Protective Dune
0
Design Berm
30 m
20
Advanced Nourishment Berm
15 m
40
60
80
Shoreline Undulations (typical)
Ocean
100
20
22
24
26
28
30
Distance Along Baseline (km)
Fig. 9. Shoreline undulation impact on typical beach fill design.
plotted in Fig. 9 correspond to a specific shoreline reach at a specific historic point in time
and may not be representative of all locations at all times. However, the previous analyses
have quantified the landward rms amplitude of the shoreline undulations on Fire Island at
about 14 m (Table 3) which is very close to the typical 15-m advanced nourishment berm
width.
An improved design would involve reconsideration of the design goals and economic
justification (project benefits) for the overall project. In the case of Fire Island, major
project benefits result from the reduction of storm damages within the estuarine-margin
communities along the northern shoreline of Great South Bay. In fact, these "off-site"
benefits outweigh the benefits derived from the protection of properties on Fire Island.
The project will provide storm damage protection to the upland properties by preventing
breaching of the barrier island, which would lead to higher water levels in Great South
Bay and associated flooding of the low-lying communities that border the bay. Therefore,
a major design goal is to prevent breaching of Fire Island. Another design goal is to
reduce storm-induced damages to structures and properties on Fire Island. Both of these
design goals can be achieved through the construction of a dune and a wide protective
berm. However, as illustrated in Fig. 9, the occurrence of shoreline undulations will tend
to locally degrade the effectiveness of the typical design.
One approach to designing for the presence of shoreline undulation would be to
construct an even wider beach berm (a "shoreline undulation buffer" zone) upon which
shoreline undulations could form without compromising the design berm width or
significantly impacting the advanced nourishment berm. This approach however, would
Gravens
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