Potential Experiments and 

Management Actions

Water Year 2021

TWG Meeting

January 22, 2021
Objectives

•Introduce “menu” of LTEMP experiments for 

consideration in Calendar Year 2021.

•Discussion of Process: Planning and 

Implementation Team status for spring 2021 

considerations.

•Tee up GCMRC for more detailed discussion of 

these items.
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

Other Potential FY2021 Flows :

• Apron Repair + Spring Disturbance Flow Test (March)

• Release reduction for Overflight (steady 8,000 cfs for 7 days in May)
High Flow Experiment Timeline

Spring HFE, sediment triggered

• Sediment accounting: Dec 1 – June 30

• Implementation / Planning Team decision: late February

• Possible implementation: March-April

Spring HFE, proactive

• Equalization (GCD releases >= 10 maf)

• Planning Team: late February

• Possible implementation: April-June

Fall HFEs, sediment triggered

• Sediment accounting: July 1 – Nov 30

• Implementation / Planning Team: early September

• Possible implementation: October – November 
HFE Accounting & 

Implementation Windows
Macroinvertebrate Flows

“Bug Flows” Objective: Improve food base 

productivity and abundance or diversity of 

mayflies, stoneflies, and caddisflies

• “Give bugs the weekends 

off”

• Weekend stable low flows 

from May-August

• Eggs laid on week-ends

never dry

• Tech Team will consider a 

4th year soon
Trout Management Flows

TMFs are a special type of fluctuating flow designed 

to reduce the recruitment of trout by disadvantaging 

YOY trout

FIGURE 6 Example 

Implementation of a TwoCycle TMF in June and July 

with Resumption of 

Normal Fluctuations 

between Cycles and 

Afterward (Monitoring for 

effectiveness would occur 

before and after each 

cycle. The horizontal line 

below the graph shows 

periods of normal 

fluctuation [blue] and 

TMFs [orange].) 
Potential LTEMP Flow Experiments 

Spring 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

Other Potential FY2021 Flows :

• Apron Repair + Spring Disturbance Flow (March)

• Release reduction for Overflight (steady 8,000 cfs for 7 days in May)
Spring Disturbance Considerations

• Hydrograph characteristics:

o Implement in mid-March  March 15-26

o Minimum release: 4,000 cfs for 120 hours

o Peak release: ~19,400 cfs for 82 hours (6 hydro units)

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

8,000 cfs per 24-hour period
Spring Disturbance Flow - Tech Team Update

• Tribal Notification – Tuesday, January 12 

• Annual Reporting and TWG meetings to discuss 

potential exp. actions for the year - Today

• Implementation / Planning Team to develop a 

consensus recommendation to DOI

o AMWG / TWG webinar – 2pm MST Monday, January 25

o Technical Team Call # 4 & final report – January 28

o GCD Leadership Team – 11am MST Tuesday, February 2

• DOI Designee decision – COB Wednesday, February 3

• Possible implementation – Monday, March 15

10
Clarence Fullard

303-253-1042

cfullard@usbr.gov