U.S. Department of the Interior

U.S. Geological Survey

Discussion of the Bug Flows Synthesis and Review 

& 

Opportunities for Spring and Summer Flow 

Experiments

Ted Kennedy1

1-US Geological Survey, Southwest Biological 

Science Center, Grand Canyon Monitoring and 

Research Center, Flagstaff, AZ
Why Bug Flows?

~80% of aquatic insects

have cementing egg laying

strategies that are 

vulnerable to artificial tides

Year-round hydropower 

fluctuations do not support 

natural processes essential to 

diverse and resilient 

invertebrate assemblages

Photos of aquatic insects (top) and eggs cemented on various substrates (bottom).

From Miller and others 2020, Freshwater Science

From Kennedy and others 2016, Bioscience
Why Bug Flows?

 Daily hydropower fluctuations 

create “tides”

 Insects lay eggs at water line at 

dusk

 When tide drops, eggs dry, die

Bug Flows seeks to 

mitigate this

From Kennedy and others 2016, Bioscience
What is a Bug Flow?

 Give bugs the weekends off

 Weekend stable low flows from May-August

 34-36 days/years

 Tested 2018-2020

 Eggs laid on weekends never dry

https://waterdata.usgs.gov/az/nwis/uv?site_no=09380000

May-August

Unpublished data, 

subject to change, do 

not cite.
Goals of Bug Flows

 Proximate Objective

 Improve egg laying 

conditions for aquatic 

insects

 Ultimate Objective

 “Improve food base 

productivity and 

abundance or diversity 

of mayflies, stoneflies, 

and caddisflies”

Table 4, LTEMP EIS

From Attachment B: Table 4, p. B-14, LTEMP-Record of Decision
Bug Flows-Key Findings

 Enhanced natural processes 

and improved food base

 More egg laying substrates

 More insect emergence

 More caddisflies (but not midges)

 More GPP

 Condition of native fish & humpback 

chub positively related to GPP

 Enhanced rainbow trout fishery

 Higher catch rates

Unpublished data, 

subject to change, do 

not cite.
Science Advisor Review

Timeline

 October 12-GCMRC submits Bug Flow report

 October 28-Bug Flow workshop #1

 November 4-Bug Flow workshop #2

 January 4-Science Advisor review received

 January 11-ARM presentation w/ 2021 light trap data

 January 13-TWG meeting (today)
Take Homes from Science Advisors

 Bug Flows was successful

 Ruhi: “...Bug Flows were successful, overall, in enhancing natural 

processes...”

 Downes: “Experiment successfully met proximate and ultimate 

objectives”

 Kroll: “...high likelihood the experiment has worked...”

 Colvin: “The Bug Flows are meeting primary and proximate 

objectives and the science being conducted is cutting edge.”
Take Homes from Science Advisors

 Report should include more details

 More statistics 

 Include summary table 

 Better link to hypotheses and objectives

 Separate direct vs. indirect effects

Michael Colvin

Albert Ruhi

Barbara Downes
Take Homes from Science Advisors

 More analyses and modeling would be informative

 Dynamic ecosystem models

 Species-level analysis of abundance

 Trait analysis

Michael Colvin

Albert Ruhi

Barbara Downes

Stephanie Kroll
Take Homes from Science Advisors

 Thoughts about Future Experiments

 Add months 

 Shifting months could be informative

 Opportunity cost of changing design 

Barbara Downes

Albert Ruhi

Stephanie Kroll
Take Homes from Science Advisors

 Quantifying environmental benefits

 Compensating hydropower

Albert Ruhi

Barbara Downes

Barbara Downes

Barbara Downes
Opportunities for Spring and Summer Flow 

Experiments

GCD Experimental Flow Duration Implementation 

Window

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

Fall HFE up to 96 hours October - November

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

2018, 2019, 2020

2004, 2012, 2013, 2014,

2016, 2018 (2015, 2021)

1996, 2008

Not yet tested

Not yet tested

Not yet tested

Testing Flow

Experiments

LTEMP Flow 

Experiments

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

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

* First test not to exceed 192 hours

** First test 24 hours

*** After first test, up to 250 hours

Spring or summer 

disturbance flow?

Preliminary data, do not 

cite.