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<br />d. Assumptions Made by Recent Studies <br /> <br />The GAO study assumes that the virgin flows of <br />the Colorado River at Lee Ferry will average 15.0 MAF/yr. <br />The Colorado DNR study assumes that such flows will range <br />between 13.8 and 15.2 MAF/yr. The EPA and the OTA studies <br />very roughly consider what might happen with a slightly lower <br />range of virgin flows. <br /> <br />2. 1922 Colorado River'Compact <br /> <br />a. Apportionment of consumptive use. <br /> <br />The 1922 Colorado River Compact apportions the <br />consumptive use of the entire Colorado River System, <br />literally including all tributary flows, between the Upper <br />and Lower Basins. (See Figure 1). Unfortunately, it was <br />consummated at a time when the virgin flows in the Colorado <br />River may have been abnormally high. The drafters assumed <br />that the Colorado River virgin flows averaged at least <br />16.0-18.0 MAF/year at Lee Ferry, and apportioned 7.5 MAF/year <br />of consumptive use to the Upper Basin, and 8.5 MAF/year to <br />the Lower Basin in Article III paragraphs (a) and (b) of the <br />Compact. <br /> <br />b. Upper Basin Delivery Obligation <br /> <br />Article III paragraphs (a) and (b) place <br />limits on the consumptive use of Colorado River water in the <br />Upper and Lower Basins, and also serve in defining when a <br />.surplus" exists for the purpose of delivering water to <br />Mexico. The actual division of water between the two basins, <br />however, occurs in Aricle III(d) which obligates the Upper <br />Basin to deliver 75.0 MAF to the Lower Basin at Lee Ferry <br />over a progressive 10 year period. This was agreed to by the <br />Upper Basin at that time because it appeared that the virgin <br />flows of the Colorado River gave the Upper Basin ample margin <br />in making this guarantee. Article III(d) could now have the <br />effect of allocating the reduction in the estimates of the ' <br />River's virgin flows to the Upper Basin. <br /> <br />c. Mexico Burden <br /> <br />The 1922 Compact anticipated that the United <br />States would proimise to make deliveries to Mexico from the <br />Colorado River. The drafters of the Compact, in their <br />generous estimate of virgin flows, provided in Article III(c) <br />that any such delivery would be made first from the expected <br />surplus over the 16.0 MAF/year necessary to supply the con- <br />sumptive use apportioned to the Upper and Lower Basins. As a <br />safeguard, Article III(d) further provided that the Mexico <br />Burden, in the event that no such surplus existed, would be <br />borne equally by the Upper and Lower Basins. In 1944, the <br /> <br />. ';;i~ ., <br /> <br />-11- <br />