most likely represents a high estimate of the net LST rate, for reasons as cited by RPI
(1983; see previous summary) and possible accretion due to onshore welding of the eastern
portion of the Fire Island ebb shoal.
Potential Longshore Sand Transport Rate Calculations
Net, left-, and right-directed LST rates were calculated from Fire Island to
approximately 6 km west of Montauk Point using the Wave Information Study (WIS) 1976-
1994 hindcast database, with adjustments made based on comparison to measured wave
data at two locations (offshore of Westhampton and Fire Island). Potential LST rates were
calculated by transforming the adjusted wave database over the nearshore bathymetry. The
transport rate coefficients were adjusted such that the magnitude of the potential transport
rate agreed with accepted rates at Fire Island Inlet. These coefficients (K1=0.2, K2=0.15;
see Gravens et al. 1999 for details) were held constant for the entire study domain. Results
were applied in formulating the regional sediment budget. Specifically, magnitudes of the
net LST rate as determined by the sediment budget were checked against the potential net
LST rate calculations and modified, if appropriate. In addition, the standard deviation in
the 19-year time series was applied to develop uncertainty limits for the regional sediment
budget.
Beach Loss due to Relative Sea Level Rise
The rate of relative sea level rise, as estimated from 90 years of tidal records at the
Battery in New York City, was 0.003 m/yr. The long-term beach loss due to an increase
in relative sea level was calculated (Bruun 1962) as 0.16 m/yr for the Montauk Reach and
0.19 m/yr for the Westhampton and Fire Island Reaches. Montauk Reach had a lower
value due to a steeper profile shape as compared to the remainder of the study area. This
rate was converted to a volumetric loss and was applied to all ocean shoreline cells within
the sediment budget.
Wind-blown Sand Transport
Gains and losses due to wind-blown sand transport can be a contributing factor to the
observed shoreline position. Onshore-directed winds can remove sand from the shoreline
as wind-blown sand transport creates dune features. In fact, this process was an active
contributor in rebuilding dunes that were entirely lost during the "Ash Wednesday" storm
in 1962. By 1979, onshore wind-blown sand transport and beach fill placement had
completely rebuilt the dune system. Since 1979, the dune system has been fairly well-
established and vegetated. Conversely, offshore-directed winds can remove sand from the
beach. For the regional sediment budget, which represents sediment transport and
engineering activities within the 1979 to 1995 period, dune growth has been minimal. Thus,
the contribution of wind-blown sand transport was assumed to be minor.
Inlet Sediment Budgets
Inlet sediment budgets representative of the 1979 to 1995 period were formulated using
shoreline position data, bathymetric data, dredging and placement history, and knowledge
of the site. Sources and sinks for each budget are detailed in the next section. Moffatt &
Nichol and URS Consultants (1999) present details of the inlet budgets.
CONCEPTUAL SEDIMENT BUDGET
Rosati et al.
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