Semifixed (semi-mobile) systems 



A semifixed plant is one that is generally fixed to a project site but not to a specific area 

 within the site. The mobility afforded by a semifixed plant increases the effective storage area 

 available to be mined. An example of this is the Indian River Inlet, Delaware Bypass System 

 (Figure 21). This plant is fixed in that the dredge pumps are immovable on the backbeach, but 

 the jet pumps are deployed from a crane that can mine sand from the entire jetty fillet, thus 

 maximizing the storage area. During storms, the crane can move near the pump house on the 

 backbeach to reduce potential storm damage. 



A list of equipment that can be or has been used in fixed, mobile, and semifixed bypass 

 systems is shown in Table 10 (HQUSACE 1991). This list is not exhaustive and could be 

 expanded based on particular needs or sites. 



Table 10 



Equipment That Can Be Used for Bypassing 



Floating Dredges 



Land-based 



Hydraulic Equipment 



Trailing suction hopper 



Dragline 



Dredge pump 



Cutter-head 



Clamshell 



Jet pump 



Plain suction 



Backhoe 



Other solids-handling pumps 



Bucket ladder 



Bulldozer 





Clamshell 



Dump truck 





Dipper 







Backhoe 







Design Considerations 



Quantity 



In spring/summer 1996, the Baltimore office of MNE, under contract to NAN, conducted a 

 detailed coastal processes study of Shinnecock Inlet and the adjacent shoreline. One aspect of 

 the study was to revisit and improve upon previous sediment budget estimates for this reach of 

 Long Island. USAE District, New York (1988) summarized the sediment budget at Shinnecock 

 Inlet as having an approximate yearly net transport of 229,000 m 3 (300,000 yd 3 ) toward the west 

 with about 76,500 m 3 /year (100,000 ydVyear) being deposited on the ebb shoal. The NAN and 

 MNE considered those values preliminary because of limited data on ebb shoal growth, and 

 MNE sought to improve the confidence in longshore transport rates by performing analysis with 



Chapter 4 Design Criteria 



41 



