WSP03310

• File Number: 8271.200
• Description: Colorado River Basin Salinity Control Program - Development and History - UCRB 13a Assessment
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 8/13/1979
• Title: WRC Study - Draft Summary Report
• Water Supply Pro - Doc Type: Report/Study

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In addition to serving as sources of water supply for a variety of
consumptive uses, many nonconsumptive, instream uses are made of the
rivers of the Upper Basin. These include direct.contact recreational
pursuits (e.g., fishing, kayaking, rafting, and tubing), as well as other
activities which are enhanced by the presence of a stream (e.g., hiking,
picnicking, and camping). Ecological values are also associated with a
stream environment, as, for example, in the habitat they provide for
nongame species of fish.

With respect to direct contact recreational activities, it is esti-
mated that .over 325,000 activity days of use occurred in 1976 on the main
stems of the larger rivers in the Upper Basin. While data is largely
unavailable as to the level of use on smaller tributaries (almost all of
which use would be for. fishing), it is clear that total recreational use
in the Upper Basin is substantially greater than the above-cited figure.

Given the depletions which occur under present (1975-l976) condi-
tions of development and the effects of the numerous reservoirs which have
been built in the Upper Basin,l the annual amount and monthly distribution
of stream flows have been substantially altered from what they naturally
would have been. The resulting hydrologic regime has been characterized
by estimating the distribution of flows which would occur over the long run
if present conditions of development and reservoir regulation were to re-
main unchanged for several decades (see table 3.4). Put another way, the
hydrologic regime has been depicted in the "steady state," or equilibrium,
condition to which it would come over the long run.

With respect to reservoir content in the "steady state" condition,
it is estimated that the mean active content of Blue Mesa, Morrow Point,
.Flaming Gorge, and Lake Powell. reservoirs would be ab~ut 85 to 90 percent
of their combined maximum live storage. Annual evaporation from the eRSP
reservoirs would average about 665,000 acre-feet, bringing total average
annual Upper Basin depletions to 3.8 msf.

It is important to note that the above-described "steady .state"
conditions are premised upon natural flow estimates for the period 1906-
1974, which'natural flows averaged 15.2 maf per year at Lees Ferry. If
the period 1930-1974 is used, with estimated average natural flows at Lees
Ferry of 13.8 maf per year (see fig. 3.1), the resulting characterization
of the hydrologic.regime changes quite a bit. For example, the

1. There are over 30 reservoirs in the Upper Basin, the maximum live
storage of which totals 34.5 maf. Of this, the ca5P reservoirs account
for 29.7 maf.

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