Sandbars and Sediment Storage in Marble 

and Grand Canyons: Response to Recent 

High-flow Experiments and Long-term 

Trends

GCMRC Project A (now Project 3)

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

Hadley2, 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 HFEs implemented under HFE 

protocol

• Changes in sandbars over different time scales

– Since start of HFE protocol

– Since 2002

– Since 1990

– Since 1984

– Pre-dam, pre-ROD, and Now

• Sand budget

– Effect of equalization flows

– Effect of HFEs since 2012

• Modeling, Methods for bed texture classification, Sandbar 

geochemistry, interactions between bed sediment and 

suspended sediment (won’t get to these)
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
RM 22 R – Returned to pre-HFE size by February (about same response as 2012)

11/18/2013

11/11/2013 0

1

02/12/2014 0

05/02/2014 0

more photos at poster session
11/18 11/11 05/02 02/12/2013 /2014 /2014

Photos at www.gcmrc.gov/sandbar/

RM 22: 2013 HFE – pre-flood
11/18 05/02 02/12/2013 /2014 /2014

Photos at www.gcmrc.gov/sandbar/

RM 22: 2013 HFE – post-flood
05/02 02/12/2014 /2014

Photos at www.gcmrc.gov/sandbar/

RM 22: 2013 HFE – 3 months post-flood
2014 HFE

• 22 sites (58%) 

larger

• 11 sites (29%) 

no change

• 5 sites (13%) 

smaller

November 8, 2014

November 17, 2014

more photos at poster session Photos at www.gcmrc.gov/sandbar/

119 R

Tusso et al. (preliminary data, do not cite)
Response to HFE Protocol

• Each of the HFEs in 

the past 3 years has 

resulted in sandbar 

deposition

– They continue to 

erode in following 6 

to 12 months

Photos at www.gcmrc.gov/sandbar/

2012 HFE 2013 HFE 2014 HFE

Tusso et al. (preliminary data, do not cite)
Sandbars: 2002-present

• Increase in volume in both Marble Canyon and Grand Canyon at long-term 

monitoring sites

– Deposition by HFEs

– Bars erode following HFEs, but not quite to pre-flood size

• Frequent HFEs = consistently larger bars

• Cumulative effect? No evidence yet that bars will get progressively larger.

• 2013 and 2014 HFEs were smaller than 2012 and earlier.

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2004 HFE 2008 HFE

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2014

HFEs

2002 2006 2008 2012

Marble Canyon, n=23

Grand Canyon, n=22

2014

2004 HFE 2008 HFE

2012-2014 HFEs

Hazel et al. (preliminary data, do not cite)

~10 months after 

HFEs, bars still larger 

than before start of 

protocol
Sandbars: 2002-present

• Maps of sand area from 

remote sensing images 

(2002,2005, and 2009) also 

show larger sand area in 

2009 than 2002

– Increase in wide reaches

– No change in narrow 

reaches

Sankey et al. (preliminary data, do not cite)
Sandbars: 2002-present

• Maps of sand area from 

remote sensing images 

(2002,2005, and 2009) also 

show larger sand area in 

2009 than 2002

– Increase in wide reaches

– No change in narrow reaches

• But...

• All images taken at different 

intervals following HFEs

– Bar area is predictable based 

on elapsed time since most 

recent controlled flood

– HFEs have had similar effects 

and similar erosion rates since 

1996

Ross and Grams (2015)
Sandbars: 1990-present

• 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

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2004 HFE2008 HFE

2014 HFEs

2012-2014 HFEs

1996 HFE

2000 powerplant release

Hazel et al. (preliminary data, do not cite)

Grand Canyon: bars 

about as large as 

ever measured

Marble Canyon: bars 

larger than low 

point; smaller than 

early 1990’s
Sandbars: 1984-present

• High-resolution photogrammetry 

applied to aerial photographs from 

October 1984 to map sandbar 

topography

• Allows measurement of bar volume for 

comparison with recent 

measurements

• Although some bars were much larger 

in 1984, they were not all larger

– Some are larger now

– Some about the same

• Which sites require large floods (larger 

than HFEs) to build large sandbars?

Hazel, Gushue, and Weber 

(preliminary data, do not cite)
Sandbars: pre-dam, pre-ROD, and present

YEAR PERIOD

1935 Pre-dam

1965 Post-dam; 

unrestricted

powerplant

operations 

(pre-ROD)

1973

1984

1990

March

1996

Post-dam: 

restricted 

powerplant

operations

and 

controlled 

floods

April 1996

2002

2005

2009

• Maps of sand area from air photos for 

study reaches mapped by Schmidt and 

students at Utah State

• 5 reaches between RM 0 and RM 73

• In most reaches, bars larger in 1935 than 

in post-dam years

Ross and Grams (2015)
• Bars smaller in post-dam 

periods than pre-dam 

period

• Bars larger in period of 

HFEs and restricted 

powerplant operations 

(MLFF) than period 

without HFEs and with 

unrestricted powerplant

operations (pre-ROD)

Pre-dam

Unrestricted powerplant operations; no controlled floods (pre-ROD)

Restricted powerplant operations and controlled floods (MLFF + HFEs)

Ross and Grams (2015)

Sandbars: pre-dam, pre-ROD, and present
Sand Storage in Lower Marble Canyon: 2009-2012

• Repeat maps of river bed used to track changes in sand storage and 

changes in bed texture

• Show where changes in storage occur

Grams et al. (preliminary data, do not cite)
• Sand loss during 

equalization flows

– Over short (3-year) period 

have similar uncertainty to 

flux measurements)

– Over long (10-20 year) 

period have much less 

uncertainty than flux 

measurements

• Most erosion from 

channel

– No net loss from eddies

– But there was erosion of 

high-elevation (above 

8,000 cfs stage) bars

Grams et al. (2015)

Sand Storage in Lower Marble Canyon: 2009-2012
• Sand loss not uniform 

throughout Lower Marble 

Canyon

• Adjacent reaches can have very 

different response

• But we can now begin to define 

scales over which response is 

consistent

• Seem to be ~10 reaches of 

consistent response

• We can also begin to identify 

scales where eddy response and 

bar response are linked

– Not at reaches less than ~5km

– Yes at reaches of ~ 7-12 km

– Less at longer reaches

Grams et al. (2015)

Sand Storage in Lower Marble Canyon: 2009-2012
• 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

Hazel et al. (preliminary 2014

data, do not cite)
Summary

• HFEs continue to build sandbars

• Bars continue to erode between HFEs

• Results in larger bars than would occur in 

absence of HFEs

• No evidence for “progressive” increases in 

sandbar size throughout Marble Canyon

– May occur in Grand Canyon and at some sites in Marble 

Canyon

• Trends: 2002 to 2014

– Based on looking at lots of sandbars on air photos, bar 

area about the same, but variable depending on when 

you’re looking (how long since most recent HFE)

– Based on looking at NAU long-term monitoring sites (45 

sites in Marble and Grand Canyons), bar volume larger 

now than 2002
Summary

• Equalization flows cause sand evacuation

– The eddies appear to provide a large buffer 

during periods of evacuation

• First three years of HFE protocol has been a 

period of low annual release volumes and good 

tributary sand supply

– Bar deposition without depleting sand from 

storage

– Sand has accumulated in Marble Canyon, 

replenishing sand evacuated during 2011 

equalization