General features of geomorphology

these inlets are 5.2 and 6.0 ft, respectively. Predominant waves are out of the

west, both in height and duration of incidence. Data are lacking on the wave

climatology of Long Island Sound with which to make quantitative predictions

with standard engineering formulas. The long-term net longshore sediment

transport is estimated to be 15,000 cu yd/year to the east at Goldsmith Inlet and

somewhat less at Mattituck Inlet, based upon impoundment rates at the jetties,

the orientation of the inlets relative to the predominant direction of wave

incidence, and consistency with dredging records. Batten and Kraus (2005)

obtained a net rate of 16,000 cu yd/year to the east at Mattituck Inlet and a gross

rate of 21,000 cu yd/year based on a sediment budget analysis.

Both inlets supported tidal mills in the 1700s and 1800s, owing to the

significant tidal range and relatively narrow channels. Therefore, in their natural

states, the inlets must have experienced substantial tidal flow much of the year,

although it is believed that the inlets would close temporarily due to presence of

ice in winter and by occasional blockage from longshore sediment transport.

General features of geomorphology

Mattituck Inlet and Goldsmith Inlet share similar geologic settings

characterized by coarse sediment and steep slopes, a result of the glacial origins

of Long Island and a terminal moraine (Harbor Hill Moraine) located near the

north shore. Each inlet lies at the center of a pocket beach bounded by

headlands, and the adjacent beaches, cliffs, and the neighboring coastal cliffs of

glacial origin are composed of a wide variety of grain sizes. Both inlets and their

back bays are likely low-lying watersheds created by glaciers, and these areas are

prone to sediment deposition.

The predominant grain size on the beaches and in the inlet entrances ranges

between medium sand to gravel. In their natural states, prior to construction of

jetties, the entrances to both inlets probably migrated moderately eastward (order

of tens of feet for Goldsmith Inlet and hundreds of feet for Mattituck Inlet),

returning to their root or original channel locations by breaking through the spit

formed as part of the migration process. Mattituck Creek bends to the west

before interrupting the dune line and exiting to Long Island Sound, suggesting

underlying geologic control (hard bottom) that prevents direct access to the

sound. A large number of glacial erratics can be observed in the nearshore on the

eastern side of Mattituck Inlet. Cross-sectional channel stability of Goldsmith

Inlet may also have been promoted by either a geologic control or structures to

the west of the present location of the inlet.

The area offshore (12-30 ft mlw) of each inlet is composed predominantly of

fine to medium grained sand. The offshore east of each inlet contains higher

percentages of medium grained sand than areas west. No offshore area contains

gravel, with the notable exception of the offshore shoal formation east of

Mattituck Inlet, which has a gravel content estimted at 31 percent. The

distribution of sediment grain sizes for the nearshore area west of both inlets is

bimodal, with large percentages of medium grained sand and gravel. The

nearshore area east of each inlet is composed predominantly of fine and medium

sand. The sediment in the Federal navigation channel at Mattituck Inlet is a

mixture of fine, medium, and coarse sand, and trends toward coarser material

proceeding into the inlet. At Goldsmith Inlet, the inlet entrance is composed

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Chapter 7 Comparative Analysis and Conclusions