Processing fine sediment transport data: 

procedures, processing, and bottlenecks

Ronald E. Griffiths*1

David J. Topping1

Nancy J. Hornewer2

Bradley D. Garner2

Nicholas Voichick1

Thomas A. Sabol1

David M. Sibley3

Tracey A. Reinke3

*rgriffiths@usgs.gov

1 USGS GCMRC

2 USGS AZWSC

3 USGS CIDA

2014 Annual Reporting Meeting

Phoenix, AZ

January 29, 2014
A quick downstream tour (July 1, 2013 – Jan 1, 2014)
Upper Marble Canyon

RM0 – RM30
Lower Marble Canyon

RM30 – RM61
Eastern Grand Canyon

RM61 – RM87
East Central Grand Canyon

RM87 – RM166
West Central Grand Canyon

RM166 – RM225
Western Grand Canyon

and the Lake Mead Delta

>RM225 
Overall change in sand mass in the Colorado

River between RM0 and RM225 (Lees Ferry

to Diamond Creek) during July 1, 2013 – January 1, 

2014 was:

+1.4+1.2 million metric tons (on the basis of grain size, 

likely mostly in sandbars in Marble Canyon and East 

Central Grand Canyon, RMs 0-61 and 87-166)

Overall change in sand mass in the Colorado

River below RM225 (below Diamond Creek) during July 

1, 2013 – January 1, 2014 was:

+1.4+0.1 million metric tons

(Agreement between these numbers is a coincidence)
Project B: Streamflow, Water Quality, and Sediment Transport 

 Project is more than just sediment
The following 15-minute data are current at all 

sites at: 

www.gcmrc.gov/discharge_qw_sediment/

• Gage height

• Discharge

• Water temperature

• Specific Conductance

• Dissolved Oxygen

• Turbidity

• Suspended-silt-and-clay concentration

• Suspended-sand concentration

• Suspended-sand grain size

• Silt and clay loads

• Sand loads 
The following data have been recently revised

• Paria River peak discharges 

AZ Water Science Center decreased this by 

about 25% relative to what was on the web this

fall. This resulted in a slight reduction in the reported

amount of sand supplied during 2013. 

The following data are still being processed (delivered 

by March)

• Suspended-sediment samples from Paria and 

Little Colorado Rivers

Completion of this processing will not likely result in 

much change in reported loads but will reduce 

uncertainty in 2013 sediment loads and sand 

budgets.
Steps involved in computing sediment loads and 

constructing sand budgets:

Examples from Upper Marble Canyon
Step 1: Calculate discharge at 15-minute intervals and perform QA/QC

Gage height is measured at 15-minute intervals at three stations

Stage-discharge relations are used to convert gage-height measurements 

to discharge.

Episodic discharge measurements are made to evaluate and possibly 

revise stage-discharge relations.

15-minute discharges reported in real-time on website are usually good to

within several percent, but sometimes major revisions are necessary....

All revisions of discharge during a water year (October-September) are 

finalized (by USGS standard protocols) by March of the following year.
Step 2: Measure suspended-sediment concentrations and grain-size 

distributions in major tributaries

For the Upper Marble Canyon Reach, the only major tributary is the Paria River.

Initial suspended-silt-and-clay and sand concentrations are estimated by the

physically based sediment-transport model of Topping (1997). 

Model predictions of suspended-silt-and-clay and sand concentrations are 

typically within 40% of the measured concentrations during most floods. 

Because no new technology has been found to replace physical suspendedsediment samples during the extreme sediment conditions that typify Paria

River or Little Colorado River floods, the only way to actually “know” the 

sediment concentrations during floods on these rivers is to collect MANY

physical suspended-sediment samples. 
Processing these samples through the laboratory is the ONLY MAJOR BOTTLENECK

in this project.

It takes roughly 3 person-hours to process each Paria River or Little Colorado River 

suspended-sediment sample through the laboratory.

Given the number of Paria and Little Colorado River samples needed each year, it 

would take 1 person 23 full-time weeks to process all of these samples.

We only have 2 full-time GCDAMP-funded employees in the lab...and we have 

many other samples to process for this project.
Step 3: Calculate major tributary sediment loads

Sediment loads are the product of discharge and sediment concentration, plus 

bedload.

Initial calculated sediment loads have possible persistent biases as high as ~40%.

As samples get processed through the laboratory, modeled sediment concentrations

are adjusted to agree with the measured concentrations in the samples, reducing

the maximum possible persistent biases.

Once discharges are finalized and all suspended-sediment samples have been

processed, final Paria River sediment loads are calculated.

Final Paria River sediment loads have possible persistent biases that are likely <10%.

Given the level of staffing in the laboratory and the number of samples yet to

be processed, 2013 Paria River sediment loads will not be final until March 2014.

Step 4: Measure 15-minute suspended-silt-and-clay concentrations,

suspended-sand concentrations, and suspended-sand grain size at gaging stations on the

Colorado River and perform QA/QC

Discharge-independent changes in suspended-silt-and-clay concentration and 

suspended-sand concentration exceeding several orders of magnitude occur in the 

Colorado River over timescales <1 hour

We use multi-frequency acoustics to make 15-minute measurements of suspendedsilt-and-clay concentration, suspended-sand concentration, and suspended-sand grain

size.

These acoustic measurements are verified using episodically collected physical samples 

(processed through the lab) with known error 

(Topping and others, 2011, USGS-Professional Paper 1774).

Analyses indicate that the maximum possible persistent biases in the acousticallymeasured sand concentrations are roughly 5%.
Example from Colorado River above Little Colorado River 

near Desert View, AZ, 09383100
ORANGE = EWI 

measurement 

made using a 

US D-96-A1 depthintegrating sampler

BLUE = calibrated

pump measurement

ERROR BARS = 95%

confidence-level

field + lab error
ORANGE = EWI 

measurement 

made using a 

US D-96-A1 depthintegrating sampler

BLUE = calibrated

pump measurement

ERROR BARS = 95%

confidence-level

field + lab error
Step 5: Calculate 15-minute suspended-silt-and-clay and suspended-sand loads at the 

Colorado River gaging stations using the 15-minute discharge and acoustic sedimentconcentration data

Step 6: The relatively small estimated contributions of sand to the Colorado River 

from lesser tributaries are verified every 6 months using data collected in these tributaries 

(covered in last nights poster session). Maximum possible persistent biases assigned to the 

lesser tributary sand loads in the sand budgets are 50%.
Step 7: Construct mass-balance sand budgets (SAND IN minus SAND OUT)

Tributary supply of sand to the reach is calculated by integrating the sand loads in the 

major and lesser tributaries, accumulating uncertainties set equal to the maximum possible 

persistent biases in these loads. 

The default values of these uncertainties are 10% for the finalized major tributary sand 

loads and 50% for the lesser tributary sand loads. 

Colorado River supply and export of sand from the reach is calculated by integrating 

the suspended-sand loads at the gaging stations bracketing the reach. At each of these 

gaging stations, bedload is estimated as a percentage of the suspended-sand (Rubin and 

others 2001). The measured suspended-sand load is combined with the estimated 

bedload to yield the total sand load. 

The default values of the uncertainties in the suspended-sand loads are 5%. The default

value of the bedload multiplier is 5%. 
Questions?