7 Conclusions 



Downdrift erosion caused by the inlet and structures at Shinnecock Inlet can be addressed by 

 mechanical bypassing. Several different bypass systems (five of which have been summarized 

 here) are technically capable of restoring the natural littoral transport. Bypassing to restore 

 natural longshore sediment transport has been successfully conducted at many inlets throughout 

 the United States and the world, so the problem at Shinnecock is not insurmountable. One 

 should consider, however, that restoration of longshore transport at Shinnecock Inlet may not 

 solve all the beach erosion problems experienced to the west. Although interruption of the 

 natural sediment transport is contributing to downdrift erosion, long-term barrier island retreat 

 caused by sea level rise has also contributed to historical erosion (0.3 -1.2 m retreat per year—see 

 Table 2). Mechanical bypassing can only mitigate those problems related to longshore sediment 

 transport interruption, but it cannot solve the more widespread erosion/retreat problem caused by 

 other mechanisms (i.e., sea level rise, lack of updrift sediment). Although artificial bypassing 

 can restore longshore sediment transport to natural levels, this restored sediment supply may only 

 solve the shore erosion problem where the material is placed and, with time, at adjacent reaches 

 downdrift. Bypassing is most effective when beach nourishment is first used to bring the beach 

 to its desired width; without the initial nourishment, bypassing can only maintain the existing 

 condition. 



Ideally, requirements for normal channel maintenance dredging should be reduced with any 

 of the bypass systems presented. The level to which any one alternative can reduce channel 

 shoaling cannot be determined from the information available for this study. Details on sediment 

 transport pathways are required to determine the source of the sediment that shoals in the 

 channel. Normal channel maintenance (if required) could continue as in the past with no impact 

 to any of the bypass systems. Following a beach/nearshore placement of channel maintenance 

 material, operation of the selected bypass system should be decided by the system operator with 

 input from the downdrift benefactors and considering the season and existing conditions. One 

 may argue that there should be no need to operate the fixed system for a time after channel 

 maintenance operations if the material is placed downdrift. However, depending on the time 

 frame of the maintenance dredging and the condition of the downdrift beaches, this may be 

 viewed as an extra source of material providing an extra benefit. Alternatively, placement of 

 maintenance material to supplement the bypassing system may allow a temporary shutdown of 

 the bypass system to allow for maintenance or repairs (though the non-pumping season is also 



Chapter 7 Conclusions 81 



