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4 UDENWLR290 4 U. Denv. Water L. Rev. 290 (Cite as: 4 U. Denv. Water L. Rev. 290) Page 13 determination of any Upper Basin obligations under the Mexican Treaty. [FN1181 *316 Ifi',operating Lake Mead under the Operating Criteria, tlie"Secretary makes determinations based on a number of factors, largely repeated from the Decree in Arizona v. California. [FN1191 In a "Nermal Year," annual pumping and release from Lake Mead will be sufficient to s.~tisfy 7.5 m.a,.f. of annual consumptive use in accordance with the Decree. [FN1201 In a "8111rplus Year" (when the Secretary determines that water in quantities greater than "normal" is available), the Secretary apportions 5el% of the surplus water to California, 46% tQAP'?:ona, and 4% to Nevada, as outlined in the Decree. [FN1211 If the Secretary determines a "Shortage" (water in quantities less than "normal" is available), uses are restricted in accordance with the Decree and the 1968 Act. [FN1221 X. SOME MAJOR ISSUES FOR THE UPPER BASIN UNDER THE LAW OF THE RIVER States, the United States, Indian Tribes, and water user organizations have exerted tremendous effort to establish a legal framework for determining rights to use and develop the waters of the Colorado River and to regulate its operation. Despite this effort, however, significant issues exist that threaten to undermine the security and certainty of supply created by that framework. The balance of Part I of this article will discuss some of these issues, which play into the relationships between the Upper Basin States and California. The fIrst issue regards the basic misunderstanding the Compact negotiators had concerning how much water was actually in the Colorado River System. The second issue relates to fundamental unresolved matters the negotiators left to future generations. The third issue stems from the fact that millions more people live in the Basin, and the regulatory environment and public values oftoday are considerably different and more complex than in 1922. Finally, some have argued that market mechanisms and water transfers should be allowed on an Upper to Lower Basin basis, to satisfy the increasing *317 demands in California and Nevada. A. The Compact Negotiators Over-Estimated Water Supply It is impossible to negotiate any agreement, much less an interstate compact making a perpetual allocation of water, and anticipate every contingency. The Compact negotiators affIrmatively put off some issues, such as Indian reserved water rights and the obligation to Mexico. However, the biggest variable was water supply, and it was an issue about which the Compact negotiators were simply mistaken. The negotiators had some idea of the water supply in the Colorado River System, and calculated uses based on the consumptive use of irrigation. However, the negotiators dealt with an extremely limited period of record. Moreover, the years prior to 1922 were actually abundant water years. The negotiators made various estimates of water supply in the mainstream, which ranged from;1.8 to 21 m.a.f./yr. The significance of these discussions over water supply is evident from the Upper Basin's obligation not to deplete the Colorado River below a ten-year running average of 75 m.a.f. The Upper Basin negotiators were comfortable that enough water existed in the Colorado River for their states to meet this obligation and still have the ability to develop the 7.5 m.a.f.lyr of consumption apportioned to them. In urging the Colorado legislature to ratify the Compact, Carpenter assured them: It is evident that the States of the Upper Basin may safely guarantee 75,000,000 acre-feet aggregate delivery at Lee Ferry during each ten-year period. This would mean an average annual delivery of 7,500,000 acre-feet as against 15,940,594 acre- feet present net annual average flow (100%) at Lee Ferry or 18,415,842 acre-feet natural average annual flow (100%) on the basis of a "reconstructed" river. [FN1231 Arthur Powell Davis, the Commissioner of Reclamation, backed Carpenter's and the other Commissioners' assurances. Davis had prior to and throughout the negotiations stated that plenty of water existed in the Colorado River System to take care of all existing and future anticipated uses. Unfortunately, history has shown these optimistic assumptions were just that. Since 1922, the undepleted flow of the Colorado River at Lee Ferry has averaged only 14.2 m.a.f./yr. Ten-year periods with a flow of 11.8 m.a.f.lyr have occurred twice in this century. [FN1241 Tree ring studies have estimated the long-term average supply at 13.5 m.a.f.lyr, and have put one ten-year period flow at 9.7 m.a.f.lyr. [FN1251 Table II below, and its accompanying notes, provides a comparison *318 between the assumptions made in 1922 and what we now know with the benefit of an additional eighty years of history. @ 2006 Thomson/West. No Claim to Orig. U.S. Govt. Works.