The larger regional problem of reestablishing an uninterrupted sediment supply to the 

 downdrift beaches near Tiana Beach (i.e., beyond the ebb shoal reattachment) is the objective of 

 this effort. The problem is best addressed by a bypassing/sand management plan. 



Bypassing Concepts and Methods 



Sand bypassing can be described by the mode of operation and operation schedule. The 

 mode of operation deals with the fundamental way in which the sediment is collected. In an 

 interception mode, bypassing is performed from a location that has a readily available source of 

 material and minimal storage volume. It only functions when sediment is moving to it and thus 

 is best used when drift volumes and transport paths can be predicted with reasonable accuracy 

 and the range of transport rates is not broad. An interception-mode system generally only 

 captures a portion of the littoral drift, and it may be impractical to design for maximum transport 

 rates associated with extreme events. Therefore, some material may be missed for bypassing 

 because of the lack of storage. The alternative to an interception-mode system is one that has a 

 storage area. Storage areas may be either natural or man-made such as accretion fillets, bars, 

 deposition basins, or channels. Storage areas allow flexibility in dealing with high transport rates 

 by trapping material that can be bypassed during times of below-normal transport. This mode 

 allows for more scheduled operations and may be able to use a lower capacity system on a more 

 continuous basis (HQUSACE 1991). 



Operation schedule can be either continuous or periodic. A continuous system runs on a 

 regular basis that may coincide with some convenient working period (regular working hours, 

 daylight, etc.). Continuous operation may be used for both interception and storage modes, 

 though during periods of high transport rates, a continuous system in interception mode may be 

 overwhelmed. The best application for continuous operation is in the storage mode. In this 

 mode, the system operating schedule is less affected by short-term transport rate variations 

 because of the flexibility provided by the storage area. A system operating periodically only 

 bypasses sand when necessary— whether by availability of sand or due to social, recreational, or 

 environmental factors. For example, an inlet where periodic maintenance dredging removes 

 material from the channel and places it on downdrift beaches is a periodic bypass system 

 operating in storage mode. It operates periodically when the storage area, the navigation 

 channel, is "full" (HQUSACE 1991). 



From a conceptual view, the most desirable bypass system for Shinnecock Inlet is one that 

 operates either continuously or periodically in a storage mode. Much of the littoral transport 

 material at Shinnecock is trapped or stored in the large updrift fillet and ebb shoal, thereby 

 providing ideal sources of material for bypassing. Continuous (or semi-continuous) or periodic 

 scheduling is a factor of the system selected, which depends on both cost and how the material 

 must be delivered to the downdrift beach. If a more or less continuous delivery schedule 

 throughout the year is desired, then some type of fixed plant operating from the updrift fillet 

 would be selected. If a continuous delivery is not necessarily required, costs and sand sources 

 may allow for a floating plant operating periodically from either the channel, ebb, or flood shoal 



38 Chapter 4 Design Criteria 



