Regulation of sand transport in the Co

by changes in the surface grain size of e

over multi-year timescales

David J. Topping (USGS)David M. Rubin (USGS)John C. Schmidt (USU)published 2005 inSedimentology, v 52

0

500

1,0001,5002,0002,5003,000

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

INSTANTANEOUS DISCHARGE (m

3

/s)

CALENDAR YEAR

1983 FLOOD

1996 CONTROLLED FLO

SUSTAINED LO

CAPACITY OF GCD POWERPLANT
Use β of Rubin and Topping (2001) in conju

observations of surface grain size to evaluaenvironment, main channel or eddy (~20% important in regulating suspended-sand tranmulti-year timescales...

β = Db Dbm

β = CCm ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ −0.1 Ds Dsm ⎛ ⎝ ⎜ ⎞ ⎠ ⎟ 0
0.4

0.50.60.70.80.91.01.11.21.31.41.51.61.71.81.92.0

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

LOWER MARBLE CGRAND CANYON G

β

CALENDAR YEAR

p < 1 x 10-16

p = 4.9 x 10-10

0.4

0.50.60.70.80.91.01.11.21.31.41.51.61.71.81.92.0

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

LOWER MARBLE CANYON GAGE

GRAND CANYON GAGE

β

FINING COARSENING

CALENDAR YEAR

< 250 m3/s DISCHARGE 

0.40.50.60.70.80.91.01.11.21.31.41.51.61.7

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

1.81.92.0

LOWER MARBLE CANYON GAGE

GRAND CANYON GAGE

β

FINING COARSENING

CALENDAR YEAR

250-700 m3/s DISCHARGE 

0.40.50.60.70.80.91.01.11.21.31.41.51.61.7

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

1.81.92.0

LOWER MARBLE CANYON GAGE

GRAND CANYON GAGE

β

FINING COARSENING

CALENDAR YEAR

>700 m3/s DISCHARGE 

p < 1 x 10-16

p = 3.8 x 10-12

p = 7.9 x 10-12

p = 0.36

p < 1 x 10-16

p < 1 x 10-16
0.1

0.20.30.40.50.60.70.80.9

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

CROSS-SECTIONAL MEAN D50 OF 

SAND ON CHANNEL BED (mm) 

CALENDAR YEAR

LOWER MARBLE CANYON GAGE

0.10.20.30.40.50.60.70.80.9

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

CROSS-SECTIONAL MEAN D50 OF 

SAND ON CHANNEL BED (mm)

CALENDAR YEAR

GRAND CANYON GAGE

19% COARSER 

p = 2.4 x 10-7

11% COARSER 

p = 0.0073
0.10

0.150.200.250.300.35

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

MEAN D50 OF SAND ON SURFACE OF 

EDDY SANDBARS (mm)

CALENDAR YEAR

0.5 1.0 1.5 2.0 2.5 

0.00.10.20.30.40.50.60.70.80.91.0

RIVER-MILE 4RIVER-MILE RIVER-MILE RIVER-MILE 

SAND D

50

 NORMALIZED BY SAND D50 AT BASE OF DEPOSIT 

LINE OF ZERO GRAIN-SIZE CHANGE

NORMALIZED HEIGHT WITHIN DEPOSIT

(measured from base to top)
Idealized from Rubin et al. (1994) and Barnhardt 
Conclusions

• β-analyses of suspended-sediment data can be used in co

analyses of surface grain-size data to deduce which envircomplicated setting are the most important environments transport, regardless of whether these environments comor small part of the total environment

• In the case of the sand-supply-limited Colorado River in M

Grand Canyons, the bed environment that is the dominantransport in the river over multi-year timescales, the eddy comprises only a small percentage (~20%) of the total areeddies also dominant storage environment in post-dam riv

• 30-40% fining in eddy sandbar surfaces between 1986 an

corresponds to a factor of two increase in the concentratioover these sandbars (Topping et al., 2000)

• Increase in flux over the eddy-sandbar surfaces as the ba

lead to greater deposition and erosion rates in the eddies 

details of the flow fields in the eddies (Schmidt et al., 1993

2003; Nelson and McDonald, 1995; Rubin et al., 1998; W