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Potential LTEMP 

Experiments, Water Year 

2021, Fall 2020

October 14, 2020
Agenda

1. Background info

2. Current resource conditions 

3. Timeline and next steps 

4. Questions & discussion 

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2020 Possible Fall HFE: Why?

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Review of Problem: 

Sediment budget affected by disruption of sand 

supply and change in flow regime

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Sandbars and the sand mass 

balance on the Colorado River in 

Grand Canyon

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Sandbars

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Sandbars and the sand mass 

balance on the Colorado River in 

Grand Canyon 1

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Sandbars and the sand mass 

balance on the Colorado River in 

Grand Canyon 2
Sandbars and the sand mass 

balance on the Colorado River in 

Grand Canyon 3

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LTEMP Process for Experiments

• Annual Reporting and TWG meetings to discuss 

potential experimental actions for the year

• Tribal consultation

o Notification issued to Parties to the PA 9/24

• Work with Implementation / Planning Team to 

develop a consensus recommendation to DOI

o AMWG / TWG webinar

o GCD Leadership Team

• DOI decision and possible implementation

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Potential LTEMP Flow Experiments 

Water Year 2021

GCD Experimental Flow Duration Implementation 

Window

Fall HFE up to 96 hours October - November

Extended Duration Fall HFE 97- 192* or 97-250 hours*** October - November

Spring HFE∆ up to 96 hours March – April

Proactive Spring HFE∆◊ 24 hours** April – June

Trout Management Flows up to 3 cycles/month for 4 months May – August

Macroinvertebrate Flows target 2-3 replicates May – August

* First test not to exceed 192 hours

** First test 24 hours

*** After first test, up to 250 hours

∆ no Spring HFE in same WY as extended duration Fall HFE

◊ no proactive Spring HFE in same WY as sediment-driven Spring HFE
HFE Accounting & 

Implementation Windows

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Paria River Discharge & Sediment Inputs

USGS Preliminary Data, 2020. Do Not Cite. 

(https://www.gcmrc.gov/discharge_qw_sediment/station/GCDAMP/09382000# ) Oct. 7, 2020

Discharge

Paria River at Lees Ferry

(Jul 1, 2020 – Oct 13, 2020)

Cumulative Sand Load

Paria River at Lees Ferry

(Jul 1, 2020 – Oct 13, 2020)
Marble Canyon Sand Mass Balance

(July 1, 2020 – Sep 29, 2020)

Upper Marble Canyon

Zero Bias Value = -130,000

Lower Marble Canyon

Zero Bias Value = 10,000

USGS Preliminary Data, 2020. Do Not Cite. 

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

https://www.gcmrc.gov/discharge_qw_sediment/reach/GCDAMP/09383050/09383100) Oct. 7, 2020
Sand Budget Model Results

As of this week, not sufficient 

sediment to support an HFE.
Fall HFE Considerations (WY 2021)

• Hydrograph characteristics:

o Implement in early to mid-November (11/9)

o Peak release capacity: ~35,000 cfs (6 hydro units, 4 bypass tubes)

o Peak release duration: from 1 hr up to 96 hrs (4 days) 

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

• Resource Considerations 

o Basin Fund Status

o Non-native Fish

o Green Sunfish at RM -12, West GC

o Brown Trout at Lees Ferry

• Proposed Monitoring
Upcoming meetings

•October 2020

• Tech team call #4: last call to implement HFE.

• Oct 19-21: HFE Leadership Team Meeting, Department of 

Interior decision (if recommended by Tech Team).

• October 22: Notify GCDAMP and public.

• November 9: possible HFE start (if recommended).

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Summary and Next Steps

• Current sediment conditions DO NOT support a Fall HFE

• Final HFE Technical Team Call: Friday, October 16

o Verbal report out on resource status 

 Sediment, Basin Fund, Green Sunfish, Brown Trout, Other

o Public Affairs update re: notification strategy 

• Consultation meetings as needed (Basin States, Tribes)

• Additional steps if we move forward with an HFE

• Otherwise...

• 10/23 – Email AMWG/TWG w/ notification 

• 11/30 – Sediment modeling through accumulation period

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Clarence Fullard

303-253-1042

cfullard@usbr.gov
Maintenance Schedule WY2020

Glen Canyon Power Plant Planned Unit Outage 

Schedule for Water Year 2021

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