located near msl. At the lower water levels of ebb tide, the sills at the flood shoal
and shoreline become more effective in retarding flow. In addition, water enters
the fringing marsh of Goldsmith Pond on flood tide more rapidly than when it
exits on ebb. The effective friction of the marsh, creating storage capacity, will
release water slowly as compared to its entrance at flood tide.
The mouth of Goldsmith Inlet appears to be at or near locational equilibrium
if it is oriented to the east. Past dredging practice has realigned the channel
parallel to the jetty. It is hypothesized here that an orientation with the mouth
directed to the east is the optimum for sediment bypassing and maintenance of
inlet stability. The attached fillet to the east, between the jetty and the inlet
mouth, now functions to bypass sediment via transport in the swash zone.
If the accretion fillet to the west were mined substantially, impoundment at
the jetty would reduce the sediment bypassing volume, turning back the
processes in time.
Recommendations for Future Studies
Wave measurements are lacking for the Long Island Sound and are essential
for improving the reliability of coastal studies both for Long Island and
Connecticut. Long-term measurements will allow development of a wave
hindcast needed in engineering design. The USACE, New England District, and
the New York District could share costs and benefits of wave gauging. At
present, the University of Connecticut operates a nondirectional wave gauge in
the middle of Long Island Sound. This gauge could be upgraded to directional
capability for modest cost.
The amount of sediment that may be directed offshore by jetties along the
north shore of Long Island is unknown. Because of the steep nearshore slope and
coarse material, material directed offshore will not return to the beach. Offshore
movement of sediment is an unanswered question, and it may be related to the
observed reduction in required dredging volume at Mattituck Inlet. It was
beyond the scope of this primarily morphologic study to apply a combined wave,
current, and sediment transport model to estimate offshore sediment transport.
Also, wave data are lacking to drive such a model.
It is recommended that sediment sampling be conducted in the offshore area
of jetties to determine sediment texture and, as necessary, high-resolution
bathymetric surveys be made to detect sediment buildup offshore. These might
be done in conjunction with channel condition surveys.
The rate of channel infilling at Mattituck Inlet is low as compared to early in
the twentieth century, indicating efficient protection by the jetties in their present
configuration. Maintenance dredging removes the portion of the flood shoal that
encroaches upon the Federal navigation channel. This formation has never been
dredged in its entirety. Full removal of the portion of this shoal lying outside the
navigation channel would greatly reduce shoaling at Mattituck Inlet and increase
the required time interval between maintenance dredging, while supplying
material to the downdrift beach. The volume of material that could be provided
is estimated to be on the order of 15,000 cu yd, comparable to that removed from
the channel during the typical 10-year dredging cycle. This feature appears to
function as a groin in accumulating sediment, promoting channel bank
295
Chapter 7 Comparative Analysis and Conclusions
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