A comparison was also made of mean velocities within the rip channel obtained
from both an array of current meters and the method of VDT for the long tests. Table 3-4
shows the number of discrete drifter velocity measurements used to obtain the mean
velocity in the rip channel for the method of VDT. The current meter and VDT window
locations within the rip channel, shown in Figure 3-19, are the same as the comparison
made for the transient tests. In Figure 3-21 (a), the mean cross shore component of
velocity obtained from VDT for the long tests was corrected for Stokes drift, which
decreased the root mean square (RMS) of the error from 6.81 cm/s to 3.30 cm/s. The
RMS of the error for the longshore component of velocity was 1.84 cm/s. This shows
adequate agreement between the mean velocities obtained from the current meters and
the method of VDT for the long tests.
0 10
(a) (b)
-50
o 5-
0 0
-10 9 o0
E 0 E
x 7
o -15 o O
x -5
-20 x
-25 -10
-25 -20 -15 -10 -5 0 -10 -5 0 5 10
Current Meter (cm/s) Current Meter (cm/s)
Figure 3-21: Comparison of mean velocity between VDT and Current Meters within the
rip channel for the long tests / (o) Before Stokes drift correction to VDT
measurements; (x) After Stokes drift correction to VDT measurements / (a)
Cross shore velocity; (b) Longshore velocity