in Arizona v. California. 1