U.S. Department of the Interior

U.S. Geological Survey

Implications of Lower Lake Powell Elevations and/or 

Annual Releases for Grand Canyon Resources

Charles Yackulic, US Geological Survey, Southwest Biological Science Center, Grand Canyon 

Monitoring and Research Center 

(with lots of help)

This information is preliminary and is subject to revision. It is being provided to meet the need for timely best science. 

The information is provided on the condition that neither the U.S. Geological Survey nor the U.S. Government shall be 

held liable for any damages resulting from the authorized or unauthorized use of the information.
Outline

 The Millennium drought from a Grand Canyon 

perspective

 Changing paradigm for Grand Canyon 

management

 A few scenarios

 Discussion
Emphasis has been on the long-term imbalance in the Lake Powell ledger. 

As we manage at lower elevations, we will increasingly be exposed to the 

impact of the substantial interannual variability in inflows.

Source: https://www.usbr.gov/rsvrWater/HistoricalApp.html
Flow variability at different time scales – comparing 

inflows and releases in recent history

 Sub-daily – more variation in releases

 Monthly – more variation in inflows

 Annual – more variation in inflows
Natural flows and inflows both vary more by month 

than releases (and have different seasonal patterns).

Source: https://www.usbr.gov/rsvrWater/HistoricalApp.html
Outline

 The Millennium drought from a Grand Canyon 

perspective

 Changing paradigm for Grand Canyon 

management

 A few scenarios

 Discussion
LTEMP provides an explicit guide for monthly volumes when annual 

volumes are 7.0 maf or greater. Below 4.9 maf, unable to meet day and 

night-time minimums discharges

Source: https://www.usbr.gov/rsvrWater/HistoricalApp.html
How did we get to these monthly volumes? 

Source: https://www.usbr.gov/rsvrWater/HistoricalApp.html
Do these monthly patterns still make sense?

 If below 3490, 

 Hydropower can’t be generated.

 High flow events aren’t possible.

 If releasing lower volumes,

 Overall sand export is much lower.

 Less variable flows likely to accelerate vegetation 

encroachment & likely to facilitate nonnative fish invasion.
Theory suggests nonnatives like smallmouth bass and green 

sunfish will be favored by predictable flows with minimal 

seasonal variation (if temperatures are also suitable).

Mims and Olden 2012, Adapted from Winemiller and Rose 2005
And smallmouth bass data from the Green and Yampa 

River supports this theory

(Bruckerhoff et al., in prep; Preliminary, subject to change, do not cite)
Outline

 The Millennium drought from a Grand Canyon 

perspective

 Changing paradigm for Grand Canyon 

management

 A few scenarios

 Discussion
Remember this slide

Source: https://www.usbr.gov/rsvrWater/HistoricalApp.html
Still able to shape monthly flows at low annual volumes 

if relax minimums and elevations not too low

(Preliminary, subject to change, do not cite)
But near dead pool (e.g., 3400) monthly allocations are 

driven by interaction between infrastructure and elevations.

(Preliminary, subject to change, do not cite)
Acknowledgements

 Lucas Bair

 Lindsey Bruckerhoff

 Bridget Deemer

 Drew Eppehimer

 Jack Schmidt

 Jian Wang

 Natural Flows metric group
Discussion

(Preliminary, subject to change, do not cite)