Improving the Lake Powell CEQUAL-W2 Water Quality Model 

Bryce A. Mihalevich1,2, Bridget R. Deemer2, Charles B. Yackulic2 

1U.S. Bureau of Reclamation, Interior Region 7 - Upper Colorado Basin, Salt Lake City, Utah 

2U.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." 

U.S. Department of the Interior 

U.S. Geological Survey bmihalevich@usbr.gov 
Recent Water Quality Trends 

Currently 3571 ft 

Glen Canyon Dam

"Preliminary 

InformationSubject to 

Revision. Not 

for Citation or 

Distribution." 
 

 

Wahweap Temperature Variability 

Sept. 2022 

Current Depth 

Summer 2023 

Higher SD = More 

difficult to predict 

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 Not for Citation or Distribution." 
 

 

 

 

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 
Updates from last year 

• New bathymetric data 

• Finer model grid 

• More branches/tributarie

Colorado River 

s 

San Juan River 

Glen Canyon Dam Releases 

Dirty Devil River 

Escalante River 

Flow Direction 
 

 

Model Evaporation Rates 

• Updated coefficients based on USBR study 

• Impacts surface heating and mixing 

• Represents seasonal trends well 

• Overshoots in summer 

(Padre Bay) 

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 Not for Citation or Distribution." 
 

 

New Weather Stations 

• Better understand over-water conditions 

• Fill in spatial gaps in data 

• Installed in May 2023 

Oak Creek Bay 

Bullfrog, UT 

Padre 

Bay 

Page, AZ 

Escalante 

Confluence 

Escalante 

Oak Creek 
 

Understanding Wind Speed 

 Over-land vs over-water 

• Different within-day 

patterns 

• Different magnitudes 

 Model currently uses overland weather inputs 

 Need to correct for timing and 

magnitude 

 Important b/c controls: 

• Surface evaporation rates 

• Convective mixing 

• Internal seiche 

Over-water measurements (Padre Bay) 

Over-land measurements (Bullfrog) 

Hour of Day 

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 Not for Citation or Distribution." 
 

 

Ongoing model development: River Inputs 

 Modeled Colorado River inputs 

 1D wave routing 

 Discharge, Temperature, TDS 

 Colorado River @ Cisco UT 

+ Green River @ Green River UT 

+ San Rafael River 

 ~225 km of river 

 No data gaps in model inputs 

 Higher temporal resolution 

 Within day variability 

Modeled Colorado River Inflow TDS 

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 Not for Citation or Distribution." 
 

Sensitivity Analysis (2022) 

(Test case warmer) 

(Test case Cooler) 

Test Cases: 

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

Sensitivity Analysis (2022) 

(Test case warmer) Tin dominates in summer 

(Test case Cooler) 

SRO dominates 

in winter and spring 

Test Cases: 

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

Sensitivity Analysis (2023) 

Inflow temperatures important in high inflow year 

(Test case warmer) 

(Test case Cooler) 

Test Cases: 

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

 

How are model predictions looking? 

• Improvements are being seen 

• But still some work to be done 

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

Sept. 2023 

Sampling 
 

Model Profiles 

• Surface too warm – not enough wind mixing or evaporation 

• Meta/hypolimnion too cool – more internal mixing needed 

 

Penstock 

Bypass 

Sept. 2023 

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

 

 

 

2023 Applications and Presentations 

• Modeling 

• Spring HFE 

• Near-term operations sEIS 

• LTEMP sEIS 

• Evaluating “Thermal Curtain” idea 

• Community of Practice Working Group 

• Received feed back from CE-QUAL-W2 experts 

• Most frequent comments/suggestions: 

• Wind speed might be too low 

• Check evaporation rates 
Additional Modeling Options 

 SMB Temperature Model (Yackulic and Eppehimer) 

 Predicts release temperatures (RMSE = 1.28 °C @ Lees Ferry) 

 Based on statistical regressions (inflow volume, elevation, time of year) 

 Pros 

 Very fast to run 

 Has been making good predictions 

 Cons 

 Does not model constituents (like total dissolved solids) 

 Will need updates to capture future mixing dynamics 

• Work to compare SMB to CE-QUAL-W2 

• If they both agree – more confidence in forecasting 

• If not – learning opportunity to improve one/both 
 

Next Steps 

• Continued model calibration 

• Include more constituents 

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

• Develop best forecasting practices 

• Transfer updated version to USBR 

• Predictions under mgmt. alternatives (sEIS) 
 

 

 

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