stabilization, lower and upper values for DA (x) were estimated based on the ocean and bay
values. Specifically,
Barrier Ocean Shoreline: B(x) =3.5 m relative to National Geodetic Vertical Datum
(NGVD) and DC (x)=-7.0 m NGVD
Barrier Bay Shoreline: B(x) =1.5 m NGVD, and DC (x)=-2.0 m NGVD
Montauk Bluffs Alternative 1: B(x) =3.5 m NGVD, and DC (x)=-7.0 m NGVD
Montauk Bluffs Alternative 2: B(x) =1.8 to 26.5 m NGVD, and DC (x)=-7.0 m
NGVD. Note that if the shoreline fronting the bluffs was accretional during a
particular time period, DA(x) = 10.5 m was applied. (i.e., the bluff was not "re-
created" during periods of accretion).
ANALYSES
Contribution of Montauk Point Bluffs
Two sediment budget Alternatives were evaluated to determine the potential
contribution of the Montauk Point bluffs to the littoral system. Alternative 1 implied that
the bluffs were an insignificant source of littoral material (0 m3/yr). Alternative 2 used the
bluff crest elevation to determine the active depth for an erosional shoreline. Assuming that
the bluff material is entirely littoral material (sandy), Alternative 2 results in bluff source
values equal to 62,000 m3/yr (1979 to 1995) and 66,200 m3/yr (1983 to 1995). Based on
sieve analysis data for the Montauk Point bluffs (personal communication, Henry
Bokuniewicz, 1999), approximately 63-percent of the size fraction (by weight) falls within
the "fine sand" (0.125 mm) to "coarse sand" (1.0 mm) range based on the Wentworth soil
classification. For formulation of Alternative 2, a conservative value of 50-percent littoral
material was applied to the Montauk Point bluff region, resulting in a littoral material
contribution ranging from 31,000 to 33,100 m3/yr. The final regional sediment budget was
developed by assuming a mean bluff contribution equal to 33,000 m3/yr, with an uncertainty
(based on values from earlier studies, see Table 1) equal to + 33,000 m3/yr.
Democrat Point Spit Growth Prior to Stabilization
Spit growth rates and net transport rates in the vicinity of Fire Island Inlet were
estimated using Fire Island Inlet bay and ocean shoreline position data prior to stabilization.
Pre-stabilization data are dated 1870, 1887, 1933 (no months available), and October 1938.
A location 14.1 km east of the present-day inlet represents a relatively stable portion of the
barrier island, as opposed to the migrating spit. Spit growth most likely included many
littoral processes that occurred in the vicinity of the inlet, e.g., net and gross LST, which
varied through time as the shoreline changed orientation; and onshore movement of the ebb
shoal as it was abandoned due to the westward movement of Fire Island Inlet. Thus, an
approximation of net LST was estimated at 14.1 km east of the inlet. Net LST at this
location averaged 159,000 + 72,800 m3/yr (DA=7 m) to 238,000 + 35,300 m3/yr (DA=10.5 m).
Impoundment rate at Democrat Point
Using data for nine profiles provided by Taney (1961a), the impoundment rate at the
East Fire Island Inlet jetty from 1940 (immediately after construction; jetties were
constructed from 1939 to 1941) to 1954 (estimated date of full impoundment) was
calculated as 385,000 m3/yr (Table 1). Assuming that the jetty was a total barrier, this rate
Rosati et al.
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