sediment accumulation due to channel infilling is thereby estimated to be
100 cu yd/year. This estimate corresponds well to volumes dredged in recent
times. The total rate of shoaling within the study area is estimated to be
1,280 cu yd/year, with the greatest amount of shoaling (1,180 cu yd/year)
occurring along the channel walls.
The total flood shoal volume was estimated with the empirical relation of
Carr de Betts (1999). Because the channel at Mattituck Inlet is constricted
compared to a relatively open bay, and there are no other recognizable areas of
shoaling, the near-field flood shoal volume predicted was considered appropriate.
Applying a tidal prism of 4.32 107 cu ft, the total volume of the flood shoal
was calculated to be 4.33 105 cu yd, and the total flood shoal area was
calculated to be 5.50 106 sq ft.
The empirical relation predicts a value that is larger than the directly
estimated volume by a factor of 10. Four reasons can be given for this large
difference:
a. The tidal current at Mattituck Inlet is weak compared to typical Florida
inlets where Carr de Betts (1999) performed her studies, and weak in
general compared to other permanent inlets. A weaker flood current
implies weaker transport and a smaller flood shoal.
b. The sediment on the beaches adjacent to Mattituck Inlet contains a large
coarse fraction as opposed to the homogeneous fine sand on Florida
beaches. Therefore, a smaller amount of fine material of the total
sediment load is available to be transported to the interior channel at
Mattituck Inlet.
c. Longshore sediment transport rates along the Atlantic coast and Gulf
coast of Florida exceed the estimated transport rates along the north
shore of Long Island by a factor of as much as 10, and 2 to 5 (including
hurricanes), respectively, again indicating less material is brought to the
inlet entrance and available for transport into the inlet.
d. Portions of the flood shoal in and around the navigation channel are
dredged.
Goldsmith Inlet
Similar to the situation of Mattituck Inlet, Goldsmith Inlet is in the low-tide-
dominated inlet classification range according to Davis and Hayes (1984)
(Figure 6-1). In contrast to Mattituck Inlet, Goldsmith Inlet does not fit the
description of a tide-dominated inlet identified by Hubbard et al. (1979). The
morphology of Goldsmith Inlet is more similar to that of a wave-dominated inlet,
having no apparent ebb-tidal shoal and a well-developed flood shoal. Because of
the strong direction of net longshore transport to the east and the coarse sand and
gravel predominant at the site, it is inferred that sediment bypasses the inlet
relatively close to shore, typically within the swash zone.
Table 6-5 lists r-values for Goldsmith Inlet and the quantities entering the
calculation. The surface area of Goldsmith Inlet and Pond was found to be 9.5
105 sq ft interpreted from GIS analysis of an aerial photograph dated 16 April
2003. The spring tidal range within the pond was calculated to be 3.2 ft based on
the water-level data collected 19 September to 8 October 2002. As with
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Chapter 6 Inlet Morphology and Stability
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