WSP05649

• File Number: 8220.101.10.D
• Description: Glen Canyon Dam/Lake Powell
• State: AZ
• Basin: Colorado Mainstem
• Date: 2/1/2000
• Author: Topping et al.
• Title: Colorado River Sediment Transport
• Water Supply Pro - Doc Type: Report/Study

TOPPfNG ET AL: COLORADO RIVER SEDIMENT TRANSPORT, 2

563

10

RIVER MILE 28.5

100

lJl
~
o
~
;;
;;::
*

0.1

0.01

0.001

0.05

0.1

-0- 3-98 (0.59 nm)
---.- 8-68 (0.46 mm)
-lIl- 5-99 (o... nwn)

0.5

1.0

20

100
lJl 10 SECONDARY MODE
~ \
0
I!l
;; 0.1
;;:: --0-- 3-98 (0.45 mm)
.. 0.01 --+- 9-98 (0..... nvn)
-lIl- 5-99 (0.32 mm)
0.001
0.05 0.1 0.2 0.5 1.0 2.0
GRAIN SIZE (nm)
100 RIVER MILE 50.1
~ 10 -<>- 3-118 (0.32 mm)
__.... (0.33 mm)
-lIl- 5-99 (0.42 mm)
" SECOND~Y MODE
I!l
;; 0.1
;;::
* 0.01
0.001
0.05 0.1 0.2 0.5 1.0 2.0
GRAIN SIZE (11lTl)
100
~ 10 -<>- 3-.. (0.43 mm)
__"98 (0.33 mm)
" -lIl- 5-99 (0.38 mm)
w
N
<ii 0.1
;;::
* 0.01
0.001
0.05 0.1 0.2 0.5 1.0 2.0
GRAIN SIZE (nwn)

Figure 14. (continued)

where 1} is the elevation of the bed, Cb is the concentration of
sediment in the bed. VI" is the volume of sediment in suspen-
sion, and Q. is the flux of sediment.
Changes in the volume of sediment in suspension with re.
spectto time (~V,/~I) are driven primarily by changes in the
boundary shear stress at a given location over time. Colby
(1964] demonstrated that in a typical sand-bedded river, the
magnitude of bed scour and fill related to temporal changes in
the volume of suspended sediment during a flood (i.e., ~ V,I al)
is small. As noted by Rubin and Hunter (19821, the volume of
sediment available for deposition in response to iJVsliJl is
limited to the volume of sediment in transport over the depo-
sitional site on the bed. In contrast, when the volume of sed-
iment in transport decreases in the downstream direction, the
volume of sediment availa.ble for deposition includes all of the
upstream sediment in transport. Thus, in most situations, the
portion of scour and fill driven by V . Qs dominates over the
portion of scour and fill driven by aVslat. Indeed, in {he case

of the 1996 Grand Canyon flood experiment, only 1 cm of bed
scour althe Grand Canyon cableway would be needed to equal
the measured increase in the unit volume of sediment in sus-
pension during the rising limb of the flood. However, while this
maximum of 1 ern of bed scour could have occurred in re-
sponse to ~ V,I ~I during the rising limb of the flood, the bed at
the Grand Canyon cableway aggraded by 0.5 m in response to
V'Q,.
Divergence in the flux of sediment (V ' Q,l can be driven by
either reach-geometric effects, changes in the magnitude of the
upstream sediment supply, or both. For example, given a con-
stant upstream supply of sediment, streamwise divergence in
the flux of sediment at a cross section can be caused purely by
reach-geometric effects if, given a change in water-sudace
stage, the sediment-transport rate at that cross section in-
creases faster than the sediment-transport rate at the cross
section ups[ream. Conversely, a decrease in the upstream sup-
ply of sediment will also rcsuh in streamwise divergence in the