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<br />To, the contrary, there are significa~t fluctuations in depletions from
<br />year to year, particularly for agriculture and exports, even though the
<br />level of development (as measured, for example, by the acres devoted
<br />to irrigated agritulture) may be said to be constant over a short period
<br />o~ years, For example, during the period from 1971 through 1975, it is
<br />" estimated that total Upper Basin consumption for agriculture ranged from
<br />~ slightly more than 2 maf per year to a high of 2.39 maf per year, or a
<br />~ fluctuation of 15 to 20 percent. Likewise, exports varied by more than
<br />:J .200 maf per year for the same period of record (U.S. Department of the
<br />Interior.. 1978, pp, 32-36).
<br />
<br />The reason for these variations can be explained by the fact that
<br />the amount'of water which junior water right holders (see chapter 7 for
<br />a brief discussion of each state's water rights system) can divert and
<br />consume is a function of the runoff that occurs in each year, Thus,
<br />during years of relatively high flows, water rights holders divert water
<br />for longer periods of time than in low flow years, and therefore consume
<br />more water. ,As a corollary, during years of relatively low runoff,
<br />junior water right holders (who, for economic reasons, have not con-
<br />structed reservoirs to capture spring runoff) divert must divert less,
<br />a~d therefore consume less water.
<br />
<br />.
<br />
<br />Instream Uses. In addition to serving as sources of water supply
<br />for a variety of consumptive uses, many non-consumptive, 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 non-game species of fish.
<br />
<br />With respect to direct contact recreational activities, it is
<br />estimated that over 325,000 activity days of use occurred in 1976 on
<br />the main stems of the larger rivers in the Upper Basin (Table 3.3).,
<br />While data are largely unavailable as to the level of use on smaller
<br />tributaries (almost all of which use would be fishing) it is clear that
<br />total recreational use in the Upper Basin is substantially greater than
<br />the above cited figure,
<br />
<br />PRESENT HYDROLOGIC CONDITIONS
<br />
<br />Given the depletions "hich occur under present (1975-1976) levels
<br />of development, as discussed above, and the effect of the numerous
<br />reservoirs which have been built in the Upper Basin, the annual amount
<br />and monthly distribution of stream flows has been substanti~lly altered
<br />from what it naturally would have been, The resulting hydrologic con-
<br />ditions can be characterized in two different ways, each of which
<br />
<br />.
<br />
<br />1. The active stotage of all reservoirs in the Upper Basin totals 34,5
<br />maf. Of this, the Colorado River Storage Project reservoirs account
<br />for 29,7 maf (U,S, Bureau of Reclamation, 1978, p. 24). The purpose of
<br />these latter reservoirs is to store water for delivery to the Lower
<br />Basin states.
<br />
<br />3-9
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