Appendix D 



Simulation of 1949 Barrier Topography 



Once Shinnecock Inlet was cut by the 1938 hurricane, the flood shoal grew rapidly. 

 Volumetric computations (discussed in the main body of the report) show that between 1933 and 

 1949, about 2,200,000 m 3 of sand accumulated on the flood shoal. Some of this sand came from 

 the barrier where the inlet was incised, while the rest came from interrupted littoral drift swept 

 into the inlet on the flood tide (there is no significant amount of riverine sand brought into 

 Shinnecock Bay). To determine sediment transport along the south shore, it was necessary to 

 evaluate the relative proportion of barrier-derived sand versus littoral transport-derived sand. 



Topographic information about the Long Island south shore in the Shinnecock area before the 

 1938 hurricane indicates that the barrier was continuous and consisted of dunes and marshy 

 regions. Unfortunately, actual elevations are not shown on the early topographic sheets. The 

 hurricane of 1938 is said to have "devastated the dunes," and post-storm aerial photographs show 

 vast overwash areas, but these images provide little useful data regarding the prestorm 

 morphology. Therefore, to determine a volume of sand eroded from the barrier, the pre- 1938 

 topography was simulated. 



To create a simulated barrier profile, the topography was measured across the contemporary 

 barrier near Shinnecock Inlet along nine lines (Figure Dl). These extended from the south shore 

 waterline at an azimuth of 339 deg across the barrier to the north shore. The cross-barrier lines 

 were spaced along the coast at the same positions as the beach and offshore profiles used for the 

 Atlantic Coast of New York monitoring program. Topography was measured off detailed charts 

 developed from 1995 aerial photographs (prepared for U.S. Army Engineer District, New York, 

 by Erdman Anthony Engineers). The nine profiles were averaged in a computer spreadsheet 

 program, and the average profile was used to simulate the pre-hurricane topography (Figure F2). 

 The nine profiles included dunes with crest elevations ranging from 4 to 8 m and flat marshy 

 zones. 



Appendix D Simulation of 1949 Barrier Topography D1 



