One unusual morphologic feature evident in the 1994 data is a deep pit - almost a channel - 

 about 300 m west of the west jetty trending approximately in a north-south direction. The deep 

 part of the pit, -6.1 m mllw, extended to within 150 m of the shore. The pit is immediately 

 offshore of the portion of the beach experiencing the greatest erosion. 



1996 Morphology 



The SHOALS helicopter system was mobilized to survey Shinnecock Inlet again in May and 

 June 1996. This survey covered the ebb shoal more completely than the 1994 survey, as shown 

 in Figures 11 and 12. 



The shoal was shaped in the form of two irregular lobes that flanked the mouth of the inlet. 

 The east lobe was narrow and projected seaward parallel to the east jetty. The west lobe was 

 approximately triangular-shaped, with the seaward edge dropping off to the south. The bar front 

 on this west lobe was marked by closely spaced contours that extended from about -3.0 to -6.7 m 

 mllw. The west end of the lobe approached the shore about 1,800 m west of the west jetty. 



A north-south channel ran from the mouth of the inlet seaward between the two lobes. This 

 is the area that was dredged as a deposition basin in 1993, which in 1996 was still deeper than the 

 surrounding ebb shoal lobes. Seaward (south) of the channel, the shoal dropped off into deep 

 water, with the bar front extending from -9.1 to -12.2 m mllw. The distance from the end of the 

 jetties to the seaward edge of the shoal was about 1,100 m. 



The deep pit adjacent to the west jetty, described in 1994, was still present. Depths greater 

 than -5.5 m mllw are found within 150 m of shore. Some physical process appears to be causing 

 erosion and sediment transport in this area. Possibly, waves are refracted at the edge of the shoal 

 and concentrate their energy in this area. Other possibilities include sand depositions in the reach 

 immediately downdrift from the jetties and erosion by a tidal eddy in that area. The pit extends 

 perpendicular to the shore and does not resemble marginal flood channels found at many other 

 inlets (these are typically parallel to the shore and channel the flood tide into the inlet mouth). 

 Without current or drifter data in this area, these hypotheses cannot be tested. Nevertheless, it is 

 likely that the linear pit and the processes which are maintaining this deep area are related to the 

 serious erosion experienced along the adjacent shore. 



Erosion west of the inlet 



The shore west of the west jetty has been eroding since the jetties were completed in 1953. 

 Between 1954 and 1974, while the updrift fillet was filling with sand, the beach fronting Dune 

 Road receded from about 213 m seaward of the road to 137 m (USAE District, New York 1988). 

 Once the fillet east of the east jetty was largely filled around 1974, additional littoral material 

 bypassing the inlet temporarily stabilized the zone west of the inlet. But by 1978, erosion began 

 to increase again, and by March 1983, there remained only 91 m of beach fronting Dune Road. 



1 4 Chapter 2 Geologic Setting and Morphologic Development 



