predominantly of gravel and trends towards fine gravel to coarse sand proceeding
south into the inlet. The difference in grain size distribution patterns observed is
attributed to the difference in inlet width. At Mattituck Inlet, wave action has
potential to transport coarse-grained sediment into the inlet. In contrast, the
narrow width at Goldsmith Inlet prevents large waves from entering the inlet.
Coarse-grained sediment is, therefore, not redistributed and remains at the inlet
entrance.
The absence of ebb shoals at Mattituck Inlet and Goldsmith Inlet
distinguishes them from the inlets on the south shore of Long Island (as well as
from other tidal inlets on alluvial coasts), which possess ebb shoals with volumes
in the range of about 8 to 40 million cu yd. Absence of an ebb shoal is a shared
feature with harbors and entrances in the Great Lakes of the United States.
Anthropogenic influences
Although Mattituck Inlet and Goldsmith Inlet have similar forcing and
geologic setting, there are substantial distinguishing physical characteristics.
Two jetties built approximately 100 years ago have been maintained and
improved to support shallow-draft navigation protecting Mattituck Inlet.
Mattituck Inlet has been dredged extensively, possible to as deep as 20 ft mlw in
certain locations of the Federal navigation project by commercial mining
interests. Commercial mining took place on the beach directly west of the west
jetty between 1960 and 1975 (and probably earlier) as well. Combined, it is
estimated that these activities removed an estimated 500,000 to 900,000 cu yd of
sediment from the inlet and littoral system between the 1920s and 1970s.
Material dredged as part of the Federal navigation project prior to the 1946 was
probably placed offshore (and could feasibly have contributed to the volume of
the offshore shoal located east of the inlet), whereas material dredged between
the 1960s and present has been placed on the downdrift beach.
The jetties at Mattituck Inlet are 400 ft apart, and the navigation channel is
100 ft wide at the bottom, maintained to a minimum depth of 7 ft mlw plus 2 ft
allowable overdredging. The width of Goldsmith Inlet varies and is typically on
the order of 25 to 75 ft, depending on the stage of tide. Two jetties fix the
location of Mattituck Inlet, whereas the entrance to Goldsmith Inlet can migrate
to the east, in the direction of net longshore sediment transport induced by
breaking waves. There is geomorphic evidence that the mouth of Mattituck Inlet
migrated west prior to construction of the jetties, but would return to its root
channel, Mattituck Creek. Typical greater depths at Mattituck inlet range
between 7 and 18 ft, mlw, whereas typical greater depths at Goldsmith Inlet
range between 2 and 4 ft mlw.
The jetty at Goldsmith Inlet was constructed 40 years ago (1964) and is not
maintained. The jetty functions as a sediment-retention structure or groin,
serving no navigation purpose. The structure can be termed as a jetty only in
historic context as part of a marina-development plan that was not implemented.
Goldsmith Inlet has been dredged or excavated intermittently and shallowly (to
maximum depth of about 3 ft mlw) in the past half century. Material dredged
from Goldsmith Inlet since the 1970s has been placed on the downdrift beach.
Because the jetty at Goldsmith Inlet has reached impoundment capacity, the inlet
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Chapter 7 Comparative Analysis and Conclusions
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