River Resource Management in the Grand Canyon (1996) / Chapter Skim
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4 OPERATION OF GLEN CANYON DAM
4 OPERATION OF GLEN CANYON DAM
Pages 50-69
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From page 50... ...
for all of the operational rule alternatives considered (BOR, t994b, Table 11-7~. This chapter compares the hydrology of the Colorado River before and after construction of the Glen Canyon Dam, describes operating rules for the dam and their evolution, and provides an overview of water supply above the dam.
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From page 51... ...
Tributary Inflows Below the Dam Flows through the Grand Canyon are normally dominated by the water released from Glen Canyon Dam; tributaries belowthe dam such asthe Paria River, Little Colorado River, and Kanab Creek (Figure 1 .1 ) contribute less than
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From page 52... ...
10 12 FIGURE 4.1 Comparison of monthly average discharge at Lee's Ferry before and after closure of Glen Canyon Dam in 1963 SOURCE: Bureau of Reclamation (1994~. 2 percent of the average flow, as shown in Table 4.1.
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FIGURE 4.2 Example of fluctuations in stage height of the Colorado River prior to construction of Glen Canyon Dam (October 1928 through September 1929 at Colorado River near Grand Canyon gauge)
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From page 54... ...
Wave velocities following rapid increases in flow rate were also documented and were used to verify calibration of an unsteady flow simulation model (Smith and Wiele, 1993~. The flow rates shown in Tables 4.2 and 4.3 are from both the dye study and the flow simulation model.
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From page 55... ...
Operation of Glen Canyon Dam 55 TABLE 4.2 Travel Time and Velocities Through Grand Canyon with Daily Flows Varying from 3,000 to 26,000 cfs and Averaging 15,000 cfs Water Travel Time Wave Travel Time Days mph Days mph Location River Miles Lee's Ferry 0 0 0 Uttle Colorado 62 1.4 2.2 0.6 4.3 Phantom Ranch 88 2.0 2.2 0.8 4.6 National Canyon 166 3.7 2.2 1.3 5.3 Diamond Creek 225 4.4 2.2 1.8 5.2 SOURCE: Graf (1993)
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From page 56... ...
Monthly and Annual Releases The annual release target for Glen Canyon Dam has always been 8.23 million acre-feet. This amount satisfies the Law of the River (Chapter 3)
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From page 57... ...
These interim flow targets, which remained in effect as of September 1995, are: · daily maximum releases not more than 20,000 cfs; · minimum flows not lower than 5,000 cfs at night and 8,000 cfs during the day; · change in release rate not to exceed 5,000, 6,000 or 8,000 cfs per day as monthly release targets vary from <0.6, 0.6 to 0.8, and >0.8 mat, respectively; and ~ hourly changes in release rate not to exceed 2,500 cfs when increasing and 1,500 cfs when decreasing. These interim flow rules are intended to reduce the adverse effects of dam
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From page 58... ...
Experience with Interim Flows and Exception Criteria The changes in daily operating rules have had no effect on the ability of the BOR to meet monthly or annual release targets because monthly release targets are totally independent of interim flow rules. It is, however, now much more difficult for the Western Area Power Administration (\/VA PA)
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From page 59... ...
_ _ _ _ . _ 15 APR 95 16 APR 95 17 APR 95 18 APR 95 19 APR 95 Dam and lime FIGURE 4.5 Ramping rates for release of water from Glen Canyon Dam for 1 week in April 1995.
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From page 60... ...
was found to be much more important in terms of environmental impact than the up rate. The range of variations in monthly release targets results in the approximate ranges in allowable daily fluctuation shown in Table 4.5, which are much less than the theoretically allowable variation between maximum and minimum daily rates.
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From page 61... ...
BOR considers use of the spillway undesirable on a routine basis, because it is considered to have the shortest useful life of any of the components of the dam, even after being modified to prevent cavitation following the 1983 flood. WATER SUPPLY ABOVE THE DAM Water Balance in Lake Powell All predictions of future probabilities for release or spill of water from Glen Canyon Dam are based on assumptions that are inherent in the mass balance equations of the CRSM.
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From page 62... ...
Data on water balance over this interval should provide a way to improve the bank storage estimate. Mass balance estimation could be improved through an analysis of the data on flow and reservoir stage, including the recent drought period, combined with a corrected estimate of evaporation over the same period.
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From page 63... ...
in the number of years during which the annual release from the dam will be at the minimum level. Evaporation Loss Since the completion of Glen Canyon Dam, the Colorado River has reached the sea only during 2 years of unusually high runoff years (1983
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From page 64... ...
While this may provide a correct estimate of depletion caused by dam construction, it is much less than the evaporation that would be used in mass balance calculations for the river simulation model. Bawdy (1991)
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From page 65... ...
B-154~. For example, the figure indicates that 70 percent of the time water is expected to be above the bottom of the radial gates-which is the minimum elevation for controlled releases exceeding the turbine capacity (as necessary for an experimental flood or 50,000 cfs)
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From page 66... ...
This is 1 mat less than the previous target level. Reregulating Dam The conventional approach to mitigating the environmental effects of daily fluctuations below hydropower dams is to construct a small dam below the
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From page 67... ...
While the range between revised maximum and minimum allowable release rates is still quite large (5,000 to 25,000 cfs) , the possible daily fluctuations resulting from the preferred alternative rules are much less-5,000 to 8,000 cfs depending on the monthly release volume target.
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From page 68... ...
4. If the option to mitigate environmental effects of daily fluctuations below Glen Canyon Dam includes building a reregulation dam, a thorough analysis of its costs and possible environmental impacts should first be completed.
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From page 69... ...
1988. Salt Lake City Area, Analysis of Alternative Release Rates at Glen Canyon Dam.
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