1,020 sq ft
Figure 6-5. Escoffier curve calculated for Mattituck Inlet, CEA model
The Jarrett (1976) relation predicts an msl minimum stable channel cross-
sectional area of 1,035 sq ft for Mattituck Inlet. The Escoffier analysis of
Mattituck Inlet predicts a stable channel cross-sectional area of 1,020 sq ft, which
is 36 percent smaller than the observed October 2002 measurement of
1,600 sq ft.
The measured inlet channel cross-sectional area is significantly larger than
predicted. The Escoffier stability analysis is based on the implicit assumption
that the bay tide range will approach or equal the ocean or forcing tide range
(Seabergh 2003). This is not the case for Mattituck Inlet, yet the channel cross-
sectional area is greater. Such a morphological property, a much larger-than-
predicted inlet channel cross-sectional area, is anomalous.
Several factors might contribute to the unusually large channel cross-
sectional area. In the judgment of the authors, in possible order of significance,
a. Historic mining of the inlet channel and the adjacent west beach may
have removed at least 500,000 cu yd of sand and gravel over an
approximate 50-year period (1920s to 1970s), artificially increasing the
area and hydraulic efficiency of the entrance channel.
b. The relatively low longshore sediment transport rate found on the north
shore of Long Island and at this site, due to its shoreline orientation and
protection by the west jetty, is not adequate to fill a maintained channel.
c. The relatively small W/D ratio of 43, indicating hydraulically efficient
inlet (for fine-and medium-sized sand).
Mattituck Inlet offshore shoal
To further explore the origin of the linear offshore shoal located east of
Mattituck Inlet, that is, whether or not it is an ebb-tidal shoal, the empirical
Chapter 6 Inlet Morphology and Stability