U.S. Department of the Interior

U.S. Geological Survey

Predicting Water Quality in Lake 

Powell: Updates and Improvements 

to the Existing Mechanistic Model

Bryce A. Mihalevich1, Bridget Deemer1, Charles B. Yackulic1

1U.S. Geological Survey, Southwest Biological Science Center, Grand Canyon Monitoring & 

Research Center, Flagstaff, Arizona

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."

bmihalevich@usgs.gov
U.S. Department of the Interior

U.S. Geological Survey

Lake Powell Appendix

Project Elements and Objectives

• USGS Ecosystems Mission Area “Forecasting Fish Population Responses to Drought”

• Special statement of work: “Leveraging Existing Data and Improving Existing Models 

to Better Bound Possible Water Quality Futures for Lake Powell and Its Tailwater” 

• Lake Powell Water Quality Monitoring Program

Funding amount and sources: 

• $100k (USGS Ecosystems Mission Area over 2 years) 

• $60k (BOR Statement of Work-AMWG Directive)

• $200k (BOR Interagency Agreement)

Cooperators: Bureau of Reclamation

LTEMP Resource goals: Natural Processes
What is CE-QUAL-W2?

• 2D (laterally averaged) 

hydrodynamic model

• Individual heat and constituent 

fluxes

• Simulates stratification and 

seasonal turnover

• Ability to specify GCD 

characteristics

• Penstock and Bypass elevations

• Used in BOR’s 24-Month Study’s
Model Updates

• 1. Incorporate new bathymetry data

• Match the volume-elevation curve used by BOR’s CRSS

• Represents ~7% loss in storage from last bathymetry dataset

Glen Canyon Dam

Jones and Root, 2021
Model Updates

• 2. Increased vertical and

longitudinal resolutions (mainly in

mainstem) • Improves numerical stability • Better represents physical features

Current New

Cell Depth (m) 1.75 1.00

Avg Cell Length (km) ~ 5.8 ~ 2.5

Min Cell (km)

2 1.5

Max Cell Length (km) 17.4 4.75

"Preliminary Information-Subject to 

Revision. Not for Citation or Distribution." New Flow

Current
Model Updates

• 3. Improve spatial representation

• More side branches (less volume in the mainstem)

Added branches

Current New

"Preliminary Information-Subject to Revision. Not for Citation or Distribution."
Model Testing

• Long-term historical model run (2010-present)

• Calibrate model under variety of conditions

• Increases confidence in forecasting applications

• Shows that we are predicting – not propagating
Model Inputs 

• Inflows

• Discharge

• Temperature

• Constituents (TDS) 

• Outflows

• Penstock and Bypass Releas

• Weather

• Air Temperature

• Dew Point Temperature

• Solar Radiation

• Wind Speed/Direction

• Cloud Cover

Colorado River

San Juan River

All Inflows have flow, 

temperature, and TDS

Dirty Devil River

Escalante River

e

ases

Most branches/tributaries 

do not have data

Glen Canyon Dam Rele
Model Inputs (cont’d)

• Wind Sheltering

• Based on available weather data

• Visitor use data used as surrogat

for boat traffic mixing (NPS, 2022

• Shading

• Segment specific 

• Calculated assuming 3600 ft 

(Mihalevich, 2020)

• Light extinction

• Based on long-term lake-wide 

secchi depth data (Deemer et al, 

2023)

Colorado River

San Juan River

All Inflows have flow, 

temperature, and TDS

Dirty Devil River

Escalante River

e 

)

s

Most branches/tributaries 

do not have data

Glen Canyon Dam Release
Model Inputs (cont’d)

• Initial Conditions (Starting value of each model cell)

Measured Profiles

January 2018

Measured profiles from Deamer et al. (2023)
Model Inputs (cont’d)

• Initial Conditions (Starting value of each model cell)

Measured Profiles

Interpolated Cells

January 2018

Measured profiles from Deamer et al. (2023)
Preliminary Results March 2021 – September 2022

"Preliminary Information-Subject to Revision. Not for Citation or 

Distribution." Measured profiles from Deamer et al. (2023)
Preliminary Results Cont’d

"Preliminary Information-Subject to Revision. Not for Citation or 

Distribution." Measured profiles from Deamer et al. (2023)

Model started in 2010

September 19-21, 2022
Preliminary Results Cont’d

Model started in 2010

September 19-21, 2022

"Preliminary Information-Subject to Revision. Not for Citation or 

Distribution." Measured profiles from Deamer et al. (2023)
Next Steps

• Install weather stations on Powell

• Validate input weather data

• Improve wind sheltering inputs

Rainfall

Air Temperature Solar Radiation

Wind Direction

Relative Humidity

Dew Point Temperature

Wind Speed
Next Steps Cont’d

• Continued model calibration

• Include more constituents

• Dissolved oxygen, pH, nutrients (P, N)

• Transfer updated version to BOR

• Predictions under specific scenarios
Acknowledgments 

• Many contributors to the long-term water quality monitoring program including Robert 

Radtke, Nick Voichick, Tom Sabol, Caitlin Andrews, Alex Walker, and Dean Sedgwick.

• Mentors that have provided model guidance including Scott Wells and Bethany Nielsen

References • Cole, T. M., & Wells, S. A. (2021). CE-QUAL-W2—A two- dimensional, laterally averaged, hydrodynamic and water quality model, Version 4.5. 

Department of Civil and Environmental Engineering, Portland State University

• Deemer, B. R., Andrews, C. M., Strock, K. E., Voichick, N., Hensleigh, J., Beaver, J. R., Radtke, R. (2023). Over half a century record of limnology 

data from Lake Powell, desert southwest United States: From reservoir filling to present day (1964-2021). Limnology and Oceanography Letters 

2023. https://doi.org/10.1002/lol2.10310

• Jones, D. K., Root, C., (2021). Modified topobathymetric elevation data for Lake Powell. Utah Water Science Center. Data Release. 

https://doi.org/10.5066/P9H60YCF

• Mihalevich, B. A., Neilson, B. T., Buahin, C. A., Yackulic, C. B., & Schmidt, J. C. (2020). Water temperature controls for regulated canyon‐bound 

rivers. Water Resources Research, 1–24. https://doi.org/10.1029/2020wr027566

• National Park Service (NPS), (2022). Glen Canyon NRA recreation visits by month. National Park Service Visitor Use Statistics. 

https://irma.nps.gov/Stats/SSRSReports/Park%20Specific%20Reports/Visitation%20by%20Month?Park=GLCA