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River was apportioned to provide exclusive beneficial con-
<br />sumptive use of 7.5 million acre-ft annually to each basin,
<br />and the Lower Colorado River Basin was given the right to
<br />increase its annual beneficial consumptive use by 1 million
<br />acre-ft. The States of the upper division guaranteed to
<br />"***not cause the flow of the river at Lee Ferry to be
<br />depleted below an aggregate of 75 million acre-ft for any
<br />period of 10 consecutive years***". The Compact also made
<br />provisions for obligations to Indian tribes and stipulated that
<br />if flow proved insufficient to satisfy any treaty obligations
<br />to Mexico, "***the burden of such deficiency shall be equal-
<br />ly borne by the Upper basin and the Lower basin." Such
<br />an obligation was fulfilled by the Water Treaty of 1944 with
<br />the United Mexican States, which guaranteed 1.5 million
<br />acre-ft of water annually to Mexico.
<br />The Upper Colorado River Basin Compact of 1948
<br />apportioned the water of the Upper Colorado River Basin
<br />among the five States having drainage areas that contribute
<br />to the flow of the Colorado River upstream from Lee Ferry,
<br />Ariz. Annual consumptive use was allocated as follows:
<br />50,000 acre-ft to Arizona, and of the remaining portion,
<br />51.75 percent to Colorado, 11.25 percent to New Mexico,
<br />23 percent to Utah, and 14 percent to Wyoming.
<br />Although it did not directly apportion flow, the Colo-
<br />rado River Storage Project Act of 1956 (Public Law 84-485)
<br />resulted in major effects on the flow in the entire Colorado
<br />River basin. It authorized construction of the Glen Canyon
<br />Dam, the Flaming Gorge Dam, the Navajo Dam, and the
<br />Wayne N. Aspinall (formerly known as Curecanti) Unit,
<br />which is composed of Blue Mesa, Morrow Point, and Crystal
<br />Reservoirs on the Gunnison River.
<br />Water Quality
<br />The Water Quality Act of 1965 (Public Law 89-234)
<br />was an amendment to the Federal Water Pollution Control
<br />Act of 1948. It required States to adopt water-quality stand-
<br />ards for their interstate waters, but did not require numeric
<br />criteria for dissolved-solids concentrations. A second set of
<br />amendments, Public Law 92-500, was enacted in 1972. The
<br />U.S. Environmental Protection Agency's interpretation of
<br />this law required the establishment of numeric criteria for
<br />dissolved-solids concentration in the Colorado River. The
<br />Colorado River Basin Salinity Control Forum was established
<br />to develop these criteria and a plan of implementation. The
<br />Forum recommended that numeric dissolved-solids criteria
<br />be set at the calculated flow-weighted concentrations that
<br />existed during the 1972 calendar year (Colorado River Basin
<br />Salinity Control Forum, 1975). These were approved by the
<br />seven basin States and the U.S. Environmental Protection
<br />Agency in 1976. The criteria are dissolved-solids concen-
<br />trations of 723 mg/L downstream from Hoover Dam,
<br />Arizona-Nevada, 747 mg/L downstream from Parker Dam,
<br />Arizona-California, and 879 mg/L upstream from Imperial
<br />Dam, Arizona-California.
<br />An outcome of the 1972 meeting between President
<br />Nixon and Mexican President Echeverria was the signing
<br />of Minute 242 of the International Boundary and Water Com-
<br />mission pledging to find a solution for Mexico's problems
<br />with saline Colorado River water. It was agreed that the dif-
<br />ference between the average annual salinity at Morelos Dam
<br />(at the Mexican border) and at Imperial Dam (the last major
<br />control structure upstream from the Mexican border) should
<br />not exceed "115 ± 30 parts per million" (Upper Colorado
<br />River Commission, 1973).
<br />Congress passed the Colorado River Basin Salinity
<br />Control Act (Public Law 93-320) in 1974 authorizing the con-
<br />struction of 4 salinity-control projects and the development
<br />of plans for 12 others. The 1984 amendment to the act (Public
<br />Law 98-589) provided authority to the U.S. Bureau of
<br />Reclamation and the U.S. Department of Agriculture to in-
<br />stall the salinity controls needed to meet the numeric criteria
<br />through the year 2005. The amendment established cost
<br />effectiveness as an underlying decision-making criterion for
<br />implementation of a project, authorized construction of
<br />several projects, and authorized the Secretary of Agriculture
<br />to establish a voluntary on-farm salinity control program with
<br />landowners (U.S. Bureau of Reclamation, 1985b).
<br />METHODS OF DATA ANALYSIS
<br />The primary source of the data used in this report was
<br />the U.S. Geological Survey's National Water Data Storage
<br />and Retrieval System (WATSTORE) (Hutchison, 1975). All
<br />daily values of streamflow and specific conductance and
<br />analyses of water quality were retrieved from this data base.
<br />Data describing streamflow-gaging stations, such as location
<br />and elevation, were obtained from WATSTORE and U.S.
<br />Geological Survey data reports. Much of the data for reser-
<br />voirs, diversions, and agricultural projects were obtained
<br />from the U.S. Bureau of Reclamation project data reports
<br />(U.S. Water and Power Resources Service, 1981), and addi-
<br />tional data were obtained from the U.S. Department of the
<br />Interior progress report (1985) and the Upper Colorado River
<br />Commission (1950-84) annual reports.
<br />Daily data collection in the Upper Colorado River
<br />Basin by the U.S. Geological Survey began in 1894 when
<br />streamflow-gaging stations were established along the Colo-
<br />rado and Gunnison Rivers near Grand Junction, Colo., and
<br />along the Green River near Green River, Wyo., and Green
<br />River, Utah (U.S. Geological Survey, 1954). Daily monitor-
<br />ing of specific conductance began in 1935 when once-daily
<br />measurements were recorded at stations along the Colorado
<br />River near Cameo, Colo., and Cisco, Utah, and along the
<br />Gunnison River near Grand Junction, Colo.
<br />Systematic sampling of water quality in the Upper
<br />Colorado River Basin began in 1926, when 10 samples were
<br />analyzed from the Colorado River at Lees Ferry, Ariz.
<br />(Collins and Howard, 1928). By 1984, water at 566 different
<br />14 Characteristics and Trends of Streamflow and Dissolved Solids in the Colorado River Basin
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