Metalimnion low dissolved 

oxygen events in Lake Powell 

and their transport downstream 

of Glen Canyon Dam

Bridget Deemer

TWG Meeting 24 June 

2020

Grand Canyon Monitoring and Research Center

Southwest Biological Science Center

U.S. Department of the Interior

U.S. Geological Survey
Outline

 Background

 Low DO Events in Lake Powell

 Current Predictive Capacity

 Ongoing Work

2
Factors controlling dissolved oxygen in 

lake and reservoir bottom waters

warmer epilimnion

colder hypolimnion

Metalimnionthermocline

3
Factors controlling dissolved oxygen in 

lake and reservoir bottom waters, cont.

Nutrient loading from 

inlet water supports 

primary production

O2 O2 O O2 2

O2

O2

O O2 2

O2

O2 O2

O2

4
Factors controlling dissolved oxygen in 

lake and reservoir bottom waters, , cont. 2

Heterotrophic respiration 

of decaying organic 

matter creates anoxic 

conditions in the 

hypolimnion.

Gasp!

CO2 CO CO2 2

5

CO2

CO2 CO2

CO2 CO2

CO2

CO2

CO2 CO2
Factors controlling dissolved oxygen in 

lake and reservoir bottom waters, , cont. 3

Chemical oxygen 

demand can consume 

dissolved oxygen as 

suspended sediments 

undergo oxidation 

reactions.

6

FePO4

Gasp!

FePO4

FePO4

FePO4
Dissolved oxygen and trout

Unpublished data, subject to 7

change, do not cite.

 Temps <15C

 DO can be lethal

if <3 mg/L

 Temps >15C

 DO can be lethal 

if <5 mg/L

Slide courtesy of Ted Kennedy
Advection carries low DO from 

zones of high production/sediment 

to Glen Canyon Dam

8 Image from video courtesy of Robert Radtke
Lake Powell—August 22, 2019

Pocket of low dissolved

oxygen water above penstocks

(minimum DO = 3.2 mg/L) Unpublished data, subject to 9

change, do not cite.

~Penstock

depth
Lake Powell—October 8, 2019

Unpublished data, subject to 10

change, do not cite.

Pocket of low dissolved

oxygen water above penstocks

(minimum DO = 2.6 mg/L)

~Penstock

depth
Events typically occur in fall and are 

improved by mixing

As of 11 Oct 2019

Lake was mixing

 Temperatures falling

 Oxygen rising

Graph showing temperature

and dissolved oxygen for 

Colorado River below Glen

Canyon Dam

11

2019

2019

Slide modified from Ted Kennedy Unpublished data, subject to 

change, do not cite.

11 Oct

11 Oct
Dissolved oxygen increases 

downstream

Unpublished data, subject to 12

change, do not cite.

 Increase in maximum 

DO mostly owing to 

algae 

 Rule of thumb: Airwater gas exchange 

increases DO in Lees 

Ferry by ~0.04 mg/mile 

(Hall et al. 2012)

Same parcel

of water

Slide modified from Ted Kennedy
Summary of Low DO Affecting 

Downstream River in GCD System

 Several instances where low dissolved 

oxygen water reached the reservoir outflow 

causing concern for the GCD reach

 2003

 2005

 2014

 2019

13
Water Quality Knowledge 

Assessment

 Team: Bridget Deemer, Peggy Roefer, Todd Tietjen, 

Robert Radtke, Charles Yackulic

 Status and Trends:

 SIGNIFICANT CONCERN, UNKNOWN TREND: GCD 

outflow temperature and dissolved oxygen in support 

of Rainbow Trout

 GOOD CONDITION, INCREASING TREND: GCD 

outflow temperature in support of Humpback Chub

 SIGNIFICANT CONCERN, UNKNOWN TREND: GCD 

outflow phosphorus concentrations in support of 

ecosystem productivity

14
Lake Powell Dissolved Oxygen 

(2000-2020)

15

Plot Courtesy of Robert Radtke
Current Predictive Capacity

 DO module for CE-QUAL-W2 can predict low 

DO events, but does not always predict the 

concentrations at penstock height accurately

 We know these events are most likely to 

occur when the reservoir is low and we have 

a high inflow year

 Quarterly whole-lake trips and monthly trips 

to Lake Powell give us an idea of when a low 

DO event may be likely to reach the penstock 

depth

16
Sonde Directly Below Dam

 Data from 2015 forward available on the 

GCMRC Data Portal

 Nick Voichick is working to QA/QC back 

years

17
Current Progress in Realtime Sonde 

Connectivity

 Sonde at Lees Ferry currently transmitting 

data to Amazon Web Services

 Goal is to have data transmitting from the 

sonde directly below GCD soon

 Tim Andrews has sent an enclosure to BOR and is 

working with a duplicate to setup design

 BOR will be upgrading electrical outlet and 

installing the enclosure that Tim sent

 Final step will be attaching cellular antennae (1 or 

2 site visits from USGS)

18
19
Proposal in for USGS/NPS Water 

Quality Partnership Grant Program

 Modernizing water quality monitoring of the 

Colorado River in Glen Canyon, AZ

 Proposal would fund connectivity at 2 buoyed 

sites

 Technical Assistance Proposal

 1-2 year follow up potentially, up to $150,000

20
Map Courtesy of Tom Gushue 21