States is the 13.7-kilometer-long (8.5-mile) Los Angeles-Long Beach breakwater 

 complex built between 1899 and 1949. Other U.S. offshore breakwaters are 

 listed in Table 5-3 of Chapter 5. 



2. Segmented Offshore Breakwaters . 



Depending on the desired function of an offshore breakwater, it is often 

 advantageous to design the structure as a series of short, segmented break- 

 waters rather than as a singular, continuous breakwater. Segmented offshore 

 breakwaters can be used to protect a longer section of shoreline, while allow- 

 ing wave energy to be transmitted through the breakwater gaps. This permits 

 a constant proportion of wave energy to enter the protected region to retard 

 tombolo formation, to aid in continued longshore sediment transport at a 

 desired rate, and to assist in maintaining the environmental quality of the 

 sheltered water. Additionally, the segmented breakwaters can be built at a 

 reasonable and economical water depth while providing storm protection for the 

 shoreline. 



Figure 6-66 illustrates the structural details of the segmented rubble- 

 mound breakwater at Lakeview Park, Lorain, Ohio, which is on Lake Erie. This 

 project, which was completed in October 1977, consists of three detached 

 rubble-mound breakwaters, each 76 meters long and located in a water depth of 

 -2.5 meters (-8 feet) low water datum (LWD). The breakwaters are spaced 50 

 meters (160 feet) apart and are placed about 145 meters (475 feet) offshore. 

 They protect 460 meters of shoreline. The longer groin located there was 

 extended to 106 meters (350 feet), and an initial beach fill of 84,100 cubic 

 meters (110,000 cubic yards) was placed. A primary consideration in the 

 design was to avoid the formation of tombolos that would interrupt the 

 longshore sediment transport and ultimately starve the adjacent beaches. 



Immediately after construction, the project was monitored for 2 years. 

 Findings indicated that the eastern and central breakwaters had trapped 

 littoral material, while the western breakwater had lost material (Walker, 

 Clark, and Pope, 1980). The net project gain was 3800 cubic meters (5,000 

 cubic yards) of material. Despite exposure to several severe storms from the 

 west during periods of high lake levels, there had been no damage to the 

 breakwaters or groins and no significant erosion had occurred on the lake 

 bottom between the breakwaters. 



X. CONSTRUCTION MATERIALS AND DESIGN PRACTICES 



The selection of materials in the structural design of shore protective 

 works depends on the economics and the environmental conditions of the shore 

 area. The criteria that should be applied to commonly used materials are 

 discussed below. 



1 . Concrete . 



The proper quality concrete is required for satisfactory performance and 

 durability in a marine environment (see Mather, 1957) and is obtainable with 

 good concrete design and construction practices. The concrete should have low 

 permeability, provided by the water-cement ratio recommended for the exposure 

 conditions; adequate strength; air entrainment, which is a necessity in a 



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