The HFE Page

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High-Flow Experimental (HFE) Releases

Construction and operation of dams results in numerous physical and ecological changes to river systems. Among them is the sediment carrying capacity of the river downstream of the dam. With the construction of Glen Canyon Dam, seasonal flooding that once moved sand from the riverbed to the shoreline, no longer occurs. Because more than 90 percent of the sediment that historically moved through the Grand Canyon is trapped behind the dam, the primary sources of new sand to the river system are two downstream tributaries: the Paria and Little Colorado rivers. The Operation of Glen Canyon Dam Final Environmental Impact Statement, completed in March 1995, hypothesized that controlled high-volume releases of water could be important for restoring ecological integrity downstream from the dam. Testing that hypothesis would help determine whether experimental high flows could be used to benefit important physical and biological resources in Grand Canyon National Park and Glen Canyon National Recreation Area. Such flows would also be consistent with the objectives of the Grand Canyon Protection Act of 1992. Because controlled experimental high-flow releases to some extent mimic natural flooding, conducting such releases would provide the opportunity to evaluate the potential benefit to sediment-dependent resources including sandbars and camping beaches, marsh and riverside vegetation, and backwaters, which are near-shore areas of low-velocity flow which may be used as rearing habitat by native fish.

In May 2012, the Department of the Interior implemented a new protocol for conducting multiple high-flow experimental releases through 2020, built on the 16 years of knowledge gained from prior HFEs and associated scientific research and experimentation conducted under the Adaptive management Program. The protocol provides a flexible framework to conduct HFE releases when favorable sediment conditions exist so the optimal timing, duration, frequency, and other conditions that will maximize ecological and riparian benefits downstream in Grand Canyon can be determined. The protocol identifies the conditions under which an HFE release will likely yield the greatest conservation and beneficial use of sediment deposited by inflows from Colorado River tributaries as a result of rainstorms, monsoons, and snowmelt.

The ultimate goal of understanding the complexities of the interrelated ecosystem downstream of Glen Canyon Dam is a long-term challenge. The adaptive management model which emphasizes an ongoing cycle of learning through experimentation, refinement, and improvement over time, provides the appropriate framework to achieve this understanding. Through the Glen Canyon Dam Adaptive Management Program, continued implementation of HFEs as a key operational strategy will yield invaluable knowledge about the response of, and benefit to downstream resources. [1]

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Links and Information

2011 HFE Protocol EA

LTEMP Experimental Action: Sediment-Related Experimental Treatments (BA, pages 24-30) [6]

Spring and fall HFEs would be implemented when triggered, based on the estimated sand mass balance resulting from Paria River sediment inputs during the spring and fall accounting periods, to rebuild sandbars. These HFEs include sediment-triggered HFEs in spring or fall HFEs in May-Apr and Oct-Nov, proactive spring HFEs as triggered by high annual release volume (> 10 maf) in May-Jun, and extended duration (>96 hr) fall HFEs in Oct-Nov.

  • Sediment-Triggered Spring HFEs after the first 2 years of LTEMP (beginning in spring of 2020)
  • Proactive Spring HFEs in years with high annual water volume (i.e., ≥10 maf) in April, May, or June (the duration is limited to 24 hours) and like other Spring HFEs wouldn't begin until spring of 2020
  • Sediment-Triggered Fall HFEs up to 96 hours
  • Extended-Duration Fall HFEs up to 250 hours (the duration of the first implementation of an extended-duration HFE will be limited to no more than 192 hours and there will be no more than four extended-duration fall HFEs over the 20-year LTEMP period)

Glen Canyon Dam Flow Experiments

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Presentations and Papers











2015 HFE Synthesis Workshop

Other Stuff

Calculating the Cumulative Sand Load for an HFE

  1. Determine the amount of sand that has come in from the Paria River during the HFE Accounting Period you are interested in. Go to the Paria River gage at Lees Ferry and check the Cumulative Sand Load box and enter the dates of the HFE Accounting Period.
  2. Determine the amount of sand that has been transported out of Marble Canyon during the HFE accounting period by taking the lower bound value of the change in sand storage in Lower Marble Canyon and subtracting it from the lower bound value of the change in sand storage in Upper Marble Canyon.
  3. Subtract the amount of sand that has been transported out of Marble Canyon from the amount of sand that has come in from the Paria River and you get the amount of sand Reclamation uses for planning the HFE.

Calculating Magnitude and Duration of an HFE

Reclamation takes the amount of sand calculated above and subtracts the amount of sand that will be transported out of Marble Canyon between the time of the model run and the HFE. Reclamation then calculates the largest possible volume and duration release from the dam using the Scott Wright sediment transport model that does not result in a negative sand balance between the 30-mile gage and the LCR by the end of the accounting period.

How much water can be released at Glen Canyon Dam?

  • 8 generators = 4,000 cfs each = 32,000 cfs
    (note that there is usually one or two generators down for maintenance at any given time)
  • 3 bypass tubes = 5,000 cfs each = 15,000 cfs
  • 2 spillways (require reservoir elevations above 3648') = up to 208,000 cfs

How often would an HFE be triggered? (LTEMP Appendix P)

  • Proactive Spring HFEs: 10% of years
  • Sediment-triggered Spring HFEs: 26% of years
  • Sediment-triggered Fall HFEs: 77% of years
  • Extended-Duration Fall HFEs: 25% of years