Since closure of Glen Canyon Dam in 1962, the supply of fine sediment to the Colorado River in Grand

1
H13E-1369
Large-Scale Sediment Routing Development of a
One-Dimensional Model Incorporating Sand
Storage Stephen Wiele1, Peter Wilcock2, and Paul
Grams2 1 USGS Water Science Center, Tucson, AZ,
smwiele_at_usgs.gov 2Johns Hopkins University,
Baltimore, MD, wilcock_at_jhu.edu ,grams_at_cc.usu.edu
Introduction Since closure of Glen Canyon Dam in
1962, the supply of fine sediment to the Colorado
River in Grand Canyon has been severely reduced.
One of the impacts of the post-dam sediment
budget is a decline in the size and abundance of
eddy-deposited sand bars. The Grand Canyon
Adaptive Management Work Group seeks to manage
Glen Canyon Dam operations, within other
operational and environmental constraints, to
restore and maintain sand bars with sand
contributed by tributaries. In support of river
management efforts, we have developed a
large-scale one-dimensional model of unsteady
flow and sand transport to route sand downstream
from Glen Canyon Dam to Phantom Ranch, about 100
miles downstream. Model applications can address
several significant management issues (1) the
potentially rapid migration of tributary sand
inputs through the system, which has important
implications for the engineering and
institutional basis for dam operations (2) the
effect of timing, magnitude, and duration of
dam-release alternatives on building sand bars
and (3) the linkages between dam operations, sand
deposits, and the biological, recreational, and
archaeological resources along the river
corridor.
Model development presents two main challenges
1) How to account for spatial variations in sand
transport and storage? a) One-dimensional
models cannot directly account for exchange of
sand with side-channel environments. b)
Multi-dimensional models have large computational
and data requirements. We developed a 1d model,
but separate the sand routing and storage
calculations
2) How can suspended sand transport over a gravel
bed be calculated?
Conventional algorithms for suspended sand
transport are not appropriate where sand on the
bed is in the interstices of gravel.

Results from a 2.5d model of flow, sand
transport, and bed evolution (Wiele and Torizzo,
2005) was applied to kilometer-scale reaches and
the results incorporated into the 1d model. The
1d model accounts for sand into and out of eddies
as a function of sand volume in the eddy, sand in
transport, water discharge, and reach-averaged
eddy characteristics as determined by the 2d
model.
Flume experiments and analysis of flume data
produced a function for near-bed sand
concentration over a bed of exposed gravel (Grams
and others, 2005). With the near-bed
concentration, a Rouse profile can be used to
calculate local transport.

Model application Sand supplied by the Paria
River near river mile 0 triggered a release
pattern designed to make best use of available
sand for restoring sand bars. Low fluctuating
flows in the fall of 2004 were followed by a
release of about 42,000 cfs in November 2004. The
high flow was followed by several days of steady
8,000 cfs and then a resumption of fluctuating
flows. The 1d model was applied to these flows
starting September 1, 2004 and continuing to
March 1, 2005. Discharge from the Lees Ferry gage
(rm 0) and sand inputs from the Paria River and
the Little Colorado River determined form gage
discharge data and sediment transport models
(Topping, 1997) were used for the upstream
boundary conditions. Model results were
compared to sand flux measured at rm 30, 61, and
87, and to eddy sand volumes measure by the
Northern Arizona Sand Bars Studies and analyzed
by M. Breedlove (Utah State University).
Hydraulic geometry is represented by
reach-averaged channel properties based on cross
sections at 80m intervals from continuous
topography above the 8,000 cfs water surface (M.
Breedlove, Grand Canyon Monitoring and Research
Center), cross sections measured about every mile
(Wilson, 1986), a dye study at 15,000 cfs (Graf,
1995), average channel shape (using a method
similar to Griffin, 1997), and stage-discharge
relations using the method of Wiele and Torizzo
(2003). Local discharge is calculated with an
unsteady flow model (Wiele and Smith, 1996 Wiele
and Griffin, 1997).
References Graf, J.B., 1995, Measured and
predicted velocity and longitudinal dispersion at
steady and unsteady flow, Colorado River, Glen
Canyon Dam to Lake Mead Water Resources
Bulletin, v. 31, no. 2, p. 265281. Grams, P.,
Wilcock, P. R., and Wiele, S.M., 2005, A
formulation for fine sediment in coarse-bedded
rivers. This meeting H53B-0464. Griffin, E.R.,
1997, Use of a geographic information system to
extract topography for modeling flow in the
Colorado River through Marble and Grand
Canyons Boulder Colorado, University of
Colorado, unpublished master's thesis, 113
p. Topping, D. J. 1997. Physics of flow, sediment
transport, hydraulic geometry, and channel
geomorphic adjustment during flash floods in the
ephemeral river, the Paria River, Utah and
Arizona. Dissertation. University of Washington,
Seattle, Washington, USA. Wiele, S.M. and Smith,
J. D., A reach-averaged model of diurnal
discharge wave propagation down the Colorado
River through the Grand Canyon, Water
Resources Research, 32(5), 1375-1386,
1996. Wiele, S. M. and Griffin, E.R., 1997,
Modifications to a one-dimensional model of
unsteady flow in the Colorado River through the
Grand Canyon Water Resources Investigation
Report 97-4046. Wiele, S.M., and Torizzo, M.,
2003, A stage-normalized function for the
synthesis of stage-discharge relations for the
Colorado River in Grand Canyon, Arizona,
USGS Water-Resources Investigations Report
03-4037. Wiele, S.M. and Torizzo, M., 2005,
Modelling of sand deposition in archeologically
significant reaches of the Colorado River in
Grand Canyon, USA, Bates, P., Lane, S.,
and Ferguson, R. (eds.) Computational Fluid
Dynamics Applications in Environmental
Hydraulics John Wiley and Sons, West
Sussex, England. Wilson, R.T., Sonar patterns of
Colorado River bed, Grand Canyon, Proceedings of
the Fourth Federal Interagency Sedimentation
Conference, 2, 5- 133 to 5-142, Las Vegas,
Nevada, 1986.