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.. .., ol' . . Colorado River Compact Symposium James S. Lochhead Page 19 said States and to the Congress, and of formulating a comprehensive scheme of control and the improvement and utilization ~6 the water of the Colorado River and its tributaries. WHAT HAS SUBSEQUENT EXPERIENCE TAUGHT US? The Neqotiators OVer-Estimated the Water Supply It is impossible to negotiate any agreement, much less an interstate compact making a perpetual allocation of water, and anticipate every contingency. There were some issues, such as Indian reserved water rights and the obligation to Mexico, which were affirmatively put off by the Compact negotiators. However, the biggest variable was water supply. The negotiators had some idea of the water supply of the river system, and calculated uses based on the consumptive use of irrigation. However, the period of record with which they were dealing was extremely limited. Moreover, the years prior to 1922 were, it turns out, abundant water years. The negotiators made various estimates at water supply in the mainstem, which ranged from 18-19 million acre-feet per year. The significance of these discussions over water supply is evident from the obligation taken on by the upper Basin to not deplete the river below a ten-year running average of 75 million acre-feet. The upper Basin negotiators were comfortable that there was enough water in the river for their states to meet this obligation, and still have the ability to develop the 7.5 million-acre feet per year of consumption that was apportioned to them. Carpenter assured the Colorado legislature: The states of the Upper Division shall not cause the flow of the river at Lee Ferry to be depleted below an aggregate of 75,000,000 acre-feet for any period of ten consecutive years (7,500,000 acre-feet average annual flow over any ten year period) if necessary for use in the Lower Basin. This is approximately fifty per cent of the river flow at Lee Ferry during3Uhe lowest ten- year period of which we have a record. In the Colorado legislature's consideration of ratification of the compact, questions arose about the water supply estimates, and the adequacy of the water supply in the 36 37 43 U.S.C.A. 617n. Carpenter Report.