Sandbars and Sediment Storage in Marble 

and Grand Canyons: Response to Recent 

High-flow Experiments and Long-term 

Trends

GCMRC Project 3

Paul Grams1, Tim Andrews1, Daniel Buscombe1, Tom Gushue1, Dan 

Hamill, Joseph Hazel2, Matt Kaplinski2, Keith Kohl1, Erich Mueller1, 

Robert Ross1, Robert Tusso1

1U.S. Geological Survey, Grand Canyon Monitoring and Research Center

2Northern Arizona University
Overview

• Sandbar response to High-Flow Experiments (HFEs) 

implemented under HFE protocol

• Changes in campsite area

• Relation between dam release volumes, sand 

retention, and sandbar erosion

• Modeling (Erich Mueller talk)

• Bedload transport (Daniel Buscombe talk)
Review of Problem: Sediment budget affected by 

disruption of sand supply and change in flow regime

Grand Canyon

~ 16% of pre-dam sand supply

Little Colorado River

Marble Canyon

~ 6% of pre-dam 

sand supply

Glen Canyon Dam

Paria River
River Mile (RM) 30 R

02/05/2015

11/09/2014 11/17/2014

09/23/2015

HFE Deposition 

Summer 2015 erosion
Photos at www.gcmrc.gov/sandbar/

RM 23: 2014 HFE – pre-flood

11/09/2014
Photos at www.gcmrc.gov/sandbar/

RM 23: 2014 HFE – post-flood

11/16/2014
Photos at www.gcmrc.gov/sandbar/

RM 23: 2014 HFE – 3 months post-flood

2/05/2015
Photos at www.gcmrc.gov/sandbar/

RM 23: 2014 HFE – 6 months post-flood

5/07/2015
Photos at www.gcmrc.gov/sandbar/

RM 23: 2014 HFE – 9 months post-flood

8/05/2015
Photos at www.gcmrc.gov/sandbar/

RM 23: 2014 HFE – 11 months post-flood

9/23/2015
2014 HFE

• Immediate post-flood

– 22 sites (58%) larger

– 11 sites (29%) no change

– 5 sites (13%) smaller

November 8, 2014

November 17, 2014

Photos at www.gcmrc.gov/sandbar/ September 5, 2015 119 R

119 R

119 R

• 11 Months post-flood

– 24 sites (60%) no change

– 17 sites (40%) smaller
Response to HFE Protocol

• Each of the three 

HFEs between 2012 

and 2015 resulted in 

sandbar deposition

– Bars eroded in 6 to 

12 month period 

after each HFE

• By October 2015, 

no bars larger than 

before the 2014 

HFE

Photos at www.gcmrc.gov/sandbar/

2012 HFE 2013 HFE 2014 HFE

preliminary data, do not cite
Sandbars: 1990-2014

• 30 monitoring sites have data to 1990

– 12 in Marble Canyon

– 18 in Grand Canyon

• Increase in sandbar volume at sites in Grand Canyon

• Marble Canyon bars still less volume than 1990, but larger than low point of 2001-2003

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1990 1995 2000 2005

1996 HFE

2004 HFE

2010

Marble Canyon, n=12

Grand Canyon, n=18

2015

2008 HFE 2012

-

2004 HFE2008 HFE

2014 HFEs

2012-2014 HFEs

1996 HFE

2000 powerplant release

Grand Canyon: bars 

about as large as 

ever measured

Marble Canyon: bars 

larger than low 

point; smaller than 

early 1990’s

preliminary data, do not cite
Sandbars: 2008-present

• 50 individual sandbars with data 2008-present

– 25 in Marble Canyon

– 7 in Grand Canyon (RM 60-87)

– 18 in Grand Canyon (below RM 87)

• With October 2008 as reference (8-month post-HFE)

– Increase in Marble Canyon and Grand Canyon (below RM 87) 

– No change in Grand Canyon (RM60-87) 2008 HFE

Marble Canyon: 

slightly larger than 

Oct. 2008

Grand Canyon 

(below RM 87): large 

relative to Oct. 2008

2012 HFE2013 HFE2014 HFE

Grand Canyon 

(RM60-87): same 

relative to Oct. 2008

preliminary data, do not cite
Downstream Trends in Sandbar Response to recent HFE’s

• 2012 HFE

– Mean positive response in all reaches

• 2013 HFE

– Mean positive response in Marble Canyon only

– Mean neutral in all of Grand Canyon

• 2014 HFE

– Mean positive response in Grand Canyon (below RM 87) only

– Slight negative response in Marble Canyon

– Neutral response in Grand Canyon (RM 60-87)

Sandbar volume evaluated 11 months following each HFE

preliminary data, do not cite
Campsite Area: 1998-2014

• Slight increases in Marble 

Canyon and Grand Canyon 

since start of HFE protocol

• Most of those increases 

occurred in “critical” campsite 

segments

• Net declines in campsite area 

between 2002 and 2009 result 

approximately equally from 

vegetation encroachment and 

sandbar erosion (Hadley, 

2014)

preliminary data, do not cite
Relation between Dam Releases and retention of Paria sand 

inputs and sandbar response

Greater retention of Paria

River sand inputs

Larger average release volumes result in 

greater export of sand inputs (Jack Schmidt 

plot of data from GCMRC web site)

Larger average release volumes result 

in greater rates of sandbar erosion 

following HFE’s (Hazel et al., 2010)

preliminary data, do not cite
• Since 2012, each year has had enough 

sand accumulation to have a controlled 

flood and have sand accumulation

• Accumulation has more than replaced 

“evacuation” that occurred in 2011

2012 HFE 2013 HFE 2014 HFE

Sand Storage in Marble Canyon During HFE Protocol

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Mean Dai yl Discharge

from

Glen Canyon Dam (ft3/s)

2000 2004

2004 HFE 2008 HFE

2010

2012

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2014

HFEs

2002 2006 2008 2012

Marble Canyon, n=23

Grand Canyon, n=22

2014

preliminary data, do not cite
Summary

• HFEs continue to build sandbars

• Bars continue to erode between HFEs

– Greater erosion in years of higher release volumes

• Sandbars larger than periods with no HFEs

• Bars larger now than at start of HFE 

protocol, but no evidence for “progressive” 

increases in sandbar size 

• High-elevation Campsite area (above 25,000 

cfs stage)

– No net change in non-critical reaches

– Increase from 2012 to 2014 in critical reaches

• First three years of HFE protocol were a 

period of low annual release volumes and 

good tributary sand supply

– Bar deposition without depleting sand from 

storage

– Sand accumulated in Marble Canyon, 

replenishing sand evacuated during 2011 

equalization