Comparison of sediment-transport and bar

from the 1996 and 2004 controlled-flood 

on the Colorado River in Grand C

David J. Topping (USGS)David M. Rubin (USGS)John C. Schmidt (USU)Joseph E. Hazel, Jr. (NAU)Theodore S. Melis (USGS)Scott A. Wright (USGS)Matt Kaplinski (NAU)Amy E. Draut (USGS)Michael J. Breedlove (USU)

published 2006 in Proceedings of the 8th Federal Inter-Agency Sedimentation Conference
Sandbars and other deposits 

of sand, silt, and clay are 

important because...

• Integral part of natural riverscape• Provide riparian habitat, provide 

habitat for endangered native fish, protect archeological sites, and recreation

In the upstream 40% of Grand Canyon National Park, the amount of sand in the main channel and eddies has decreased by over 25% since the 1980s, in spite of the 1996 controlled flood experiment (Rubin et al, EOS, 

2002; Flynn and Hornewer, USGSWRIR, 2003; Schmidt et al., GSA Special Paper, in revision).
• Cut off ~9

formerly sColorado boundary National WRR, 20

• Removed 

hydrograUSGS-PPboth base volumes accumulaand flood the accumchannel, into eddy 

Effects of dam operation

sediment-transport
Sand-transport paradigm prior 

1996 controlled-flood experim

• Under normal powerplant re

Canyon Dam, tributary-supaccumulate in the main chatimescales

• Accumulated sand could be 

main-channel bed to eddies floods, increasing both the tof eddy sandbars
Sand-transport paradigm prior 

1996 controlled-flood experim

• Under normal powerplant re

Canyon Dam, tributary-supaccumulate in the main chatimescales (FALSE; Rubin 

• Accumulated sand could be 

main-channel bed to eddies floods, increasing both the tof eddy sandbars (ONLY PARubin et al., EOS, 2002)
Sand-transport paradigm prior 

1996 controlled-flood experim

Reality

• During year prior to 1996 controlled flood, tributary 

sand were low and dam releases were moderate t

• 1996 controlled-flood experiment conducted durin

was relatively depleted with respect to sand

• Under normal powerplant re

Canyon Dam, tributary-supaccumulate in the main chatimescales (FALSE; Rubin 

• Accumulated sand could be 

main-channel bed to eddies floods, increasing both the tof eddy sandbars (ONLY PARubin et al., EOS, 2002)
During the 1996 controlled flood, ~3x the san

eddies above the stage associated with 8,000 

eroded from eddies below this stage (Hazel e

Mono., 1999; Schmidt, AGU Mono., 1999). ~90sediment exported was eroded from eddy san

al., JGR, 2006). 

Before and after 7-day 45,00

1996 controlled flood
Design of 2004 controlled-flood e

• Keep dam releases 

relatively low (< 10,000 ft

3/s) 

during SeptemberNovember to allow the accumulation and retention of new tributary sand inputs in the channel

• If more than 800,000 metric 

tons of new sand were retained, follow this period of lower dam releases with a 60-hour release of 41,000 ft

3/s in late November

0 1 2

.01

.1

15

102030507080909599

99.9

99.99

PARIA RIVER ANNUA

% OF YEARS IN WHICH SAND SUPPLY IS EXCEEDED

800,000 metric tons

61% OF YEA54% OF YEA55% OF YEA
30-mi

Grand Canyon g

(87-mile)

above Diamond Creek gage

(225-mile)

Glen C

LakeMead

National Canyon gage

(166-mile)

122-mile eddy 

More suspended sand in 200More suspended sand in 199

-20 to -45%
0

500

10001500

-1 0 1 2 

1996 WATER DISCHARGE2004 WATER DISCHARGE

WATER DISCHARGE (m

3

/s)

DAYS A

RIVER

0

500

10001500

0100020003000400050006000

-1 0 1 2 3 4 5 6 7 8 9

1996 WATER DISCHARGE2004 WATER DISCHARGE

1996 ESTIMATED SAND1996 ESTIMATED SILT & CLAY

2004 SILT & CLAY2004 SAND

WATER DISCHARGE (m

3

/s)

