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Last modified
1/26/2010 4:18:43 PM
Creation date
10/21/2007 11:22:57 AM
Metadata
Fields
Template:
Water Supply Protection
File Number
8220.101.10
Description
Colorado River Water Projects - Glen Canyon Dam-Lake Powell - Adaptive Management
State
CO
Basin
Colorado Mainstem
Date
10/27/1997
Author
Glen Canyon Dam TWG - Spike Flow Subgroup
Title
Report of the Spike Flow Subgroup - Glen Canyon Dam Technical Work Group - 10-27-97
Water Supply Pro - Doc Type
Report/Study
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<br />002552 <br /> <br />Some discussion aiso considered the conceDt that tlood [lows counteracted the possible "Qverse <br />impacts that t1ucruations had on beach erosion, thus rebuilding the deposits that would eventually <br />slough back into the eddies, regardless of the nature of the powerplant operations. Some <br />suggested that more frequent Hoods could allow higher levels of Huctuations. <br /> <br />Interpretation of Statute, the 1996 AOP Agreement, the GCDEIS ROD, and Risk <br /> <br />With this evolving positive view towards spills. a desire for a test of the GCDEIS Beach Habitat <br />Building Flow was expressed by the Transition Work Group beginning in 1994. This request for <br />a purposeful powerplant bypass was strongly opposed by the Basin States, claiming a violation <br />of the 1968 Colorado River Basin Project Act provision of avoiding anticipated spills. interpreted <br />as powerplant bypasses, This opposition created an impasse that blocked such a test. <br /> <br />Additional discussions between members of the Transition Work Group and the Basin States <br />resulted in a proposal for a modification of the GCDEIS preferred alternative. that of moving <br />Beach Habitat Building Flows (BHBF) from years oflow reservoir conditions (when spills <br />would not be required for hydrologic reasons) to years of high reservoir conditions and high <br />inflows. Thus a BHBF would occur in years when there was an expectation of having a <br />hydrologically induced spilL Since the researchers had targeted the March-April timeframe as <br />the preferred time for a BHBF. the water that would have been expected to spill in June or July <br />would be pre-released earlier in the year to accomplish the intent of the BHBF. Some <br />researchers had concerns about the magnitude of releases in temporally adjacent months of the <br />BHBF. citing the potential for high powerplant releases to negate the beach building gains made <br />during the BHBF. Long term sediment balance continued to be a concern, However, the <br />benefits of reaching a compromise solution outweighed these possible negative impacts and this <br />agreement was institutionalized in the 1996 Annual Operating Plan for the Colorado River, <br />signed by the Secretary of the Interior in December 1995. <br /> <br />The following March and April 1996, the requested test of the BHBF occurred with a release of <br />..5,000 cIs for a period of 7 days. This How included a powerplant bypass of about 15,000 cIs. <br />Such a release was not required for hydrologic reasons. but was allowed by the Basin States as a <br />one-time test as a result of the agreement contained in the 1996 AOP. <br /> <br />Ih December 1996, the GCDEIS Record of Decision was signed by the Secretary of the Interior <br />and included this modification of the preferred alternative. The BHBF negotiations did not <br />include an explicit discussion of the hydrologic situation that should trigger a BHBF. Some <br />recognition was given to the concept that this risk could be something less than the 50 percent <br />level produced by using the most probable forecast from the National Weather Service as the <br />inflow hydrology, but those discussions were left unresolved at the time of the signing of the <br />GCDEIS ROD. ,At the April 1997 BHBF symposiwn. the issues ofBHBF frequency, high <br />powerplant releases. and BHBF benefits were again raised, It is these issues of risk and <br />frequency,that the TW(hpill subgroup now addresses. <br /> <br />3 <br />
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