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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />C> <br />~ <br />~ <br />~ <br /> <br />-27- <br /> <br />I'asin is the dominant factor in the chemical quality of the <br /> <br />basin's waters.. Figure 5 depicts the surface water quality <br /> <br />concentrations associated with the various areas in the <br /> <br />upper Colorado River Basin. Comparing Figures 4 and 5 will <br /> <br />indicate the geologic importance to water quality. <br /> <br />WATER SUPPLY OF THE UPPER COLORADO RIVER <br /> <br />The largest and most prominent constraints to the water <br /> <br /> <br />supply in the Upper Basin are the various treaty and compact <br /> <br /> <br />rights. The 1922 Colorado River Compact guarantees a total <br /> <br /> <br />of 9.25 x 106 ha-m over each consecutive ten-year period to <br /> <br /> <br />the Lower Basin for an annual average of about 9.25 x 105 <br /> <br />ha-m. The 1944 Mexican Water Treaty effectively raised this <br />annual average amount to 1.02 x 106 ha-m, assuming that one- <br /> <br />half of the water promised to Mexico comes from the VCRB <br /> <br />allocation (Holburt, 1977). In addition, several other <br /> <br />legal, legislative and international obligations have tied <br />the salinity concentrations and control to the water supply. <br />Mann et al. (1974) produced an interesting legal-political <br />history of the Upper Basin which is helpful in understanding <br />the development of the Colorado River. <br /> <br />Precipitation <br /> <br />The majority of the water supply in the Colorado River <br /> <br />Basin comes from high mountain snowpacks. Flow duration <br /> <br />tables and curves describing the seasonal and annual water <br /> <br />supply variability of the Upper Colorado River and its major <br /> <br />tributaries are presented by Iorns et al. (1965). Extreme <br /> <br />~ <br />