Figure 6. Velocities, cm/sec, at Transect 6 (positive going south, negative going north)

ERDC TN-DOER-E7

April 2000

Figures 4 through 6 shows where the Wheeler crossed the transect. It can be seen in Figure 6 that

the flood currents, which generally extend from the bottom up to a depth of about 6 m, appear to

extend up to the surface in the vicinity of the Wheeler.

Figure 3 shows Transect 2, which was run just prior to the start of dredging operations. The transect

is shown from north to south and is along the eastern side slope of the channel (Figure 2). ABAB

is shown at a location where the Wheeler had turned to the west to reverse its direction and head

down the channel. The ABAB observed on this transect is believed to be a result of air bubbles

introduced into the water column from cavitation by the Wheeler's screws and rudder.

Figure 4 shows Transect 6, which was run close behind the Wheeler while it was dredging. The

transect is displayed from west to east. The area of the largest amount of ABAB is at about the 4-m

depth. This is approximately the location of the Wheeler's screws, and is believed to result from

cavitation. Cavitation around the drag arm assembly going from the Wheeler to the bottom may be

responsible for some of the ABAB shown in that region; however, ABAB near the bottom under

the Wheeler is probably all due to suspended sediment resulting from the dredging. Bottom-surge

currents created by the pressure wave emanating from the passing dredge may have stirred up bottom

sediments along the channel side slopes, and may be responsible for the ABAB shown there. Near

the surface to the right of the Wheeler, ABAB is shown that is believed to be from suspended

sediment released at the surface when the Wheeler pumped some residual water from its hopper just

before it began dredging. The plume from the sediment in that water would be going down the

channel with the Wheeler as the ebb currents in the surface layer carried it.