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<br />88 the Colorado-Big Thompson. Duchesne
<br />Tunnel, Roberts Tunnel and more recent
<br />projects increased exports to about 727,000 acre.
<br />feet per year for 1976-80, with a peak in 1978 of
<br />852,000 acre-feet.
<br />
<br />EFFECTS OF WATER QUALITY
<br />ON WATER USERS
<br />
<br />Recreation, Asthetlcs, and
<br />Fisheries
<br />
<br />The major instream uses in the Colorado River
<br />include hydroelectric power, propagation offish
<br />and aquatic life, recreation (including
<br />swimming, waterskiing, boating, rafting, etc.),
<br />and esthetics. A number of conflicts among
<br />water uses have become prominent issues in
<br />recent years.
<br />
<br />Many tradeoffs exist in water quality,
<br />eutrophication, and esthetics, both in 8 reservoir
<br />and downstream, depending on the depth of
<br />reservoir withdrawal and the flushing rate. The
<br />depth of withdrawal influences the temperature
<br />and nutrient releases from 8 reservoir. These
<br />releases can now be controlled to some degree by
<br />the use of selective withdrawal structures;
<br />however, conflicts have Occurred in the operation
<br />oflhese facilities. The conflict stems from the
<br />difference in the optimum temperatures for cold
<br />water fish like trout and wenn water endemic or
<br />endangered species like the sQuawfish.
<br />
<br />In addition to downstream effects, the depth of
<br />withdrawal in reservoirs has become a
<br />significant issue concerning the productivity of
<br />reservoir fisheries, eutrophication, nutrient
<br />retention, salinity routing, esthetics, and
<br />evaporation.[5J At present, concerns exist about
<br />evaporation, temperature, and nutrient
<br />processes in Fontenelle and Flaming Gorge
<br />Reservoirs, Lake Powell, and Lake Mead.
<br />
<br />Economic
<br />
<br />In the Lower Basin, present peak salinity is
<br />approaching critical levels for some salt
<br />sensitive crops. While the water is suitable for
<br />irrigating most crops, salinity is high enough
<br />
<br />EFFECTS OF WA TER DUAL/TY ON WA TER USERS '7
<br />
<br />that special irrigation practices are necessary in
<br />some cases. At the present time, salinity is
<br />being maintained below the standards.
<br />Complete development of apportioned water by
<br />the States without salinity control measures
<br />would result in increases in salinity that Bre
<br />detrimental to agriculture.
<br />
<br />A consortium of water resource centers in the
<br />States of Arizona, California, Colorado, and
<br />Utah cooperated in 8 study funded by the Office
<br />of Water Research and Technology and the
<br />Bureau of Reclamation to assess the economic
<br />damages caused by various salt concentrations
<br />to agricultural and municipal water users. This
<br />study is documented in a report entitled Salinity
<br />Management Options for the Colorado River,
<br />Water Resources Planning Series Report
<br />P.78.003, June 1978.161
<br />
<br />Based upon the findings of that report,
<br />Reclamation has published a summary working
<br />document entitled Colorado Rh'er
<br />Salinity-Economic Impacts on Agricultural,
<br />Municipal. and Industrial Users. (7J The
<br />estimated future annual damages to the Lower
<br />Basin water users in 1976 dollars were $343,000
<br />for each 1 milligram per liter (mgIL) increase in
<br />total dissolved solids (TDS) at Imperial Dam
<br />when concentrations reach the range of
<br />875 mgfL to 1,225 mg/L. The damage figure is
<br />apprOximately $610,200 per mgIL in 1986
<br />dollars. These annual damages were calculated
<br />using the 1972 salinity standard of 879 mgIL
<br />(approved by EPA in 1975) and a projected
<br />full development salinity concentration of
<br />1,225 mgIL at Imperial Dam.
<br />
<br />The annual municipal damages are divided as
<br />follows: Metropolitan Water District, 54 percent;
<br />Central Arizona Project, 8 peTtent; and lower
<br />main stem users, 8 percenL Total Bgriculture
<br />annual damages are 30 percenL Industrial
<br />impairments and Upper Basin damages were
<br />not evaluated.
<br />
<br />Estimating Economic Impacts of Salinity of the
<br />Colorado River [33] summarizes findings from a
<br />study designed to develop a method of
<br />forecasting economic impacts of salinity of the
<br />Colorado River upon various users in the
<br />southwestern United States. One objective was
<br />to update, revise, clarify, and refine the
<br />
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