CONCENTRATION (mg/l)

DAYS AFTER ARRIVAL OF FLOOD

RIVER-MILE 30

0

500

10001500

-1 0 1 2 

1996 WATER DISCHARGE2004 WATER DISCHARGE

WATER DISCHARGE (m

3

/s)

DAYS A

RI

0

500

10001500

0100020003000400050006000

-1 0 1 2 3 4 5 6 7 8 9

1996 WATER DISCHARGE2004 WATER DISCHARGE

1996 SAND (2 VERT. P-61 SAMPLER)1996 SILT & CLAY (2 VERT. P-61 SAMPLER)1996 SAND (EDI D-77 SAMPLER)1996 SILT & CLAY (EDI D-77 SAMPLER)2004 SILT & CLAY2004 SAND

WATER DISCHARGE (m

3

/s)

CONCENTRATION (mg/l)

DAYS AFTER ARRIVAL OF FLOOD

RIVER-MILE 87

FROM 

LCR

FLOOD
0

500

10001500200025003000

0 10 20 30 40 50 60 70 

SILT & CLAY MEASURED DURING FIRST DAY OF 1996 FSAND MEASURED DURING FIRST DAY OF 1996 FLOODSILT & CLAY DURING FIRST DAY OF PEAK FLOW IN 200SAND DURING FIRST DAY OF PEAK FLOW IN 2004 FLOO

CONCENTRATION (mg/l)

RIVER MILE

PARIA RIVER

LITTLE 

COLO.

RIVER

Lagrangian sampling 
Grand Canyon g

(87-mile)

Glen C

LakeMead

National Canyon gage

(166-mile)

122-mile eddy 

1996 controlled-flood experim

Net erosionNet deposition

No net change in sand volume

downstream from 87-mile
30-mi

Grand Canyon g

(87-mile)

above Diamond Creek gage

(225-mile)

LakeMead

Net depositionNet erosion

Highest erosioupstream from 

Extremely slight net erosion between

87-mile and 225-mile

2004 controlled-flood experim

Slight 

erosio

Glen C
-300,000

-250,000-200,000-150,000-100,000

-50,000

0

50,000

0 10 20 30 40 50 60 7

CHANNELEDDIES (all elevations)EDDIES (high-elevation parts only, >

SEDIMENT MASS CHANGE (metric tons)

RIVER MILE

PARIA RIVER

LITTLE 

COLO.

RIVER

CHANGE IN SEDIMENT MASS BY ENVIRONMENT DURING 
S

to

• Abo

50% in vabo

• Bet

and sanvol8,0

• Bet

and sanvol25,

Comp1996 
30-m

Grand Canyon g

(87-mile)

P

Sediment-transport data indicate that>130,000 metric tons (>10%) of new sand in retention prior to the flood were deposited upstream from 30-mile

Multibeam-sonar, survey, airborne LiDAR data

NEGA

Net transfer of sediment into eddies during 2004 

NEGATIV

Net deposition from Lagrangian samp. trip

NEGATIV

Interpolation of multibeam data 

yields +140,000 metric tons
Conclusions

• Because subsequent dam releases do not resu

of lower-elevation parts of bars scoured during controlled floods conducted under sand-deplete(1996) cannot be used to sustain sandbar area 

• Substantial increases in total eddy-sandbar are

are only possible during controlled floods condu

sand-enriched conditions (2004) that follow larg

• In future controlled floods, more sand than was 

the 2004 controlled-flood experiment is required 

increases in total eddy-sandbar area and volumof Marble and Grand Canyons

• Tributary inputs larger than 1 million metric tons 

rare, therefore “more sand” can be achieved diraugmentation from sand trapped in the reservo

Glen Canyon Dam, or perhaps indirectly by folltributary input of sand with short-duration contro