has increasingly returned to a natural condition, where the inlet entrance is
oriented at an acute angle in relation to the shoreline.
Multiple (typically, two or three) longshore bars are prominent to the west of
Mattituck Inlet, but bars are absent west of Goldsmith Inlet, perhaps owing to a
depression in the nearshore located just west of the jetty. Significant longshore
bars are not found along the beaches directly to the east of the inlets. The
shorelines to the west of both inlets have advanced considerably through
impoundment at the west jetties, as compared to the position of the respective
shorelines to the east, which receded after construction of the jetties at both
locations. The shorelines to the west of the inlets are considerably smoother than
the shorelines directly to the east. Material dredged as part of Federal navigation
project channel maintenance prior to the dredging of 1946 was probably placed
offshore. Condition surveys and dredging records indicate that material dredged
in 1946 and later, with the exception of the dredging of 1961, was placed on the
downdrift beach or in the nearshore of the downdrift beach.
Hydrodynamics and tidal shoals
The tidal prism at Mattituck Inlet is about 14 times greater than that at
Goldsmith Inlet. However, the maximum current velocity through the mouth of
Goldsmith Inlet can exceed 1 m/sec, whereas at Mattituck Inlet the current
between the jetties rarely exceeds 0.5 m/sec. Numerical modeling of Mattituck
Inlet in a representative natural condition (nineteenth century) indicated a
maximum current exceeding 1 m/sec, similar to that at Goldsmith Inlet. Despite
the great differences in tidal current, both inlets share geomorphic commonality
in possessing flood shoals composed of fine-to-medium sand, and each lacks an
ebb shoal.
Although the maximum ebb-current velocity at Goldsmith Inlet exceeds
1 m/sec and is comparable to that at other inlets that have formed ebb-tidal
shoals, the volume of water flow or discharge is evidently too small to construct
an ebb shoal. Sediment transported by the ebb current to the mouth of Goldsmith
Inlet is moved away from the entrance by waves and the wave-induced longshore
current.
Strong flood dominance exists at Goldsmith Inlet, which promotes
movement of sediment, particularly fine sand, toward Goldsmith Pond, creating
broad flood shoals. Numerical simulation of tidal hydrodynamics at Mattituck
Inlet with a configuration representative of conditions prior to jetty construction
indicates that this inlet was also flood dominant. Mattituck Inlet and Goldsmith
Inlet cannot support ebb shoals because the ebb current velocity at Mattituck
Inlet is too weak (maximum of 0.5 m/sec), and the discharge at Goldsmith Inlet is
too small.
Channel cross-sectional area stability
The minimum channel cross-sectional area for Goldsmith Inlet agrees with
the empirical prediction for small inlets in Chesapeake Bay (Byrne et al. 1980).
In contrast, the minimum channel cross-sectional area of Mattituck Inlet is about
one-third larger than the empirical prediction for Atlantic coast dual-jetty inlets
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Chapter 7 Comparative Analysis and Conclusions