U.S. Department of the Interior 

U.S. Geological Survey 

April 2023 High-Flow Experiment 

Preliminary Sandbar Results 

Glen Canyon Dam Adaptive Management Program 

Technical Workgroup Meeting 

June 14, 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 

Columbine Reach Surveys: 

Paul Grams, Katie Chapman, Matt 

Kaplinski, Erica Byerley, Gerard Salter, 

Shannon Sartain, Karen Koestner, and 

Keith Kohl 

Remote Camera Downloads: 

Bob Tusso and Katie Chapman 

Website: 

Bob Tusso 

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

Or 

www.gcmrc.gov/sandbar/ 

Suspended Sediment: 

David Topping and Project A staff 
 

Columbine Study Reach in Western Grand Canyon 

View of study reach from outside of bend at RM 273.6R 

Repeat surveys to study bed elevation 

change and bank erosion 

• Three surveys collected before, 

during and after HFE 

• One additional survey planned for 

late summer or early fall 

April 25 May 12 

April 27 

Discharge for Colorado River upstream from Diamond Creek 
 

 

 

 

 

Project A Preliminary HFE Results 

• Sand concentrations were twice as high in mid Marble Canyon during the April 2023 

HFE than during any of the 2004–2018 HFEs, but sand grain size was slightly coarser 

than during most of these earlier HFEs 

• This result is consistent with Topping and others (JGR, 2021); there was substantial 

sand accumulation in upper Marble Canyon before this HFE but a generally longer 

interval between the Paria River sand inputs and the HFE 

• Lack of laboratory staff continues to prevent timely reporting of results; stay tuned 

for comprehensive sediment-transport and sand-budgeting results posted to Project 

A’s website at (https://www.gcmrc.gov/discharge_qw_sediment/) before the August 

AMWG Meeting 

Preliminary results, subject to review and revision, please do not cite 
Sandbar monitoring for April 2023 HFE 

• Daily photos by 

remote cameras (45 

sites) 

https://www.usgs.gov

/apps/sandbar/ 

• Grand Canyon River 

Guides Adopt-a-Beach 

program 

• Annual topographic

surveys in October 

(45 sites) Flows 

• Pre-HFE: 10,000 to 14,000 cfs 

• Beginning May 1: ~18,000 cfs 

That difference can result in a large decrease in the size of the 

exposed sandbar (25% to 50% decrease) 

Discharge for Colorado River at Lees Ferry 
 

 

 

 

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 

• Different water levels make 

comparison with previous 

HFEs difficult 

Preliminary results, subject to review and revision, please do not cite 
Jackass Camp – River Mile 8, Left 

April 22, 2023 
Jackass Camp – River Mile 8, Left 

April 30, 2023 
Jackass Camp – River Mile 8, Left 

May 6, 2023 
Lone Cedar Camp – River Mile 24.5, Left 

April 23, 2023 
Lone Cedar Camp – River Mile 24.5, Left 

April 26, 2023 
Lone Cedar Camp – River Mile 24.5, Left 

April 28, 2023 
Lone Cedar Camp – River Mile 24.5, Left 

May 13, 2023 
Lone Cedar Camp – River Mile 24.5, Left 

April 30, 2023 

April 23, 2023 
The Sand Pile – River Mile 30, Right 

April 23, 2023 
The Sand Pile – River Mile 30, Right 

April 27, 2023 
The Sand Pile – River Mile 30, Right 

April 23, 2023 
Buck Farm – River Mile 41, Right 

April 23, 2023 
Buck Farm – River Mile 41, Right 

April 29, 2023 
Willie Taylor Camp – River Mile 45, Left 

April 29, 2023 
Willie Taylor Camp – River Mile 45, Left 

April 28, 2023 
Kwagunt Marsh –RM 55, Right 
Grapevine Camp – River Mile 81, Left 

April 24, 2023 
Grapevine Camp – River Mile 81, Left 

April 30, 2023 
Big Dune Camp – River Mile 119, Right 

April 24, 2023 
Big Dune Camp – River Mile 119, Right 

April 30, 2023 
National Canyon – RM 166, Left 
River Mile 202, Right 

April 24, 2023 
River Mile 202, Right 

April 29, 2023 
Pumpkin Spring Camp – River Mile 213, Left 

April 24, 2023 
Pumpkin Spring Camp – River Mile 213, Left 

April 30, 2023 
Pumpkin Spring Camp – River Mile 213, Left 

April 30, 2023 
 

 

 

 

 

Summary 

• In Marble Canyon, sand concentrations were high relative to previous HFEs 

though grain size was a bit coarser 

– Lots of sample processing still to be done before final results on sand concentrations 

and sand budgets for HFE 

• Substantial deposition at most sites from Upper Marble Canyon to 

Diamond Creek 

• High dam releases in May and June inundate much of the newly deposited 

sand and will likely result in accelerated rates of erosion through the 

summer 

• We will conduct a complete sandbar survey in October and measure how 

much of the HFE deposits remain 

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

Website: 

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