U.S. Department of the Interior

U.S. Geological Survey

The Effects of High-flow Experiments and Dam Releases 

on Sandbar Erosion and Deposition in Marble and Grand 

Canyons

GCDAMP Annual Reporting Meeting

January 12, 2022

Paul Grams

U.S. Geological Survey

Southwest Biological Science Center

Grand Canyon Monitoring and Research Center

photo: Jeff Behan
Acknowledgements

Project B personnel:

Matt Kaplinski, Joseph Hazel, Katie Chapman, Robert 

Tusso, Keith Kohl, Thomas Gushue, James Hensleigh, 

Shanon Sartain, and Caitlin Andrews

Collaborators and field assistants:

GCRG, Jeff Behan, David Topping, 

Erich Mueller, Sinjin Eberle, Jesse 

Collier, Daniel Buscombe, Robert Ross, 

Daniel Hamill, David Rubin, Joel 

Sankey, Jack Schmidt, Scott Wright, 

Rod Parnell, Bryan Cooperrider, Karen 

Koestner, Emily Thompson, Daniel 

Hadley, Ryan Semptua, Geoff Gourley. 

Somer Morris. Lydia Manone, Lauren 

Tango, John O’Brien Morgan Barnard, 

Pete Koestner, Logistics team: AnnMarie, Seth Felder, Dave Foster, Clay 

Nelson, Lucien Bucci, and Fritz!

photo: Jeff Behan

photo: Geoff Gourley

photo: Geoff Gourley
Moving on...

Joe Hazel retired in June 2021 after 30+ years at 

Northern Arizona University and as a cooperator with 

Reclamation and USGS on sandbar and sedimentrelated projects in Grand Canyon

photo: Geoff Gourley

photo: Geoff Gourley

joseph.hazel@nau.edu
Project B: Sandbar and Sediment Storage Monitoring and 

Research 

• Project Elements

• B.1 Sandbar Monitoring

• B.2 Bathymetric and topographic mapping for monitoring long-term trends in 

sediment storage

• B.3 Control Network and Survey Support

• FY 2021 involvement in other projects: 

• O.2 (sediment dynamics in Western Grand Canyon) 

• L (overflight remote sensing)

• Project Objectives

• track the effects of individual High Flow Experiments (HFEs) on sandbars

• monitor the cumulative effect of successive HFEs and intervening operations on 

sandbars and sand conservation

• investigate the interactions between dam operations, sand transport, and eddy 

sandbar dynamics

• GCDAMP FY2021 Funding: $865,635

• Cooperators: Northern Arizona University, Grand Canyon River Guides, 

Southern Utah University
Project B: Publications (2021)

• Alvarez, L.V., and Grams, P.E., 2021, An eddy-resolving numerical 

model to study turbulent flow, sediment, and bed evolution using 

detached eddy simulation in a lateral separation zone at the fieldscale: Journal of Geophysical Research: Earth Surface, v. 126, no. 

10, e2021JF006149, https://doi.org/10.1029/2021JF006149.

• Durning, L.E., Sankey, J.B., Yackulic, C.B., Grams, P.E., Butterfield, 

B.J. and Sankey, T.T, 2021, Hydrologic and geomorphic effects on 

riparian plant species occurrence and encroachment—Remote 

sensing of 360 km of the Colorado River in Grand Canyon: 

Ecohydrology, e2344, https://doi.org/10.1002/eco.2344.

• 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.

• Sabol, T.A., Griffiths, R.E., Topping, D.J., Mueller, E.R., Tusso, R.B., 

and Hazel, J.E., Jr., 2021, Strandlines from large floods on the 

Colorado River in Grand Canyon National Park, Arizona: U.S. 

Geological Survey Scientific Investigations Report 2021-5048, 41 

p., https://doi.org/10.3133/sir20215048.

