Figure 5-18f. Near-maximum offshore ebb-tide velocity and depth, Mattituck
Inlet offshore shoal area, 1830 GMT on 7 October
Figure 5-18g illustrates current velocity at 2030 on 7 October 2002, the time
of near-maximum inlet ebb current. Figure 5-18h displays these same current
velocity vectors overlying the inlet and offshore shoal bathymetry. When the
current is at its peak of near 1.87 m/sec, current velocity magnitudes diminish
greatly with distance from the inlet entrance. The maximum tidal current
velocity at the western extreme of the offshore shoal is calculated to be
0.36 m/sec. Figure 5-19 illustrates the locations of the current velocities plotted
in Figures 5-20a and 5-20b, which include the offshore bathymetry. Current
velocities shown in Figure 5-20b are nearly equivalent and are, therefore,
difficult to discern.
For a configuration representing Mattituck Inlet in its natural state, prior to
stabilization by jetties, the depth-averaged ebb-tidal current velocity at the
offshore shoal is relatively weak, reaching about 0.35 m/sec for short durations.
Such a current velocity exceeds the threshold of motion for medium sand grains,
and the presence of wave orbital velocities near the bottom would further
mobilize sand and make it available for transport. The direction of the calculated
ebb current at maximum velocity is compatible with formation of an ebb shoal at
the general location of the offshore shoal. However, the highly linear shape of
the offshore shoal does not conform with the horizontal pattern of the ebb
current, which tends to expand in areas beyond the location of the offshore shoal.
Also, the relatively short duration when sand could be transported further
indicates that the offshore shoal is not a relict ebb shoal of the historic Matttituck
Inlet.
240
Chapter 5 Circulation Analysis
Previous Page
