Constraints 



Conditions specific to Shinnecock Inlet and the area may limit or prohibit the use of a 

 particular bypass system. In some cases, the preferred system design can work within these 

 constraints, or the constraint can be modified so as to minimize or eliminate problems. At 

 Shinnecock Inlet, one limitation that must be considered is the thickness of the sand layer. This 

 thickness is important for two reasons: determining the maximum depth of dredging or sediment 

 removal at the updrift fillet and in the ebb shoal (particularly important for the Punaise system); 

 and determining the conditions for tunneling under the inlet (or dredging a transverse channel 

 across the inlet) for laying a pipe. Five cores (one 12.2-m (40-ft) and four 6.1-m (20- ft)) were 

 taken at Shinnecock just offshore of the updrift fillet in November 1996. These cores were taken 

 in approximately 6-m water depths and showed an average sand layer thickness of about 6 m. 

 Below the 12.5-m depth (sand layer thickness of 6.5 m) the cores contained mud to the bottom of 

 the core (Alpine Ocean Seismic Survey, Inc. 1997). 



A second factor which constrains a fixed or semifixed alternative is the size of the ebb shoal. 

 As mentioned previously, the Shinnecock Inlet ebb shoal extends 2.4 km beyond the west jetty 

 (see Figure 14 for extent of ebb shoal). The desire to maintain the regional littoral transport will 

 require that any bypass material must be placed or pumped at least to this point to avoid the ebb 

 shoal shadow zone. This constraint may require the use of booster pumps with any alternative 

 having a pumping component (i.e., fixed/semifixed, CrawlcatlCrawldog, or Punaise). 



Equilibrium Ebb Shoal Volume 



Walton and Adams (1976) made a study of 44 inlets from the Pacific, Atlantic, and Gulf 

 coasts of the United States to evaluate the relationships between ebb shoal volume and tidal 

 prism. Their study divided the 44 inlets into three groups: highly exposed, moderately exposed, 

 and mildly exposed coasts. All of the highly exposed inlets were located on the Pacific, while 

 the moderately exposed inlets were primarily located on the Atlantic coast and the mildly 

 exposed inlets were on the Atlantic and Gulf coasts. They generally concluded that more sand is 

 stored in the ebb shoal at inlets on a low-energy coast than on a higher-energy coast. 



The relationships that Walton and Adams (1976) devised are based on the following equation 

 in English units: 



V = aP" (2) 



48 Chapter 4 Design Criteria 



