a. For nonuniform protection over short distances use a single 

 detached breakwater. 



(1) Tombolo. The structure should be at least as long as the 

 shoreline to be protected and perhaps longer to ensure 

 enough shoreline advance along the entire project. The 

 breakwater should be placed offshore a distance between 

 two-thirds and one-half times its length. If the water 

 depth at this location is too great, move the structure 

 landward, keeping in mind the possibility of double tom- 

 bolo formation or of the structure ultimately acting as a 

 seawall. Otherwise, a different shoreline configuration 

 should be pursued. Design the breakwater to be imperme- 

 able and of sufficient crest elevation to minimize over- 

 topping during storm events. 



(2) Salient. As in the design for a tombolo, the structure 

 should be at least as long as the project. Make the dis- 

 tance offshore between one-and-one-half and two times the 

 length of the breakwater and design for low permeability 

 and infrequent overtopping. If the water depth at this 

 location is too great, move the structure landward and 

 increase wave transmission by increasing permeability 

 and/or overtopping. 



b. For nonuniform protection over longer distances use a segmented 

 breakwater. 



(1) Tombolo. The approximate size of the tombolo which will 

 provide the required average beach width will dictate the 

 distance offshore. The segment length should be roughly 

 one-and-one-half times this distance. Gap width will de- 

 pend on the design shoreline position opposite the gap. 

 If the region has a substantial longshore transport rate, 

 or beach fill is to be added, it may be possible to widen 

 the beach opposite the gap. Make the gap at least one 

 wavelength wide, but no greater than the segment length. 

 If the predominant wave direction is directly onshore, the 

 gaps will have to be very narrow for the opposite shore- 

 line to be advanced substantially. Use diffraction dia- 

 grams to determine the reduction in wave height opposite 

 each gap. Alter the gap size, keeping in mind the possi- 

 ble effects of a large water-level range and overtopping 

 driving currents through the gaps, or a small water-level 

 range causing stagnation in the embayment. If the water 

 depth at the structure is too great for feasible and eco- 

 nomical construction, the desired tombolo size, segment 

 length, distance offshore, and gap width may need to be 

 scaled down. Determine the number of segments (and gaps) 

 required to cover the length of the project. Slight ad- 

 justment of the segments and gap length or perhaps just 

 the end segments may be necessary to cover the required 

 length of shore. Design each segment to be impermeable 

 and overtopped infrequently. 



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