U.S. Department of the Interior

U.S. Geological Survey

Big Flood, 

Small Flood, 

Spring Flood, 

Fall Flood: 

HFE timing affects food base response?

Ted Kennedy

Jeff Muehlbauer
Timeline

1963 1970 1980 1990 2010 present

Glen Canyon Dam 

closed

Scuds and trout introduced

at Lees Ferry

HFEs

2000

New Zealand 

Mudsnail arrive Quagga arrive

Timeframe of this talk

Lake Powell fills

Dam operations

restricted

Floods

Most recent

Spring HFE

Warmest water

Since 1973

2007--

2012--

Duration of food base monitoring data

2013--

1990-2002, 06-09

2010--

Unpublished data, 

subject to change, 

do not cite
HFE Results from Glen Canyon
Mudsnails

usurping

lots of energy

Midges and 

blackflies key 

prey items for 

trout

Midges and 

blackflies only 

aquatic insects 

present

Pre-HFE 

From Cross and others, 

2011, Ec. App.

Lees Ferry Food Web
http://www.gcmrc.gov/discharge_qw_sediment/station/GCDAMP/09380000

Pre-HFE Post-HFE 

HFE released in March 2008
Mudsnails, 

worms declined

Midges and 

blackflies 

increased

Trout growth and 

numbers 

increased

Pre-HFE 

Post-HFE 

From Cross and 

others, 2011, 

Ec. App.

2008 Spring HFE Enhanced the Prey 

Base
Kennedy and others, 2014

Freshwater Biology

CC ∝ QQff BBgg

Drift is proxy for benthic
Spring HFE

Unpublished data, 

subject to change, 

do not cite

Top row: palatable, high quality prey

Bottom row: inedible, low quality prey

Spring HFE enhanced Prey Base
Drift measurements

(12 years, >300 different days)

Lees Ferry Drift Monitoring

http://www.gcmrc.gov/discharge_qw_sediment/station/GCDAMP/09380000

Drift Period of Record
Spring HFE

Fall HFE

Unpublished data, 

subject to change, 

do not cite

Top row: palatable, high quality prey

Bottom row: inedible, low quality prey

Fall HFEs +/- haven’t improved prey base
Data only available

Starting in 

• 2010(algae) 

• 2012 (light traps)

Unpublished data, 

subject to change, 

do not cite

Canyon-wide results
Distance from dam (km)

Kennedy et al. 2016 

BioScience

Citizen science emergence monitoring in 

Grand Canyon (2012-2018)
Fall HFE

Unpublished data, subject to change, do not cite

Fall HFEs +/- haven’t improved prey base
HFEs and Algae Production
Average Production 

One Month Pre-HFE (g O2m-2d-1)

Years w/ HFEs

Year w/o HFE

• 2010-present

Average Production 

One Month Post

-HFE (g O

m

2

-2

d-1

)

Data courtesy of 

Bridget Deemer, 

USGS

Unpublished data, 

subject to change, 

do not cite

Fall HFEs reduce algae production
• National Synthesis conducted by 

USGS-NAWQA

• Analyzed link between 

Flows alteration and Prey 

Base at 682 sites in US

Carlisle, D. M., Grantham, T. E., Eng, K., & Wolock, D. M. 

(2017). Biological relevance of streamflow metrics: regional 

and national perspectives. Freshwater Science, 36(4), 927-

940.

Stepping outside of Grand Canyon
“Impaired invertebrate communities were associated with 

depleted high flow magnitude, a result that corroborates 

theory...and a large body of case studies showing that depleted 

high flows are detrimental to aquatic species.” 

“However, the apparent nationwide importance of high flows 

in spring (March, April, May) also indicates that the timing (not 

just magnitude) of high flows is critical.”

From: Carlisle, D. M., Grantham, T. E., Eng, K., & Wolock, D. M. (2017). Biological relevance of streamflow 

metrics: regional and national perspectives. Freshwater Science, 36(4), 927-940.

Spring Floods Improve Prey Base
“Swelling stream flow....in the spring is an 

important life-history cue for most aquatic 

species in temperate climates.”

From: Carlisle, D. M., Grantham, T. E., Eng, K., & Wolock, D. M. (2017). Biological relevance of streamflow 

metrics: regional and national perspectives. Freshwater Science, 36(4), 927-940.

Floods are Important Life-History Cue
Month

Spring HFE

Fall HFE

Spring HFE

Fall HFE

Drift concentration (#·m-3

)

Unpublished data, 

subject to change, 

do not cite

• Data represent average drift concentration by month over period of record (2007-2018)

• HFEs in spring align favorably with life history timing of midges (a palatable, high quality prey item)

• HFEs in fall align favorably with life history timing of mudsnails (an inedible, low quality prey item)

Invertebrate life history timing
 Spring HFEs (n=2) infrequent compared to Fall 

HFEs (n = 6). 

 Most recent Spring HFE was >10 years ago, 

which pre-dates most food base datasets

 Hard to draw inferences about Spring HFEs

 Nevertheless, 2008 Spring HFE appeared to 

improve food base

Unpublished data, 

subject to change, 

do not cite

Conclusion
 Fall Disturbances (i.e., HFEs) don’t improve food 

base

 Key uncertainty: Will Spring disturbances 

improve food base in Glen and Grand Canyon?

 Test Benefits of Spring Disturbance

 Spring HFE 

and/or

 Spring Powerplant Flow 

Unpublished data, 

subject to change, 

do not cite

Next steps