• Unema, J.A., Topping, D.J., Kohl, K.A., Pillow, M.J., and Caster, 

J.J., 2021, Historical floods and geomorphic change in the lower 

Little Colorado River during the late 19th to early 21st centuries: 

U.S. Geological Survey Scientific Investigations Report 2021–5049, 

34 p., https://doi.org/10.3133/sir20215049

Data and web applications

• Grams, P.E., Alvarez, L., Kaplinski, M., and Wright, S., 

2021, Repeat measurements of bathymetry, streamflow 

velocity and sediment concentration made during a high 

flow experiment on the Colorado River in Grand Canyon, 

March 2008: U.S. Geological Survey data release, 

https://doi.org/10.5066/P9O00Z44

• Grams, P.E., Hazel, J.E., Jr., Kaplinski, M., Ross, R.P., 

Hamill, D., Hensleigh, J., and Gushue, T., 2020, Longterm sandbar monitoring data along the Colorado River 

in Marble and Grand Canyons, Arizona: U.S. Geological 

Survey data release, https://doi.org/10.5066/P93F8JJK

• Sabol, T.A., Griffiths, R.E., Topping, D.J., Mueller, E.R., 

Tusso, R.B., and Hazel, Jr., J.E., 2021, Surveyed peakstage elevations, coordinates, and indicator data of 

strandlines from large floods on the Colorado River in 

Grand Canyon National Park, Arizona: U.S. Geological 

Survey data release, https://doi.org/10.5066/P9GIQ9ZN

• Images from remote camera monitoring of sandbars: 

https://grandcanyon.usgs.gov/gisapps/sandbarphotoview

er/RemoteCameraTimeSeries.html

• Images from GCRG adopt-a-beach program: 

https://grandcanyon.usgs.gov/gisapps/adopt-abeach/index.html

• Data from long-term sandbar monitoring sites: 

https://www.usgs.gov/apps/sandbar/
Project B: Key findings with respect to LTEMP Goals and 

Knowledge Assessment

• LTEMP goal: 

– “Increase and retain fine sediment volume, area, and distribution in the 

Glen, Marble, and Grand Canyon reaches above the elevation of the 

average base flow for ecological, cultural, and recreational purposes.”

• Assessment: 

– Although specific targets for sanbars are not defined, each HFE has resulted 

in deposition demonstrating that the general objective of retaining and/or 

increasing sand volume above the 8000 cfs stage can be achieved when 

sand inputs occur and HFEs are implemented (2012-2020).

• Prognosis: 

– Deposition at sandbars is likely stage-limited (bars not likely to get larger 

without larger HFEs)

– Sandbar volume increased and maintained from 2011 to 2018 when dam 

releases were relatively low and sand inputs from Paria River average or 

above and HFEs were implemented. 

– Since 2019, sandbar volume has decreased for most bar types because 

monsoon failure (2019, 2020) and low reservoir levels (2021) prevented 

HFE implementation for 3 consecutive years.

Status: moderate concern because 

sandbars are decreasing, but still larger 

than before start of HFE protocol and 

sediment supply is good

Trend: decreasing because bars have 

eroded since last HFE in 2018

Confidence: high, because the monitoring is 

robust.
Project B: AMP goals addressed and information provided

• LTEMP goal: 

– “Increase and retain fine sediment volume, area, and distribution in the Glen, Marble, and Grand 

Canyon reaches above the elevation of the average base flow for ecological, cultural, and 

recreational purposes.”

• Question from HFE Protocol: 

– “Can sandbar building during HFEs exceed sandbar erosion during periods between HFEs, such 

that sandbar size can be increased and maintained over several years?”

• Project B address these questions by two related monitoring efforts:

– Annual sandbar and campsite monitoring (sandbar surveys and daily photographs)

• Annual assessment of the effects of HFEs and other dam operations on selected sandbars and campsites.

• Assessment of immediate response to HFEs by network of remote time-lapse cameras

– Periodic channel mapping (Combined topographic and bathymetric mapping)

• Evaluation of LTEMP performance by measuring long-term trends in sand area, volume, and distribution from a large 

sample of sandbars. 

• Measurement of long-term trends in sand storage on the riverbed. 
Short update on Project B.2 

(Channel Mapping for Sandbar and Sand 

Storage Change)

• Mapped Lower Marble Canyon and Eastern Grand 

Canyon (60 river miles) in 2019

• Data processing is complete but final analysis and 

reporting has been delayed by covid-related 

staffing issues in 2020 and lots of field work 

(overflight and SDF) in 2021.

• Will be reporting in future meetings this year or at 

next ARM

• These data will provide a ~10-year status update 

on performance of HFE protocol by:

– Evaluating the effects of HFEs on more than 100 sandbars 

throughout LMC and EGC (compared to the 20 measured 

annually in this reach)

– Showing where sand eroded or deposited on the riverbed 

– Verifying the sand mass balance measured in Project A

• This April we will conduct the first channel mapping 

survey of RM 87 to RM 166, resulting in a complete 

basemap for all reaches from the dam to Diamond 

Creek

Segment (river miles) Completed Maps

Glen Canyon (-15 to 0) 2014

Upper Marble Canyon (0 to 30) 2013, 2016

Lower Marble Canyon (30 to 61) 2009, 2012, 2019

Eastern Grand Canyon (61 to 87) 2011, 2014, 2019

East Central Grand Canyon (87 to 166) 2022

West Central Grand Canyon (166 to 225) 2017

Western Grand Canyon (225 to 280) *

* A 2-mile study reach has been mapped for project O.2. 

