WSP09211

• File Number: 8220.101.10
• Description: Colorado River-Water Projects-Glen Canyon Dam/Lake Powell-Glen Canyon Adaptive Management-
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/2005
• Author: Wiele-Torizzo
• Title: Modeling of Sand Deposition in Archaeologically Significant Reaches of the Colorado River in Grand Canyon
• Water Supply Pro - Doc Type: Report/Study

...

368 Computational FllIid Dynamics

100

Sand discharge e
. Low sand supply
. Intermediate sand supply .
r 0 . High sand supply
... '.
.
..
r . Grain size
o low sand supply L:.
~ <- Intermeaiate sand supply
. ~ High sand supply

0.30 .
0.25
E
g
"
0.20 N
in
"
'"
i5
0.15

~
110
"
'"
~
i;l
o
"
"
'"
rJl

0.1 I
1000 1500
1270

2000 2500

0.10
3000
2830

Water discharge (mJ/s)

Figure 14.4 S~lnd discharge Jnel grain size as functions of waler discharge lor three sand
conditions u!ied as boundary conditions for the model runs: high sand supply during 1956,
;ntermedi,lte !i.md .wpply repr~!iented by the conditions during the 1996 test ,Jaw Clnd low
.(,and supply dllrin.~ 1983. The.f;e VJJut'~ for sand discharge clnd grain ...ize were contributed by
Tvpping fUSGS, written commllnication, /998J.

representative of historical high sand supplies. historical low sand supplies and an
intermediate condition corresponding to that which occurred during the 1996 test
tlow. The historical high sand supply corresponds to conditions represented by
measurements in 1956. prior to the dam construction. Th~ historical low was taken
from sand conditions in 1983. after the dam had been eliminating main channel
inputs for nearly 20 years and during flows approaching 2830 m.l/s. These two
conditions, high discharge and low sediment supply. combined to winnow the bed
to a Coarser state and thereby reduce suspended sand transport (Topping etal..
2000a,b). The 1996 sand conditions are representative of typical <:ontemporary
conditions. The llpstream sand boundary conditions corresponding to the three
sand sllpplies were taken from sand rating curves supplied by David J. Topping
(liS Geological Survey. written communication. 1998). Topping 11997) related sand
concentralions and sand sizes to antecedent conditions and the evolving status of sand
on the channel bed. which forms the source from which sand in suspension is derived.
One of the initial conditions that must be specified is the sand coverage on the bed
at the start of the simulation. Previous model applications have been in reaches in
"hich bathymetric measurements have been repeated. allowing for tbe estimation of
a minimum bed elevation by combining the lowest elevations from different surveys.
Another approach in modelling events in which the change in sand deposits is
dominantly depositional. and where there is insufficient information to synthesize
a minimum bed elevation, is to neglect erosion and make the starting bed shape the
minimum hed elevation. In this study. the local initial sand conditions on the bed
were estimated by running the model in each reach at a discharge characteristic of
dam operation 1~81 m'is was chosen for these simulations) with a sand boundar~

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