ERDC/CHL CETN-IV-27
September 2000
Sediment Transport (ft^3/s/ft)
0.00600
0.00560
0.00520
0.00480
0.00440
0.00400
N
0.00360
0.00320
0.00280
0.00240
0.00200
0.00160
0.00120
0.00080
0.00040
0.00000
3
Figure 13. Contours of sediment transport overlaid with sediment transport vectors (units in ft /s/ft) (To
convert cubic feet per second to cubic meters per second, multiply by 0.02831685)
The vector data set is constructed in the same manner as the shear stress vector data set. First,
one must assume that sediment transport acts in the same direction as the velocity. Next, the
velocity vector data set is reduced into velocity-magnitude and velocity-direction scalar data sets.
Finally, the velocity direction and sediment transport magnitude scalar data sets are combined to
construct the sediment transport vector data set.
Figure 13 makes apparent regions of considerable sediment transport (in red). Again, the plot
highlights the same regions as in previous plots at the north and south extremes of the channel
over the western shoal and over the outer bar of the ebb shoal. In interpreting sediment transport
plots, one must read the gradients of sediment transport in the direction of sediment transport to
infer bed elevation change. For example, as water flows from regions of weak sediment
transport to regions of strong sediment transport, scouring of the bed occurs in the region of
strong sediment transport because more sediment leaves the area downstream than enters from
upstream. Conversely, as water flows from regions of strong sediment transport to regions of
weak sediment transport, deposition occurs in the region of weak sediment transport because
more sediment enters the area from upstream than leaves downstream. From the figure, the red
region over the ebb shoal bar should experience erosion because the sediment-transport gradient
increases in the flow direction. South of this point, an area of deposition should occur because
the sediment-transport gradient decreases in the flow direction. The net effect is an offshore
translation of the ebb shoal bar.
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