Project A: Streamflow, Water Quality, and Sediment

Transport and Budgeting in the Colorado River Ecosystem

David J. Topping, U.S. Geological Survey, SBSC, GCMRC

We collect, post, and analyze the following data at stations located through the 

Colorado River Ecosystem, including key tributaries...

• Element 1: Stream gaging

– Stage

– Discharge

• Element 2: Water quality

– Water temperature

– Salinity (specific conductance)

– Turbidity

– Dissolved Oxygen

• Element 3: Sediment transport and budgeting

– Suspended- and bed-sediment data

– Sediment loads (silt and clay loads and sand loads)

– User-interactive sand budgets in 6 reaches from Lees Ferry to Lake Mead

• All elements

– User-interactive duration-curve tool for any continuous parameter

Almost all other projects funded by the Glen Canyon Dam Adaptive Management 

Program (GCDAMP) use these data, and data from this project informs 10 LTEMP goals

Funding: GCDAMP provided $1.2 million during FY 2021
Work completed in FY 2021 addressed the following two hypotheses paraphrased 

from the Glen Canyon Dam Long-Term Experimental and Management Plan 

(LTEMP) Environmental Impact Statement (EIS) and earlier GCDAMP documents

• Glen Canyon Dam can be operated such that the sand resources in the Colorado 

River ecosystem (CRe) are sustainable.

• Glen Canyon Dam can be operated such that the other CRe resources affected by 

dam operations can be sustainably managed. In this usage, “dam operations” 

refers to the amount and quality of the water released from the dam, where 

“amount” refers to stage and streamflow, and “quality” refers to temperature, 

salinity, turbidity, and dissolved oxygen.

FY 2021 products

• All required monitoring data collected but only LARGELY processed and posted to 

Project A’s website (https://www.gcmrc.gov/discharge_qw_sediment/) and to 

NWIS

• 1 peer-reviewed article in the Journal of Geophysical Research (JGR), 2 USGS 

reports, and 2 USGS data releases published (see list in Annual Report)
Change in sand mass during 

July 1, 2021 – December 31, 2021

million metric tons

Upper Marble Canyon +1.3+0.3

Lower Marble Canyon +0.22+0.05

Eastern Grand Canyon +0.26+0.14

• Paria River supplied ~1.4 million metric tons of sand (2nd largest amount 

after summer–fall 2013 during years when HFEs were allowed)

• Little Colorado River supplied ~420,000 metric tons of sand 

• Indeterminate change of only -7,800+92,000 metric tons of sand in EastCentral Grand Canyon between 7-1-2021 and 8-30-2021

• Erosion of only 63,000+49,000 metric tons of sand from West-Central 

Grand Canyon between 7-1-2021 and 8-30-2021

Data from U.S. Geological Survey (2022)
2021 Journal of Geophysical Research article synthesizing 

1998–2017 sediment results from Project A
Major results from 2021 JGR article

• Under >8.23 million-acre-foot releases, only those High-Flow Experiments (HFEs) 

released within several months of a large Paria River flood will have access to the 

finest sand size classes that lead to the largest sandbar-deposition rates in Marble 

Canyon. 

• Multi-year sand accumulation is only possible during years when the tributary 

sand supply exceeds ~130% of average and dam-released discharges are below the 

1964–2017 average. 

• Sand erodes during years of below-average to average tributary sand supply and 

higher discharge. 

• Maintaining a sufficient sand supply (bank account) to rebuild sandbars may 

require timing periods of higher and lower dam-released discharge based on 

tributary sand-supply conditions. 

• Whether the sand resources of the Colorado River in Grand Canyon National Park 

can be sustainably managed in perpetuity therefore remains an open question.

Topping and others (JGR, 2021)
Two conditions must be met to enlarge 

high-elevation sandbars

1) High stage

2) Large amount of 

relatively fine 

sand on the bed

Post-HFE volume only 10% of 

pre-HFE volume when bed-sand 

was coarse during 1996 HFE!

