U.S. Department of the Interior 

U.S. Geological Survey 

 

 

Project B Update and 

Riverbed and sandbar response to dam operations and high-flow experiments 

Glen Canyon Dam Adaptive Management Program 

Adaptive Management Working Group Meeting 

February 28, 2024 

Paul Grams 

U.S. Geological Survey 

Southwest Biological Science Center 

Grand Canyon Monitoring and Research Center 

*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. 
 

 

Sandbar response to 2023 HFE 

2023 HFE 

• Reattachment bars and upper pool bars as large or larger 

compared to 2013-2019 

• Separation and undifferentiated bars increased, but not 

as large as some previous years 

• HFE reversed 2019 to 2022 downward 

trend 

• Increases in bar volume at most, but not 

all, sites 

Hazel and others (2022); www.usgs.gov/apps/sandbar 
 

 

 

 

 

 

 

Why measure sand storage by 

mapping the riverbed? 

• Sandbar replenishment controlled by: 

– Flow (need high flows to build large bars) 

– Sand supply (if supply in the channel is low, a 

net loss from eddy sandbars is risked) 

• Sand supply is controlled by: 

– Dam releases (annual volume and release 

pattern) 

– Inputs from tributaries 

• The sand that builds sandbars is stored on the 

bed of the river and understanding the sand 

supply is critical to understanding and 

predicting sandbar response Adapted from Hazel and others (2010) 
 

 

 

 

 

Repeat channel mapping in Lower Marble Canyon 

• Repeat measurements of channel bed (red points) verify mass balance sand budget 

(black line with gray uncertainty band) 

• Sand budget has trended upward with the exception of periods of high dam release 

volumes (equalization and reservoir balancing flows) 

www.gcmrc.gov/discharge_qw_sediment; Grams et al., 2018; and Preliminary results. Do not cite. 
How are channel mapping data used to evaluate the 

effects of dam operations? 

“high-elevation sandbar” 

 

 

 

loss gain 

Mining Accumulating sand from sand and storage to building build sandbars sandbars 

Mining Accumulating 

sand and sand, but not 

losing building 

sandbars sandbars. 

loss gain 

“total sand storage in 

channel and eddies” 
 

Repeat channel mapping: Implications for 

high flows and dam management 

Repeat measurements during HFEs (diamonds) 

• HFEs are “deficit spending” 

• Need to mobilize all the sand to build sandbars and a 

large fraction is exported 

• But a short-term negative that can be recovered from 

Repeat measurements over many years (circles) 

• Downward spiral: Equalization flows and no HFEs 

• Deficit spending: Equalization flows and HFEs 

• Sustainable: No equalization flows and HFEs 

Schmidt and Grams, 2011; Grams et al. 2018; and Preliminary results. Do not cite. 

The 2004 and 2008 HFEs demonstrated sandbar building under 

conditions of greater sand enrichment was most effective with less 

erosion of sand from storage in eddies and channel (Hazel and 

others, 2010; Schmidt and Grams, 2011). 
 

Project B: Channel Response to High 

Flows in Western Grand Canyon 

• The bed in the reach is dynamic 

– 2 to 3 m of scour and fill in scour holes during 

high flows (SDF and HFE) 

– ~ 0.5 m of bed variability in dune fields across

all flows 

– Slight aggradation of dunes during high flows, 

but followed by slight erosion after high flows 

– No systematic correlation between bar heights 

and discharge. 

• Mean condition of the channel is relatively 

stable 

– Likely controlled by downstream Pearce Ferry 

Rapid 

• Banks are eroding but erosion rate does 

not appear to be accelerated by HFEs 

Preliminary results, subject to review, o not cite. 
 

Project B: Modeling 

Two-dimensional hydrodynamic model for Glen Canyon 

Modeled current velocity at 8,000 ft3/s, near mile -12. 

Wright, S.A., Kaplinski, M., and Grams, P.E., 2024, Hydrodynamic model 

of the Colorado River, Glen Canyon Dam to Lees Ferry in Glen Canyon 

National Recreation Area, Arizona: tables of model results and accuracy 

assessment: U.S. Geological Survey data release, 

https://doi.org/10.5066/P1QTRNEB. 

