Potential LTEMP Experiments

Fall - Water Year 2022

Technical Work Group Meeting

October 14, 2021

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Michael Moran

US Geological Survey

Lee Traynham

US Bureau of Reclamation
Purpose for HFE’s in the LTEMP

LTEMP Goal for sediment:

• “Increase and retain fine sediment volume, area, and 

distribution in the Glen, Marble, and Grand Canyon reaches above the elevation of the average base flow for ecological, 

cultural, and recreational purposes.”

LTEMP Alternative:

• “Alternative D includes spring and fall HFEs, which are 

intended to occur frequently to maintain and improve beaches, sandbars, and associated habitat.“

Science question from HFE Protocol:

• “Can sandbar building during HFEs exceed sandbar erosion 

during periods between HFEs, such that sandbar size can be 

increased and maintained over several years?”
Current conditions: many sandbar camps 

eroded by summer 2021 thunderstorms

Upper Blacktail camp 

(photo: Ben Reeder)

Upper 220-mile camp 

(photo: anonymous)

Tatahatso camp 

(photo: Ben Reeder)
Paria River Discharge & Sand Inputs

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USGS Preliminary Data, 2021. Do Not Cite. 

(https://www.gcmrc.gov/discharge_qw_sediment/station/GCDAMP/09382000# )

Jul 1, 2021 – Oct 12, 2021

Cumulative Sand Load ≅ 1,339,000 ± 20%
Upper Marble Canyon Sand Mass Balance

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USGS Preliminary Data, 2021. Do Not Cite. 

(https://www.gcmrc.gov/discharge_qw_sediment/reach/GCDAMP/09380000/09383050#)

Jul 1, 2021 – Sep 16, 2021

Zero Bias Value ≅ 1,200,000

Lower Uncertainty Bound ≅ 870,000
Lower Marble Canyon Sand Mass Balance

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USGS Preliminary Data, 2021. Do Not Cite. 

(https://www.gcmrc.gov/discharge_qw_sediment/reach/GCDAMP/09383050/09383100#)

Jul 1, 2021 – Sep 16, 2021

Zero Bias Value ≅ 150,000

Lower Uncertainty Bound ≅ 110,000
Fall High Flow Experiment

• Hydrograph characteristics

o Implement in early November (11/1)

o Peak release: ~33,900 cfs (6 hydro units, 4 bypass tubes)

o Peak release duration: from 1 hr up to 192 hrs (8 days) 

o Ramp rates: 4,000 cfs/hr up; 2,500 cfs/hr down

• Resource Considerations

o LTEMP resource evaluation

• Hydrograph Alternatives

o 192-hour extended duration

o 96-hour 

o 60-hour

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Resource Considerations 

1. Water quality and water delivery

2. Humpback Chub

3. Sediment

4. Riparian Ecosystems

5. Historic properties and traditional cultural properties

6. Tribal Concerns

7. Hydropower production and WAPA’s assessment of the 

status of the Basin Fund

8. Rainbow Trout Fishery

9. Recreation

10. Other Resources

Reference: 2016 LTEMP ROD, p. B-8,

Section 1.3 Implementation Process for Experiments Under Alternative D

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Fall HFE Hydrograph Alternatives 

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Fall HFE 

Hydrograph 

Alternatives

Water Release Pool Elevation2

Relative 

Impact to 

Basin Fund

November Total 

Release Volume 

(kaf)

Bypass 

Volume (kaf)

End of November 

Elevation (ft)

Number of 

Additional Days 

below 3525 ft

WY 2022 Minimum (ft)

Difference from No 

Action

No HFE 500 0

3540.70

0 3518.58 

-- --

60-hr HFE 

(MAM)3 634 82 3538.85

(1.85) 15 3517.89 

(0.69) $(1.30M)

60-hr HFE 

(DJF)3 634 82 3538.85

(1.85) 0 3518.58 

-- $(3.04M)

96-hr HFE 

(MAM) 710 126 3537.79

(2.91) 20 3517.50 

(1.08) $(1.94M)

96-hr HFE

(DJF) 710 126 3537.79

(2.91) 0 3518.59 

0.01 $(4.66M)

192-hr HFE 

(MAM) 915 245 3534.92

(5.78) 34 3515.42 

(3.16) $(3.70M)

1 – Peak capacity for all alternatives is 33,900 cfs.

