where AFN = near field area of the flood shoal in square meters.
The regression correlations for these relations were weak. In contrast to an
ebb shoal, there is no significant wave force acting against the flood-tidal jet,
allowing sediment to travel far into an inlet and spread in a thin layer that is
difficult to measure. Older portions of flood shoals are difficult to distinguish
from peripheral wetlands and marshes. Flood shoals are also manipulated
through dredging. These empirical relations, however, can be useful in obtaining
order-of-magnitude estimates.
Mattituck Inlet
Material introduced in the preceding sections of this chapter is applied to
Mattituck Inlet in this section and to Goldsmith Inlet in the following section.
According to the classification by Davis and Hayes (1984), shown in
Figure 6-1, Mattituck Inlet is a tide-dominated inlet because it experiences
forcing by a diurnal mean tidal range of approximately 1.6 m and is subject to a
relatively small mean wave height. Given the limited fetch of Long Island
Sound, the mean annual wave height for non-calm events (when waves are
present) for Mattituck Inlet is estimated to be 0.3 m and consists mainly of steep
wind waves that would tend to move finer sand offshore (Batten and Kraus
2005).
Hubbard et al. (1979) classified tidal inlet morphology based on the
hydrodynamic setting. Tide-dominated inlets have well-developed ebb shoals,
and sand bypassing is accomplished through tidal bypassing. It has been
concluded in this study that the linear shoal located offshore of Mattituck Inlet is
not an ebb shoal. Evidence of tidal bypassing, however, can be seen in the depth
contours between this feature and the entrance channel (Figure 3-16).
Table 6-3 lists values to calculate the r ratio for Mattituck Inlet. The tidal
prism was calculated by multiplying the bay area of the inlet by its spring tidal
range. The surface area of Mattituck Inlet and Mattituck Creek was
7.2 106 sq ft as interpreted from GIS analysis of an aerial photograph dated 16
April 2003. The spring tide range within the creek was 6.0 ft based on water-
level data collected 19 September to 8 October 2002, consistent with the value
given by NOS for the area.
Because the gross longshore sediment transport rate at Mattituck Inlet is not
well known, two values (15,000 and 25,000 cu yd/year) were used to calculate
the r ratio of Mattituck Inlet. These values are considered to represent the
minimum and maximum gross longshore sediment transport rates at the inlet.
Mattituck Inlet has an r ratio of in the range of 64 to 107 (Table 6-3). According
to the classification of Bruun and Gerritsen (1959, 1960) summarized in
Table 6-1, inlets with an r ratio of 50 to 150 have a well-developed ebb shoal
(sandy beaches), and sand bypassing occurs through a combination of bar
bypassing and tidal bypassing. Mattituck Inlet lacks an ebb shoal. However,
sediment bypassing from the west beach may occur along the offshore shoal, and
it is inferred to occur along a bypassing bar located near the tip of the west jetty.
It is feasible that fine to medium sand can bypass in this way, but not coarser
sand and gravel because of the small waves and weak tidal current (Chapter 5).
The sand bypassing complex offshore of Mattituck Inlet is displayed in Figure 3-
271
Chapter 6 Inlet Morphology and Stability
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