 

 

 

Sand mass balance and sandbar modeling for 

Reclamation compliance (IG SEIS and LTEMP SEIS) 

4000 

3) Mean Sandbar volume (m 3500 

3000 

2500 

2000 

No Action 

One-Year Window, No Flow Spikes 

Flow Spikes RM15 

Flow Spikes LCR 

Non-bypass Alternative 

Jan 2024 Jul 2024 Jan 2025 Jul 2025 Jan 2026 Jul 2026 Jan 2027 Jul 2027 

time 

Marble Canyon Sand Mass Balance (Tmt) 2000 

1500 

1000 

500 

0 

-500 

-1000 

Jan 2024 Jul 2024 Jan 2025 Jul 2025 Jan 2026 Jul 2026 Jan 2027 Jul 2027 

time 

3580 

Lake Powell elevation (ft) 3560 

3540 

3520 

3500 

3480 

No HFEs 

No Action 

One-Year Window, No Flow Spikes 

Flow Spikes RM15 

Flow Spikes LCR 

Non-bypass Alternative 

3500 ft 

Jan 2024 Jul 2024 Jan 2025 Jul 2025 Jan 2026 Jul 2026 Jan 2027 Jul 2027 

time 

Salter and Grams, in review, do not cite. 
Project B References 

• Grams, P. E., Topping, D. J., Schmidt, J. C., Hazel, J. E., & Kaplinski, M. (2013). Linking morphodynamic response with sediment mass balance on the 

Colorado River in Marble Canyon: Issues of scale, geomorphic setting, and sampling design. Journal of Geophysical Research, 118, 21. 

https://doi.org/doi:10.1002/jgrf.20050 

• Grams, P. E., Buscombe, D., Topping, D. J., Kaplinski, M., & Hazel, J. E. (2018). How many measurements are required to construct an accurate sand budget 

in a large river? Insights from analyses of signal and noise. Earth Surface Processes and Landforms, 44(1), 160 –178. https://doi.org/10.1002/esp.4489 

• Hazel Jr., J. E., Grams, P. E., Schmidt, J. C., & Kaplinski, M. (2010). Sandbar response following the 2008 high -flow experiment on the Colorado River in 

Marble and Grand Canyons. U.S. Geological Survey Scientific Investigations Report 2010 -5015, 52 p. http://pubs.usgs.gov/sir/2010/5015 

• Hazel, J.E., Jr., Kaplinski, M.A., Hamill, D., Buscombe, D., Mueller, E.R., Ross, R.P., Kohl, K., and Grams, P.E., 2022, Multi -decadal sandbar response to flow 

management downstream from a large dam —The Glen Canyon Dam on the Colorado River in Marble and Grand Canyons, Arizona: U.S. Geological 

Survey Professional Paper 1873, https://doi.org/10.3133/pp1873 

• Mueller, E.R., and Grams, P.E., 2021, A morphodynamic model to evaluate long -term sandbar rebuilding using controlled floods in the Grand Canyon: 

Geophysical Research Letters, v. 48, no. 9, e2021GL093007, https://doi.org/10.1029/2021GL093007. 

• Schmidt, J. C., & Grams, P. E. (2011). The high flows --physical science results. In T. S. Melis (Ed.), Effects of three high -flow experiments on the Colorado 

River ecosystem downstream from Glen Canyon Dam, Arizona, U.S. Geological Survey Circular 1366 (pp. 53 –91). https://pubs.usgs.gov/circ/1366/ 

• Topping, D. J., Rubin, D. M., & Vierra, L. E. (2000). Colorado River sediment transport 1. Natural sediment supply limitation and the influence of Glen 

Canyon Dam. Water Resources Research, 36(2), 515 –542. https://doi.org/10.1029/1999WR900285 

• Wiele, S.M., Andrews, E.D., and Griffin, E.R., 1999, The effect of sand concentration on depositional rate, magnitude, and location in the Colorado River 

below the Little Colorado River, in Webb, R.H., Schmidt, J.C., Marzolf, G.R., and Valdez, R.A., eds., The controlled flood in Grand Canyon: Washington, D.C., 

American Geophysical Union, Geophysical Monograph Series, v. 110, p. 131 –145. 

• Wright, S.A., Topping, D.J., Rubin, D.M., and Melis, T.S., 2010, An approach for modeling sediment budgets in supply -limited rivers: Water Resources 

Research, v. 46, p. 1 –18, doi:10.1029/2009WR008600. 

• U.S. Department of the Interior, 1996, Record of Decision, Operation of Glen Canyon Dam Final Environmental Impact Statement. 

• U.S. Department of the Interior, 2016, Record of Decision for the Glen Canyon Dam Long -Term Experimental and Management Plan Final Environmental 

Impact Statement, https://ltempeis.anl.gov/