locations from baseline station 21.5 km through 22.5 km and from baseline station
24.0 km through 26.5 km. Erosion cusps can also be anticipated in two locations from
baseline station 23.0 km through 24.0 km and from baseline station 26.5 km through
27.5 km.
The 5-km-long shoreline coverage in Fig. 8 corresponds to the shoreline reach from Old
Inlet to Smith Point County Park (about 12 km west of Moriches Inlet). The segregation
between the locations where the accretion and erosion were found is reasonably apparent
in Fig. 8, suggesting again that the shoreline undulations tend to be positioned in the same
locations and do not propagate long distances as a collective unit. The interpretation of
Fig. 8 is that erosion cusps can be anticipated to occur between baseline stations 35.0 km
and 36.0 km and also between baseline stations 37.5 and 38.5 km. Accretion cusps can
be expected between baseline stations 36.0 and 37.5 km and also between baseline
stations 38.5 and 39.0 km.
Baseline locations or reaches where both the landward and seaward rms amplitudes are
exceeded indicate propagation of the shoreline undulations within a limited domain, for
example, in the vicinity of baseline stations 35.8 and 38.5 km in Fig. 8. Although this
analysis does not definitively answer the propagation question, it does provide some
insight into the spatial and temporal distribution of the shoreline undulations along the Fire
Island shoreline. In summary, the results shown if Figs. 7 and 8 are representative of
locations on Fire Island where shoreline undulations are frequently present and the trends
are readily apparent.
DESIGN CONSIDERATIONS
Based on the analysis presented above, the influence of shoreline undulations on a
typical beach erosion control design are discussed and potential design modifications are
suggested to improve the compatibility of the design with the presence of shoreline
undulations. Recent Federal beach fill projects in the northeastern U.S. have involved a
protective dune fronted by design berm widths in the 30-m range with an additional 15-m
wide advanced nourishment berm. The 15-m berm is constructed as a sacrificial feature
intended to ensure that the protective design berm width is preserved throughout the
renourishment interval (typically 3 to 6 years). The impact of the presence of shoreline
undulations on these typical design dimensions is illlustrated in Fig. 9. The shoreline
undulation signal developed from the April 1995 shoreline position data and plotted in Fig.
5 is superimposed on the post-construction shoreline in Fig. 9. As seen in the figure, the
development of shoreline undulations on the post-construction shoreline will effectively
reduce the sacrificial berm width that results from the placement of advanced nourishment
material over significant portions of the project. Based on the data plotted in Fig. 9, the
width of the advanced nourishment berm is less than half its intended width over 31
percent (3.1 km) of the project and the design berm is compromised over 13 percent (1.3
km) of the project. These conditions, which can be expected to occur either during
construction or soon thereafter, will undoubtedly lead to shorter than designed
renourishment intervals or a reduced level of protection because of encroachment into the
design berm. It is acknowledged that the shoreline undulations
Gravens
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