Figures from Topping and others (2019)

Sandbar n = 2

(RM 63.5, 65.1)
Some of the sand involved in sandbar deposition 

during HFEs is part of a “bank account” that cannot 

be replaced

• Although the Paria River is 

by far the dominant 

modern supplier of sand 

(Topping and others, JGR, 

2021), a large percentage 

(~30–50%) of the sand 

stored in sandbars is relict 

“pre-dam” sand (Chapman 

and others, GSA Bulletin, 

2020)

• Stratigraphic and groundpenetrating-radar data 

suggest strongly that predam sand exists at depth in 

at least some sandbars 

(Barnhardt and others, 

USGS-OFR, 2001)
Downward spiral has likely occurred in long-term sand mass balance...

and reflected in the high-elevation volume of an unknown percentage 

of the sandbars

>28 million metric tons of sand eroded since 1963, mostly during 3–4 

periods of sustained high dam releases (Topping and others, JGR, 2021)

Figures from Topping and others (JGR, 2021) Preliminary figures from Grams, Gushue, Hazel (do not cite)

*~5.5 million Mg 

sand erosion 

measured but 

not predicted in 

1965

*>2 million Mg 

sand erosion 

measured but 

not predicted in 

1965

*

*
Sustainable management of sand under the LTEMP sediment goal 

thus requires neutral to positive trends in both the sand mass 

balance (i.e., the bank account) and the high-elevation sandbar 

volume (i.e., your expenditures) over decades

Not sustainable Not ultimately sustainable 

because sandbar response 

lags mass balance

“Living on credit”

Sustainable

“Living 

within your 

means”

Paria

HFE

Paria

HFE
Metrics Example: The Bank Account

POSSIBLE SUCCESS! Sustainable in 

Lower Marble Canyon if highelevation sandbar volume is positive 

during this period.

POSSIBLE FAILURE Not sustainable in 

Eastern Grand Canyon regardless of 

whether high-elevation sandbar 

volume is positive during this period.

Sand bank account is being depleted. 

Will this situation turn around should 

larger Little Colorado River floods 

occur? 

Data from Topping and others, JGR, 2021; USGS (2022)
Thank you
References

• Barnhardt, W.A., Kayen, R., Rubin, D., and Minasian, D.L., 2001, The internal structure of sand bars on the Colorado 

River, Grand Canyon, as determined by ground-penetrating radar: U.S. Geological Survey Open-File Report 2001-

425, 74 p. https://doi.org/10.3133/ofr01425

• Chapman, K.A., Best, R.J., Smith, M.E., Mueller, E.R., Grams, P.E., and Parnell, R.A., 2020, Estimating the 

contribution of tributary sand inputs to controlled flood deposits for sandbar restoration using elemental tracers, 

Colorado River, Grand Canyon National Park, Arizona: Geological Society of America Bulletin, v. 133, p. 1141–1156. 

https://doi.org/10.1130/B35642.1

• Topping, D.J., Grams, P.E., Griffiths, R.E., Hazel, J.E., Jr., Kaplinski, M., Dean, D.J., Voichick, N., Unema, J.A., and 

Sabol, T.A., 2019, Optimal timing of high-flow experiments for sandbar deposition. U.S. Bureau of Reclamation, 

Glen Canyon Dam Adaptive Management Program, High-Flow Experiments Assessment Extended Abstracts, March 

2019 Annual Reporting Meeting, March 6-7, 2019, Tempe, Arizona (pp. 3–9). 

https://pubs.er.usgs.gov/publication/70203738 or https://www.usbr.gov/uc/progact/amp/amwg/2019-03-06-

amwg-meeting/20190301-HFE_Extended_Abstracts-Combined_FINAL.pdf

• Topping, D.J., Grams, P.E., Griffiths, R.E., Dean, D.J., Wright, S.A., and Unema, J.A., 2021, Self-limitation of sand 

storage in a bedrock-canyon river arising from the interaction of flow and grain size: Journal of Geophysical 

Research: Earth Surface, v. 126, e2020JF005565. https://doi.org/10.1029/2020JF005565

• U.S. Geological Survey, 2022, Discharge, sediment, and water quality monitoring, Grand Canyon Monitoring and 

Research Center: accessed on January 12, 2022, at http://www.gcmrc.gov/discharge_qw_sediment/