Alternative 5: Mechanical Fillet Mining 



This alternative involves using a mechanical scraper/dragline or bucket system to physically 

 move material from the offshore and nearshore areas of the updrift fillet to a holding basin near 

 the back beach. From this holding basin, the material would be fluidized and pumped downdrift 

 similarly to the previously discussed alternatives involving hydraulic pumping. For practical 

 purposes, this alternative is the same as the semifixed alternative discussed previously with a 

 different sand removal technique attached. Once the material is scraped to the holding basin, a 

 jetpump/submerged pump system is required to fluidize the sand and, using booster pumps, 

 pump it to the discharge site. 



Draglines or scraper systems have been used in beach mining operations on less exposed 

 coasts in the past (Renfroe 1971, Dalrymple 1970, Gee 1965). They consist of a land-based 

 facility containing the drive motors and controls for the cabled bucket scraper. These cables are 

 attached to an anchored, floating barge offshore which serves as the seaward limit of operation of 

 the scraper system. In some instances, this offshore barge can be moored to allow movement 

 up/downcoast for increased mining capacity (Figure 29). 



The lack of installation experience in coastal regimes in recent years limits the confidence in 

 the ability and practicality of implementation for bypassing using a mechanical system. In 

 addition, there are several factors that may restrict or prohibit this type of system: 



a. Suspension of sand causing undesirable plumes and increasing losses from the borrow 

 area (Dalrymple 1970). 



b. Anchoring a barge system connected by cables in an open ocean environment. 



c. Corrosion of moving parts (gears, cables, and cable drums, etc.). 



d. Aesthetics. 



e. Cost unknowns (initial, operational, and replacement). 



Because of the lack of recent experience, costs can only be loosely estimated. Gee (1965) 

 provides an equipment cost in 1963 dollars of $40,000 for a system similar to that shown in 

 Figure 29 for Jupiter Island, Florida. The unit cost to place 500,000 yd 3 of material on the beach 

 was $0.24/yd 3 . Accounting for a 343-percent increase from FY68 to FY97 (HQUSACE (1996) 

 only goes back to FY68) and a 16-percent locality increase from Florida to New York , these 

 costs would be $159,000 ($0.95/yd 3 ) in 1997 dollars. Note these costs are only for the dragline/ 

 scraper portion of the system. Total costs will include the cost of fluidizing and pumping the 

 material from the holding basin to the discharge point. Because this system is similar to the 

 semifixed alternative, construction, operation and replacement costs will be similar as presented 

 in Tables 15 to 17, less the crawler crane associated costs. Additionally, pipeline costs may also 

 be reduced because the fluidization system will be immediately adjacent to the holding basin; 



68 Chapter 5 Other Bypassing Studies 



