from 76,000 to 123,000 m3/yr. This conceptual budget result is slightly high, but is
considered reasonable.
Fire Island Reach. Values applied in Eq. (1) result in a net LST rate 3 km east of Fire
Island Inlet equal to 349,000 m3/yr. The conceptual sediment budget result is within the
range of Taney' (1961a,b) proposed values; higher than the estimates based on the growth
s
rate of Democrat Point prior to stabilization; higher than RPI' (1983) sediment budget; and
s
lower than the rate estimated by Kana (1995). For the purposes of the conceptual sediment
budget, this result is considered within the range of accepted values. In addition, it is
concluded that the previous assumption of a net LST rate east of Shinnecock Inlet, which
was adopted from the potential LST calculations (115,000 m3/yr), was reasonable.
Formulation of a macro-budget is accomplished by combining all cells of the final
conceptual budget (Fig. 4). The macro-budget satisfies Eq. (1) with a residual of zero, a
final check prior to proceeding with the detailed budget.
REGIONAL SEDIMENT BUDGET
The regional sediment budget represents coastal processes, engineering activities, and
structure conditions reflected by the 1979 to 1995 period. The budget was developed using
the data and analyses discussed previously with equal weighting of the 1979 to 1995 and
the 1983 to 1995 sediment budgets. Bluff contribution Alternative 2 (33,000+33,000 m3/yr)
was applied. Uncertainties associated with net LST at each primary morphologic reach
were estimated based on the potential LST calculations. Specifically, following a procedure
discussed by Kraus and Rosati (1999), the standard deviation in the net LST rate was
divided by the square root of the number of yearly averages ( 29 ) to give a representative
decadal-scale variability. This value ranged from 30,000 to 40,000 m3/yr for the study area,
and a conservative value of uncertainty in the net LST rate equal to 40,000 m3/yr was
applied. Sub-morphologic cells were defined based on knowledge of site processes,
engineering activities, and erosion/accretion trends indicated by the shoreline position data.
The sediment budget based on sub-morphologic cells is presented in Fig. 5. Net LST rates
for the regional sediment budget are compared to the potential LST calculations in Fig. 6.
Figs. 5 and 6 and Table 1 indicate that nearly all net LST values of the regional sediment
budget are lower than those estimated by earlier studies, and lower than the potential LST
calculations along the Westhampton Reach. All of the previous sediment budget
formulations have used estimates of net LST at Fire Island Inlet to either determine (RPI
1983) or provide a checkpoint (Kana 1995, and this study) for the budget. It is believed that
estimates of net LST based on impoundment may be too high to characterize existing
conditions, due to other contributing processes (e.g., ebb shoal welding) and change in the
impounded shoreline position to one more parallel with incoming waves. Estimates of net
LST at Fire Island Inlet based on dredging must consider the gross transport components
of sand entering the inlet both from Fire Island and Gilgo Beaches.
This study used estimates of net LST based on an analysis of Democrat Point spit
growth, which resulted in lower net LST rates at Fire Island than previously reported.
The differences between potential LST calculations and the regional sediment budget,
especially apparent in the Westhampton Reach (see Fig. 6), indicate that the littoral
system may have had a deficit of material for this barrier during the 1979 to 1995 period.
Rosati et al.
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