There are no current plans to map the rest of the reach.
Pre-dam flows, dam operations, high flows, and sandbars

1952 2003

HFE-related Science and Management Questions:

• With frequent HFEs, will sandbars increase in size 

and abundance?

• Will frequent HFEs cause sand supply in channel to 

decrease and exacerbate sediment deficit?

Three major periods of flows and dam operations

Pre-dam: 

• Annual floods

• Abundant sand 

supply

• Large sandbars

Post-dam I: 

• Daily small floods

• Limited sand supply

• Eroding sandbars

• Unplanned floods (spills)

Post-dam II:

• Restricted hydropower operations

• High Flow Experiments (HFEs) 

• triggered by sand supply from 

Paria River

Pre-dam Post-dam I

photo by K. Frost photo by S. Tharnstrom
Sandbar monitoring data

Data collection: old school total station 

and survey rod

Allows data collection 

down to 8,000 cfs stage 

and in dense vegetation. 

Neither of which can be 

done reliably with modern 

methods (lidar etc.)

21st century data 

processing and analysis

Data processed 

and analyzed in 

sql database

Data served in 

sandbar web 

application

Topographic 

surfaces modeled in 

survey software

www.gcmrc.gov/sandbar OR www.usgs.gov/apps/sandbar
Sandbar monitoring study sites

20 sites in Marble 

Canyon

24 sites in Grand Canyon

(Little Colorado River to Diamond Creek)

1 site in Glen 

Canyon

Monitoring Data 

• 45 sites currently monitored

• 32 monitored since 1990

• Data collected annually in October

• 42 of the sites instrumented with 

remote cameras

*Only reporting on first 28 sites (RM 0 to 93) today. 
Sandbar monitoring site types

Mueller and others (2018)

Narrow Reattachment bars

Medium Reattachment bars

Wide Reattachment bars

65R

22R

194L

Reattachment Bars

Increasing vegetation

Increasing channel width

Undifferentiated bars

Separation bars

Upper pool deposits

35L

24L

104R

Other Bar Types
Sandbar monitoring results: Sites between RM 0 and RM 93*

*2021 data processed for 28 out of 44 sites Preliminary results, subject to review, do not cite

Narrow Reattachment bars Medium Reattachment bars

Wide Reattachment bars Upper pool deposits

• Most response to HFEs.

• Moderate vegetation

expansion.

• Common campsites.

• Net decrease 2020 to 2021

Separation bars Undifferentiated

• Least responsive to HFEs.

• Heavy vegetation

expansion.

• Less common campsites.

• Net increase 2020 to 2021.

• Variable response to HFEs.

• Moderate vegetation

expansion.

• Common campsites.

• Net decrease 2020 to 2021.
Sandbar monitoring results by bar type: 1990 to 2021

All sand above 8,000 ft3/s stage (includes fluctuating 

zone intermittently available for camping)

• 2020 to 2021 decrease in all types.

• Largest decrease in Separation and Undifferentiated 

bars.

Only sand above 25,000 ft3/s stage 

(always usable for camping)

• 2020 to 2021 decrease Narrow & Medium 

Reattachment bars and in Separation and 

Undifferentiated bars.

Preliminary results, subject to review, do not cite
Sandbar monitoring results averaged among all bar types: 1990-2021

All sand above 8,000 ft3/s stage (includes fluctuating 

zone intermittently available for camping)

• Deposition from HFEs erodes within 1 to 2 years.

• Upward trend during HFE protocol.

• Downward trend since 2019 (last HFE).

Only sand above 25,000 ft3/s stage 

(always usable for camping)

Preliminary results, subject to review, do not cite

• Deposition from HFEs more persistent.

• Upward trend during HFE protocol.