2 – Assumes most probable hydrology as indicated in the September 24 Month Study. 

3 – Refers to the months in which less water would be released in order to balance a November HFE: March, April, May (MAM) or December, January, February (DJF).
Predicted results: sandbar model run with 96-hr 

HFE in fall 2021

*Current sandbar size estimated from model and will be measured in October, 

2021. The Mueller and Grams (2021) model predicts sandbar response for narrow 

reattachment bars (the “group 1a” sites of Mueller et al., 2018). It was calibrated 

using data from 9 narrow reattachment bars located throughout Marble and 

Grand Canyon. Other sandbar types tend to be less responsive.

Sandbar size in 

2022 with Fall 

2021 HFE

Sandbar size in 2022 

without Fall 2021 HFE

Sandbar size in 

Sept. 2021*

Based on Mueller and Grams (2021); Preliminary results, subject to review, do not cite
Predicted sandbar volume in April 2022 relative to 

October 2021 for the four HFE scenarios

Event Expected sandbar size 

immediately after HFE

Expected sandbar size in 

April 2022

192-hr HFE + 75% + 50%

96-hr HFE + 45% + 30%

60-hr HFE + 30% + 20%

No HFE + 0% - 10%

Based on Mueller and Grams (2021); Preliminary results, subject to review, do not cite
Native and Non-native Fish

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Although the best available science indicates a fall HFE may 

result in small benefits to undesired non-native species, these 

effects were highly uncertain (see rainbow trout section below) 

or the marginal impact was expected to be small (see brown 

trout section). Thus, expert opinion among fishery biologists 

was that a 60 hour fall HFE would not substantively increase 

risk to endangered and native fishes in Grand Canyon above 

the existing level of risk.

Reference: Page 3, Final Recommendation Regarding a Fall 

2021 High Flow Experiment (HFE) at Glen Canyon Dam, 

November 2021 
By consensus, the PI Team is opposed to recommending that the 

Department implement a 192-hour extended duration HFE in fall 

2021. 

Recommendation

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Technical representatives were divided in the assessment of a 

shorter duration 60-hour HFE, having evaluated the alternative 

for its ability to reduce negative resource impacts while still 

providing sufficient benefit to the sediment resource in terms of 

learning and effectiveness. The majority of representatives on the 

PI Team are opposed to recommending that the Department 

implement a 60-hour HFE this fall, several members support 

recommending that the Department implement a 60-hour 

duration HFE this fall, and two members have abstained from 

making a recommendation.
DOI Decision: No Fall HFE in 2021 

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•Decision Memo issued Oct 5, 2021

•Key Points 

o Assessment of Resources

• Positive: Sediment 

• Negative: Pool Elevation, Basin Fund 

o Unprecedented Drought Conditions 

• Drought Response Operations: ongoing releases from Initial Units

• Additional action may be necessary to protect critical levels

• Basin Fund support: deferred maintenance, a proposed rate 

increase, a one-time pursuit of appropriations for environmental 

program base funding. 

o Lack of consensus to implement 

HFE References

• LTEMP ROD - HFE Protocol (Attachment C)

• Science & Modeling References 

o HFE Sediment Modeling

o January 2020 – Changes in Sandbars and Campsites 

during HFE Protocol

o January 2020 - Effects of Dam Releases on in-channel 

sediment storage and sandbar dynamics

• 2018 Planning Team Report and Recommendation

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Summary of 

Past HFEs

https://www.usbr.gov/uc/rm/gcdHFE/
Sand Budget Model Results 

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