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~ .' COllectively, California's Colorado River water needs in excess of its basic apportionment amount to about 300,000 to 400,000 acre-feet per year and are likely to remain at that level during the period of full reservoir conditions. This relatively low additional use is due to the fact that significant amounts of unused agricultural priority Colorado River water (300,000 to 400,000, acre-feet per year) have been available, and may remain available in the foreseeable future, to meet Colorado River water needs that would otherwise be in excess of California's basic apportionment. While use of river water in excess of its basic apportionment may be temporary and intermittent in nature, it represents a valued resource, especially if California's other supplies are impacted by below normal runoff. The only other Basin state that is likely to be capable of using river water in excess of its basic apportionment during this period is Arizona. This is not expected to occur at the earliest until about 1992, the time when the CAP becomes fully operational. Arizona's principal use of water in excess of its basic apportionment is anticipated to be ground water recharge which is presently under study. By definition, there are no additional water supply benefits to be gained by the Basin states from excess water, which is defined as water in excess of the Basin states' needs and reservoir conservation storage. Excess water, however, would provide additional water supply benefits to Mexico inasmuch as it would receive, temporarily, water above the 1.5 million acre-foot per year Mexican Water Treaty delivery obligation. In accordance with the 1944 Mexican Water Treaty, if there is Colorado River water in excess of the united states needs, as determined by the united States, an additional 200,000 acre-feet may be provided, but Mexico acquires no rights to more than 1.5 million acre-feet per year. Excess water reaching Mexico above the maximum scheduled delivery of 1.7 million acre-feet per year is subject to interruptions and occurs as the result of flood control releases and operational spills. Redistr ibution of excess water, when appropriate, would provide for more uniform deliveries to Mexico during the temporary period of full reservoir conditions. While there are no water supply benefits derived by advance release of excess water, there is an element of risk to conservation storage, if provisions are not imposed to safeguard against releasing any water that wouldn't have been released pursuant to the Hoover Dam flood control regulations. provisions for preserving conservation storage ar e discussed fur ther under the heading "M i t iga tion to Preserve Conservation Storage" and in the following chapter in which the recommended process for developing AOPs dur ing full reservoir conditions is discussed. -15-