U.S. Department of the Interior 

U.S. Geological Survey 

April 2023 High-Flow Experiment 

Update on Impacts to Sediment and Sandbars 

Glen Canyon Dam Adaptive Management Program 

Adaptive Management Work Group Meeting 

November 7, 2023 

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. 
Acknowledgements 

Website: 

Bob Tusso 

https://www.usgs.gov/apps/sandbar/ 

Or 

www.gcmrc.gov/sandbar/ 

Suspended Sediment: 

David Topping and Project A staff 

Remote Camera Downloads: 

Bob Tusso and Katie Chapman 

Columbine Reach Surveys: 

Paul Grams, Katie Chapman, Matt 

Kaplinski, Erica Byerley, Gerard Salter, 

Shannon Sartain, Karen Koestner, and 

Keith Kohl 
 

 

April 2023 HFE – Planned and observed discharge 

Plan: 

72 hr at 39,500 cfs 

https://www.usbr.gov/uc/progact/amp/ltemp.html 

Observed discharge at 

Lees Ferry: 

66 hr at 39,000 to 

40,000 cfs (79-hr 

above ~30k cfs) 

• ~40,000 cfs at Lees Ferry, RM 30, and RM 61 

• ~42,000 cfs at RM 87 

• ~45,000 cfs at RM 165 and 225 

5,000 cfs of tributary 

inflows during HFE! 

Data from www.gcmrc.gov/discharge_qw_sediment 
 

 

 

April 2023 HFE – modeled vs. observed sediment balance 

Model-predicted 1-year 

sediment budget 

(7/1/2022 to 7/1/2023) 

• HFE for 72-hours at ~40,000 cfs was designed based on sand that 

accumulated in Marble Canyon from July 1, 2022 through October 2022 

and remained in Marble Canyon during the low winter 2022/2023 releases. 

Preliminary results, subject to review and revision, please do not cite 
 

 

Model-predicted 1-year 

sediment budget 

(7/1/2022 to 7/1/2023) 

 

April 2023 HFE – modeled vs. observed sediment balance 

Preliminary results, subject to review and revision, please do not cite 

Measured 1-year 

sediment budget 

(7/1/2022 to 7/1/2023) 

Modeled and measured budgets 

agree within uncertainty 
 

 

 

 

 

 

 

Summer reservoir balancing releases exported more sand 

from Marble Canyon than April HFE 

Preliminary results, subject to review and revision, please do not cite 

The sand exported by HFEs is the “cost” 

for accomplishing the goal of building 

sandbars at high-elevations 

HFE export: 

~830,000 metric tons 

May-Aug export: 

~1,126,000 metric tons 

The sand exported during May-Aug releases includes 

erosion of some of the HFE deposits and some 

redeposition at lower elevations 
 

 

Reservoir equalization/balancing releases export 3 to 5 

times more sand than average summer releases 

May-Aug sand load in 2011 was 

~2.3 million metric tons 

May-Aug sand load in 2023 was 

~1.5 million metric tons 

Average May-Aug sand load for 

2012-2022 was 428,000 metric tons 

Data from www.gcmrc.gov/discharge_qw_sediment 
 

 

Preliminary Remote Camera Results from April HFE 

• At least some deposition at 

more than 85% of 

monitoring sites with 

remote cameras 

• At some sites, deposition 

was offset by erosion 

• Vegetation scour or burial 

at many sites 

• Gullies eroded by 

monsoon storms filled 

• Similar number of gainers 

compared to previous 

HFEs. 

– Different water levels make 

comparison with previous 

HFEs difficult 

Deposition at sites throughout 

Marble and Grand Canyons 

Preliminary results, subject to review and revision, please do not cite 
 

 

 

 

Preliminary Remote Camera Results from April HFE 

Number of sand “gainers” for each HFE 

• At least some deposition at 

more than 85% of 

monitoring sites with 

remote cameras 

• At some sites, deposition 

was offset by erosion 

• Vegetation scour or burial 

at many sites 

• Gullies eroded by 

monsoon storms filled 

• Similar number of gainers 

compared to previous 

HFEs. 

– Different water levels make 

comparison with previous 

HFEs difficult 

Preliminary results, subject to review and revision, please do not cite 
 

Lone Cedar Camp – River Mile 24.5, Left 

Preliminary results, subject to review and revision, please do not cite 

April 23, 2023 
 

Lone Cedar Camp – River Mile 24.5, Left 

Preliminary results, subject to review and revision, please do not cite 

April 28, 2023 

HFE resulted in highelevation deposition 

and filled gullies 
 

Lone Cedar Camp – River Mile 24.5, Left 

Preliminary results, subject to review and revision, please do not cite 

October 3, 2023 
 

Lone Cedar Camp – River Mile 24.5, Left 

High-elevation HFE 

deposits remain. 

Mid-elevation HFE 

deposits eroded. 

Preliminary results, subject to review and revision, please do not cite 

October 3, 2023 
 

Big Dune Camp – River Mile 119, Left 

Preliminary results, subject to review and revision, please do not cite 

April 24, 2023 
 

Big Dune Camp – River Mile 119, Left 

Preliminary results, subject to review and revision, please do not cite 

April 29, 2023 

HFE resulted in highelevation deposition 

and scoured/buried 

vegetation 
 

Big Dune Camp – River Mile 119, Left 

Preliminary results, subject to review and revision, please do not cite 

October 13, 2023 
 

Big Dune Camp – River Mile 119, Left 

Preliminary results, subject to review and revision, please do not cite 

October 13, 2023 

High-elevation HFE 

deposits eroded. 

Replaced by lowelevation deposit 
 

Pumpkin Springs Camp – River Mile 213, Left 

Preliminary results, subject to review and revision, please do not cite 

April 25, 2023 
 

Pumpkin Springs Camp – River Mile 213, Left 

Preliminary results, subject to review and revision, please do not cite 

April 30, 2023 

HFE resulted in highelevation deposition 

and scoured/buried 

vegetation 
 

Pumpkin Springs Camp – River Mile 213, Left 

Preliminary results, subject to review and revision, please do not cite 

October 18, 2023 

High-elevation HFE 

deposits eroded. 
 

 

 

 

 

Summary 

• Substantial deposition at most sites from Upper Marble Canyon to

Diamond Creek

• Magnitude of sandbar building was comparable to previous HFEs

• Reservoir balancing flows in May-August exported ~1.5 million tons

(+/-20%) of sand past Diamond Creek, 3 times more than average for

that period

• High dam releases caused substantial erosion, but HFE deposits do

remain

• Low releases in September and October exposed low-elevation sand

deposits

• We will report on results from October sandbar survey at Annual

Reporting Meeting

Preliminary results, subject to review and revision, please do not cite 

Website: 

https://www.usgs.gov/apps/sandbar/