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<br />M <br />-.J <br />IV <br />~~ <br /> <br />~~~bl <br /> <br />It is important to understand that the depletions presented in table. <br />3.2 represent annual averages under present (either calendar year 1975 or <br />calendar year 1976) conditions of development, except as noted in the <br />table for New Mexico data (see appendix B for the same data on a State-by- <br />State basis). There are significant fluctuations in depletions from year <br />to year, particularly for agriculture and exports, even _though the level <br />of development (as measured, for example, by the acres devoted to irrigated <br />agriculture) may be said to be constant over a short period-of years. For <br />example, during the period 1971-1975, it is estimated that total Basin <br />consumption for agriculture ranged from slightly more than 2 maf per year <br />to a high of 2.39 maf per year, or a fluctuation of 15 to 20 percent. <br />Likewise, exports varied by more than .200 maf per year for the same per- <br />iod of record (U.S. Bureau of Reclamation, 1977a, pp. 26-29). <br /> <br />The reason for these variations can be explained by the fact that the <br />amount of water which junior water right holders can divert and consume is <br />a function of the runoff that occurs in each year (see chapter 8 for a <br />brief discussion of each State's water rights system). Thus, during years <br />of relatively high flows, water right holders divert water for longer <br />periods of time than in low-flow years, and therefore consume more water. <br />As a corollary, during years of relatively low runoff, junior water right- <br />holders (who, for economic reasons, have not constructed reservoirs to <br />capture spring runoff) divert, and therefore consume, less water. Further- <br />more, summer temperatures and precipitation can affect the amount of water <br />consumed from year to year. <br /> <br />..:,.:,..... <br />'-::.",,::l <br />";',; .~:. <br /> <br />Instream Uses. In addition to serving as sources of water supply <br />for a variety of consumptive uses, many nonconsumptive, instream uses <br />are made of the rivers of the Upper Basin. These include direct contact <br />recreational pursuits (fishing, kayaking, rafting, and tubing), as well <br />as other activities which are enhanced by the presence of a stream (e.g., <br />hiking, picnicking, and camping). Ecological values are also associated <br />with a stream environment, as, for example, in the habitat they provide <br />for nongame species of fish. <br /> <br />With respect to direct contact recreational activities, it is esti- <br />mated that over 325,000 activity days of use occurred in 1976 on the main <br />stems of the larger rivers in the Upper Basin (table 3.3). While data is <br />largely unavailable as to the level of use on smaller tributaries (almost <br />all of which use would be fishing), it is clear that total recreational use <br />in the Upper Basin is substantially greater than the above-cited figure. <br /> <br />3-10 <br />