9521

• UCREFRP Catalog Number: 9521
• Author: Liebermann, T. D., D. K. Mueller, J. E. Kircher and A. F. Choquette.
• Title: Characteristics and Trends of Streamflow and Dissolved Solids in the Upper Colorado River Basin, Arizona, Colorado, New Mexico, Utah, and Wyoming.
• USFW Year: 1989.
• USFW - Doc Type: Denver.
• Copyright Material: NO

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1955 1960 1965 1970
WATER YEAR
Figure 24. Daily streamflow at site 69 (Colorado River at Lees Ferry, Ariz.).
dissolved-solids load throughout the year. Mean annual
streamflow averaged about 11.5 million acre-ft during
1942-62 (table 9). Annual inflows to Lake Powell during
the principal filling period (1966-80) averaged 10.8 million
acre-ft, and annual outflows were about 8.8 million acre-ft,
representing a mean annual depletion of 2 million acre-ft.
This depletion was a result of increased storage in the reser-
voir, losses through net evaporation, and losses to net bank
storage. After normal operation was established in 1965,
most releases of reservoir water were through the power-
plant. Although day-to-day variations in release were large,
the annual variations in daily streamflow were much less than
in the past. During the principal filling period, streamflow
had no snowmelt-season peak (fig. 25C). Slight increases
in releases during the winter and summer months indicated
seasonal increases in power demand for heating and air
conditioning.
Streamflow releases during the initial filling period had
relatively high dissolved-solids concentrations because of
unusually low inflows. After 1968, the overall dissolved-
solids concentration in the reservoir had stabilized. Mean
annual dissolved-solids concentration at site 69 was not
significantly affected by the reservoir. During 1966-80, the
mean annual flow-weighted dissolved-solids concentration
was 564 mg/L, an increase of less than 5 percent of the
1975 1980 1985
1942-62 mean annual flow-weighted concentration (539
mg/L). Mean annual dissolved-solids load, however,
decreased from about 8.4 to 6.7 million tons/yr (table 9),
because of the decrease in streamflow. During the principal
filling period, calcium, sodium, and sulfate were the pre-
dominant ions throughout the year. The monthly variation
in dissolved-solids concentration, load, and chemical com-
position was very small. Since the end of the principal fill-
ing period, the record is too short for average conditions of
streamflow and dissolved solids to be estimated accurately.
The period of record at site 69 was divided into a
preintervention period (1942-62) and a postintervention
period (1966-80) (table 4), based on the principal filling of
Lake Powell. Annual step-trend analyses indicated a signifi-
cant decrease in annual streamflow of 2,705,000 acre-ft and
a highly significant decrease in annual dissolved-solids load
of 1,588,000 tons between the two periods. These decreases
represent a 24-percent change from the preintervention
median streamflow and a 19-percent change from the pre-
intervention median load. Dissolved-solids concentration did
not change significantly, which indicates that the changes in
streamflow and load were merely the result of increasing
storage in the reservoir. Monthly step trends indicate a
decrease in seasonal variability (fig. 26). Dissolved-solids
concentration decreased by as much as 600 mg/L during the
56 Characteristics and Trends of Streamflow and Dissolved Solids in the Colorado River Basin