Lake Powell Animation: 1965 to 2006
Susan Hueftle
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| Clicking image opens animation -- .gif format (5.7 MB) |
This animation sequence summarizes a 36 year history of data collection on Lake Powell. These isopleths, or 3-D contour plots, show the dynamics of specific conductivity (a measure of the salinity or dissolved chemicals found in water) in the main channel of Lake Powell.
The hydrodynamics seen in these isopleths are dominated by the inflows of the Colorado River, depicted here entering from the upper right side of the plot. In the winter, density currents of cold, more saline water (dark orange to brown) can be identified moving along the bottom of the lake when the river base flow is denser than the surrounding lake water. In the spring, the relatively fresh snowmelt from the river inflows (light blue) moves or floats across the surface of the lake, since it is warmer and more dilute (hence lighter) than the rest of the reservoir. Spring represents the period of greatest volume input to the lake. As summer proceeds, the river volume decreases and its temperature and salinity increases (a result of higher ion dissolution from irrigation return flows, higher temperatures and hence higher solubility). When this increasingly saline (brown-colored) plug of water cools in late summer, it eventually reaches a density where it sinks and once again moves along the bottom of the former Colorado River's channel.
Glen Canyon Dam is located at the left hand side of the plot, with the elevations of the penstocks, spillways, and river outlet works (jet tubes) indicated by arrows when each is in operation. Water is continuously discharged through the penstocks, passing through the turbines to generate power. Discharges through the spillways (near the surface) and river outlets (below the penstocks) bypass the powerplant, and have therefore been used rarely. Such uses did occur on several unusual occasions. In 1965 and 1966 water was released through the jet tubes to compensate for water lost to Lake Mead during Lake Powell's filling. In the mid-1980's, extremely large water inflows filled the reservoir and consequently both the spillways and jet tubes were utilized to draw down the reservoir. Most recently, the jet tubes were used in an experimental test flow in spring of 1996 to simulate higher spring flood flows.
Decadal climatic patterns of drought and flood are manifested in the overall salinity of the reservoir as well as the level of the lake. A drought, as seen in the mid 60's, late 1970's (particularly 1977), and late 80's to early 90's shows diminishing lake elevations and conductivity values from 800-1200 µS/ cm (orange to brown colors on plot). Wet periods, such as late 60's, early to mid 80's and mid 90's, demonstrate higher lake levels and fresher, more dilute salinity, as well as increased use of alternate release structures.
As you run the animation sequence, you can see how the flow through the reservoir is drawn down and through the penstocks during the winter months, and how the spring inflows are drawn across the surface of the lake, mixed downward in the fall, and moved out the penstocks.
Variations in the 36 year history of sampling Lake Powell included changing protocols. The animation sequence most effectively conveys the processes occurring in the reservoir from 1971 to 1982, when lake wide sampling trips occurred on a monthly basis. Quarterly lake wide sampling occurred in the 1960's and 1990's to the present, while sampling from 1982 to 1991 dwindled from 6 to 1 trip per year. This reduced sampling scheme precludes visualization of seasonal processes and hindered interpretation of this historically unique and significant period. The length of time each plot is shown roughly relates to the sampling periodicity, i.e., monthly sampling plots are displayed faster than annual samplings.
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Lake Powell Animation -- .gif format (5.7 MB)
If you have questions, please contact:
Susan J. Hueftle
Grand Canyon Monitoring & Research Center
2255 N. Gemini Dr.
Flagstaff, AZ 86001-1600
Phone: 928.556.7460
shueftle@usgs.gov