• Smaller downward trend since 2020.
Preliminary results, subject to review, do not cite

Sandbar changes: Marble Canyon vs. Grand Canyon

1990 to 2020

• Trends in Marble Canyon and Grand Canyon are similar 

for each bar type

• Differences between bar types greater than differences 

between Marble Canyon and Grand Canyon

2020 to 2021

• Deposition in Upper Marble Canyon (RM 0 to RM 30)

• Mostly erosion downstream from RM 30
Sandbar response to HFE magnitude

Hypothesis: higher HFEs inundate the bars at 

greater depth and result in larger deposits

Data: Compared HFEs (1996, 2004, and 2008) 

with powerplant capacity “habitat 

maintenance flows” (HMFs) conducted in 

1997 and 2000.

Prediction for 2021 Spring Disturbance Flow: 

Not much deposition (will cover in afternoon 

panel discussion)

Hazel and others (in press), subject to review, do not cite

Thickness of sandbar deposits 

positively correlated with flow 

magnitude

HFE is >40,000 cfs

HMF is ~30,000 cfs
Measurement of campsite area

• Define campsite areas by field 

survey to create polygons of 

campsites

• Campsite Area = a smooth 

substrate (sand) with no more 

than eight degrees of slope 

with little or no vegetation

• Intersect with topography to 

compute area for multiple 

elevation bins

Field survey

Campsite polygons 

intersected with topography

Campsite polygons (multiple years shown)
Campsite area in Marble and Grand Canyons

Preliminary results, subject to review, do not cite

Camp area between 15,000 and 25,000 ft3/s stage

*Only have 2021 data for sites in Marble Canyon

Camp area above 25,000 ft3/s stage

*Only have 2021 data for sites in Marble Canyon

• Low-elevation camp area most responsive to HFEs

• Decreased since last HFE in 2018

• Decrease has continued in Marble Canyon

• High-elevation camp area increased following some HFEs

• Surveys are ~11 months following HFEs, so 

• vegetation encroachment

• Decrease has continued in Marble Canyon
Vegetation expansion impact on campsites

Preli

RM 194 L

Vegetation 

expansion continues 

to occur at many 

sites

10/1/2020

11/10/2018

RM 24.5 L

4/20/1996 11/20/2016

minary results, subject to review, do not cite

Major vegetation expansion 

at wide reattachment bars in 

late 1990’s and early 2000’s 

(Hadley and others, 2018)
HFE’s and vegetation treatment

Preliminary results, subject to review, do not cite

10/15/2019

11/1/2018

1st veg removal in Summer 2019

RM 122

10/4/2021

3rd veg removal in Summer 2021

10/5/2020

11/10/2018

After HFE

2nd veg removal in Summer 2020

• NPS is conducting vegetation treatment at 3 

long-term sandbar monitoring sites

• We’ll monitor to see if treatment effects 

response to future HFEs
Summer 2021 monsoon rains impact on campsites

Tatahatso camp destroyed by hillslope runoff during monsoon rains

10/3/2020 10/2/2021
Summer 2021 monsoon rains impact on campsites

Upper Blacktail camp 

(RM 120R)

National Canyon camp 

(RM 167L)

Martha’s camp 

(RM 38.6L)

Matcat Hotel camp 

(RM 149L)

Talking Heads camp 

(RM 133.6L)

Tatahatso camp 

(RM 37.9L)
Sandbar model

Developed by former postdoc Erich Mueller. 

Models changes in sandbar volume based on:

Suspended sand flux into eddy:

qqss,iiii = λλVVeeCCss

SSdd = wwssCCee

Deposition rate in eddy:

λλVVeeCCss=λλVVeeCCoo + wwssCCeeAAee

Mass balance in eddy:

Erosion:

dd

dddd = −kk where k is rate

parameter (1/s)

Exponential decay with bar “halflife” of approximately 2 years

λ: Eddy Exchange Coefficient

Cs: Sand Concentration

D: Sand Grain Size

Sd: Sand Deposition Rate (function of settling 

velocity, ws)

e: Erosion Rate (exponential decay)

L: Bar Dimensions

A: Submerged (s) and total (tot) area

h: Thickness of submerged (s) and 

exposed (e) bar

Mueller and Grams (2021)

Mass/time

Mass/area

Total flux in = flux out + deposition
Model Results: 2002-2019

Mueller and Grams, 2021

The model predicts sandbar response for narrow reattachment bars (the “group 1a” sites of 

Mueller et al., 2018). It was calibrated using data from 9 narrow reattachment bars located 

throughout Marble and Grand Canyon. Other sandbar types tend to be less responsive.
Post-hoc Controlled Flood Scenario Modeling

Proportion of time sandbars Model simulations reducing the number of HFEs are larger during HFE protocol.

