as a part of this study indicated a net LST rate 3 km east of Shinnecock Inlet equal to
115,000 m3/yr. Applying this rate, several modifications to the conceptual budget could be
postulated such that Eq. (1) is balanced:
1. Replace offshore losses due to sea level rise with an onshore source equal to 76,000
+ 33,000 m3/yr;
2. Increase beach fill placement from zero to 170,000 + 33,000 m3/yr;
3. Increase the mean bluff contribution from 33,000 m3/yr to 203,000 m3/yr;
4. Increase the volumetric loss of the barrier from 6,000 to 176,000 + 33,000 m3/yr
(equal to 143,000 to 209,000 m3/yr), which is equivalent to a shoreline change rate
for the entire barrier of approximately 0.3 m/yr; or
5. A combination of modifications (1) through (4).
Modification (1) proposed above does not have any data for support, and therefore is
omitted as a consideration. For modification (2), a review of the analyses conducted within
this study indicates that beach fill placement from 1933 to 1979 was approximately 39,000 m3/yr,
indicating that an assumption of no beach fill placement from 1979 to 1995, despite a lack
of data, might be unreasonable. Increasing the placement rate to the required 170,000 m3/yr
(modification (2)) does not seem realistic. However, it is believed that undocumented beach
fill placement has occurred for the Montauk Reach during the 1979 to 1995 period.
Modification (3) is a potential consideration, although data and previous sediment budgets
do not support this large bluff contribution rate. Modification (4) appears more reasonable.
Considering the shoreline change rates for this barrier, three of the six time periods
evaluated within this study meet or exceed the required erosion rate of 0.3 m/yr, indicating
that this is not an unreasonable change to the conceptual sediment budget. If the net LST
rate just east of Shinnecock Inlet were required to be equal to that of previous studies
(219,000 to 233,000 m3/yr), the required shoreline change rate for the Montauk Reach
would be 0.48 to -0.51 m/yr. Again, three of the six time periods meet or exceed this
required erosion rate. Based on this analysis, the regional sediment budget has been
formulated to employ modifications (2) and (4) such that the net LST rate approximately
3 km east of Shinnecock Inlet agrees with the potential LST calculations at this location,
115,000 m3/yr. Thus, the volumetric change rate, accounting for any beach fill placement,
is assumed to range from 143,000 to 209,000 m3/yr (Fig. 4). This assumption will be
checked with accepted values of net LST rates at the other inlets, and modified if necessary.
Shinnecock Inlet. The values shown in Fig. 4 applied in Eq. (1) require a net transport
3 km west of the inlet equal to 45,000 m3/yr. From inspection of aerial photographs and
visual observations at the site, this result is reasonable.
Westhampton Reach. Application of Eq. (1) results in a net LST rate 3 km east of
Moriches Inlet equal to 117,000 m3/yr. The previous sediment budgets estimated a range
from 45,000 to 140,000 m3/yr, lower than Taney' original estimate (230,000 m3/yr).
s
However, all the sediment budgets reflect conditions after construction of the Westhampton
Groin field (completed in 1970), which interrupted the net LST. The conceptual budget is
considered reasonable.
Moriches Inlet. Application of Eq. (1) indicates a net LST equal to 140,000 m3/yr 3-km
west of the inlet, directed to the west. Previous sediment budgets have estimates ranging
Rosati et al.
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