of deepwater wave heights based on wind-casting techniques, showed that 

 almost three quarters of all deepwater waves approached Long Island from 

 the directions east-northeast through south-southeast. The largest deep- 

 water waves computed from the wind data were from 25 to 30 feet (7.6 to 

 9.2 meters) in height. These wave heights would be considerably reduced 

 as water depths decreased toward shore; however, the wave period and 

 direction would generally remain the same. It is the constant impinge- 

 ment of waves from the southeast which results in the observed net west- 

 ward longshore drift of beach sand. Longshore sand transport results 

 when ocean waves intersect the coast at oblique angles. The drift direc- 

 tion and volume of detritus moved vary greatly depending on seasonal 

 weather conditions; the net longshore drift for the south shore of Long 

 Island is predominantly from east to west. The net volume of sand moved 

 is estimated from 300,000 to 600,000 cubic yards (229 to 458 X 10^ cubic 

 meters) per year (Taney, 1961; Panuzio, 1968; U.S. Army, Corps of Engi- 

 neers, 1971). Net littoral drift for eastern Long Island (Shinnecock 

 region) is 300,000 cubic yards (229,000 cubic meters) per year, increases 

 to about 600,000 cubic yards (458,000 cubic meters) at Fire Island, and 

 then drops to 400,000 cubic yards (306,000 cubic meters) per year at 

 Rockaway Inlet on western Long Island (Panuzio, 1968). 



II. SHELF GEOMORPHOLOGY, SHALLOW STRUCTURE, AND STRATIGRAPHY 



1. Continental Shelf Morphology . 



The New York Bight Continental Shelf (Fig. 1) has probably received 

 more scientific study over a longer period than any other sea floor area. 

 Dana (1890) was one of the first to explore the Atlantic shelf in 1863, 

 documenting the existence of both the Hudson and Block (submarine) 

 Channels on the shelf by fairly detailed bathyraetric surveys. Based 

 on these surveys, Dana suggested that these channels originated during 

 periods of global glaciation when sea level was depressed several hundred 

 feet and the Hudson and Connecticut Rivers flowed in these channels across 

 the exposed shelf to the canyons at the shelf edge. A complete discussion 

 of the history of research on the Atlantic shelf channels and canyons is 

 provided by Shepard and Dill (1966), Research by Lindenkohl (1885), 

 Gulliver (1899), Alexander (1934), Johnson (1939), Veatch and Smith (1939), 

 Garrison and McMaster (1966), Knott and Hoskins (1968), McKinney and 

 Friedman (1970), Uchupi (1970), Garrison (1970), and McMaster and Asraf 

 (1973) has added significantly to knowledge of the Atlantic shelf morph- 

 ology, substructure, and geologic history. However, there are still many 

 sea floor features of unknown origin and many features whose origins may 

 be explained by conflicting hypotheses. 



The Continental Shelf south of Long Island (Fig, 5) is a gently 

 seaward-sloping plain, about 80 miles (129 kilometers) wide from the coast 

 seaward to the shelf edge (Fig. 1) . This shelf is a discrete compartment 

 bound on the west by the deeply incised Hudson (shelf) Channel (Fig. 5) 

 and bound on the east by the broader, but equally prominent Block (shelf) 

 Channel (Fig. 1) . There are several other linear depressions on the shelf 

 which also appear to be ancestral drainage channels but these are of 



24 