Fewer HFEs = reduced sandbar size

Without protocol, sandbars are 

that large only 20% of the 

time.

Mueller and Grams (2021)

Over the period of 

the protocol, 

sandbars are at least 

70% of maximum 

observed size for 80% 

of the time. 
Model predicts that anticipated low release volumes in 2022 lead to continued erosion

May need to re-parameterize if flows or bar conditions (i.e. vegetation) 

are considerably different than calibration period

Preliminary results based on Mueller and Grams (2021) model, subject to review, do not cite
Sandbar model for HFE scenario testing

Predict sandbar volume through summer 2022, beginning with observed size in October 2020.

Preliminary results based on Mueller and Grams (2021) model, subject to review, do not cite
Predicted sandbar volume in April 2022 relative to 

October 2021 for the four HFE scenarios

Event Expected sandbar size 

immediately after HFE

Expected sandbar size in 

April 2022

192-hr HFE + 75% + 50%

96-hr HFE + 45% + 30%

60-hr HFE + 30% + 20%

No HFE + 0% - 10%

• Although 60-hr HFE, is likely to have 

less benefit than longer duration HFEs, 

model predicts significant positive 

response

• The 65-hr HFE in 2018 resulted in bar 

deposition in all segments of Marble 

Canyon and Grand Canyon

• Most bars that increased during 

longer HFEs also increased during 

the 2018 HFE

Preliminary results based on Mueller and Grams (2021) model, subject to review, do not cite
Predicted sandbar volume in April 2022 relative to October 2021 

for a spring HFE

Preliminary results based on Mueller and Grams (2021) model, subject to review, do not cite

Event Expected sandbar 

increase from pre- to 

post-HFE

Expected sandbar size in 

April 2022 relative to 

October 2021

192-hr HFE + 75% + 50%

96-hr HFE + 45% + 30%

60-hr HFE + 30% + 20%

No HFE + 0% - 10%

96-hr Spring HFE + 38% +25%

* Modeling based on sediment inputs through midSeptember 2021 and anticipated dam releases (model 

has not been re-run with Oct.-Dec. actual releases)
Large 2021 inputs from Paria River combined with relatively low 

dam releases  Lots of sand remaining in Mable Canyon

Predicted Mable Canyon (RM 0 to 61) mass balance based 

on measured inputs through 8/31/2021

• Predicted Marble Canyon mass balance 

for Jan. 2022 was about 1.2 million Mg

• Observed as of 1/11/2021 is 1.5 ± 0.5 

million Mg

• Expect to end sediment year on 

6/30/2022 with at least ~1 million Mg 

positive sand balance in Marble Canyon

Observed Upper Mable Canyon (RM 0 to 30) 

mass balance

1.3 ± 0.4 million Mg 0.2 ± 0.1 million Mg

Preliminary results based on Wright and others (2010) model, subject to review, do not cite

Observed Lower Mable Canyon (RM 30 to 61) 

mass balance
Summary

• Channel Mapping

– Expect update in 2022

• Sandbars

– Increased during HFE protocol

– Sandbar volume has declined since most recent HFE in 2018

– Continued vegetation expansion

• Campsites

– Decreasing in area by vegetation encroachment

• Sandbar model

– Can be used to interpolate sandbar volume between annual 

surveys

– Can be used to predict response to different HFE scenarios

– Applies to “narrow reattachment bars”

• Sand supply

– Owing to large sand inputs in 2021 coupled with relatively 

low reservoir release volumes, the current sand supply in 

Marble Canyon is large

– Model predicts substantial sandbar deposition would occur 

under current sand supply conditions that are predicted to 

persist through June 2022

RM 122 (narrow reattachment bar)
References

• Hazel, J. E., Kaplinski, M., Hamill, D., Buscombe, D., Mueller, E.R., Ross, R.P., Kohl, K., and Grams, P.E., in press, 

Multi-Decadal Sandbar Response to Flow Management Downstream from a Large Dam: the Colorado River in 

Marble and Grand Canyons, Arizona. U. S. Geol. Surv. Prof. Paper xxxx.

• Mueller, E.R., Grams, P.E., Hazel, J.E., and Schmidt, J.C., 2018, Variability in eddy sandbar dynamics during two 

decades of controlled flooding of the Colorado River in the Grand Canyon: Sedimentary Geology, v. 363, p. 181–

199, doi:10.1016/j.sedgeo.2017.11.007.

• 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.

• 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.