Coastal Evolution in Connection with Inlet Openings
The second simulation involved the period 1931-1983 during which Shinnecock and
Moriches Inlets were created. Furthermore, the inlets went through large changes in cross-
sectional areas, and Moriches Inlet closed temporarily in 1951 before it was artificially
opened again. Fig. 5 illustrates how the minimum cross-sectional area varied for the two
inlets during the simulation period. The figure is based on historic data (Czerniak 1977;
Morang 1999), linearly interpolated to supply time-varying input values. Equilibrium
shoal volumes were derived from the cross-sectional areas (Walton and Adams 1976). It
was assumed that the shoal and bars at the inlets would drive towards equilibrium volumes
defined based on the instantaneous cross-sectional areas. The same wave time series
served as input as for the calculations of the annual net longshore sediment transport rate
previously described. The three WIS Stations provided wave information, and the time
series derived for 1976-1995 was applied repetitively.
Fig. 6a plots measured and predicted shoreline positions in 1983 as well as the initial
shoreline. The shoreline measured in 1870 was taken as the initial shoreline, because no
measurements were available closer in time to 1931. The calculations yielded the correct
magnitude of advance updrift and recession downdrift of the inlets, as well as the regional
trend of shoreline evolution. Directly downdrift of the inlets, the predicted shoreline shape
deviates somewhat from the measurements, attributed to incomplete representation of the
influence of the attachment bar and tidal-induced transport near the inlet. Fig. 6b displays
an enlargement of the shorelines given in Fig. 6a in the vicinity of the inlets.
2000
Moriches Inlet
Shinnecock Inlet
1600
1200
800
400
0
1930
1940
1950
1960
1970
1980
1990
2000
Time (year)
Fig. 5. Time evolution of minimum inlet cross-sectional area for Moriches and Shinnecock Inlets
based on Czerniak (1977) and Morang (1999).
Larson, Kraus, and Hanson
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