r ? (2) l- 



^ — "NO EROSION" 







^"POSSIBLE EROSION" 







- n 



CERTAIN EROSION" 













- T'l 









■(2) 



* -: 



■ 

 ■ 







1 1 



• 



LEGEND 





- M 



-fl 



1 1 1 



■ 

 i i i 



• L 9 /x 

 ■ L,Al 

 /,n NUMBER OF 

 w DATA POINTS 



1 1 1 





3 4 5 6 



L g /X , Lg /X ; 



Figure 26. Evaluation of Seiji, Uda, and Tanaka's (1987) limits for gap 

 erosion (from Rosati (1990)) 



where d m is the annual seaward limit of the littoral zone, H e is the deepwater 

 wave height exceeded 12 hr per year, S is the ratio of sediment to fluid 

 density, g is the acceleration of gravity, and T e is the wave period 

 corresponding to the wave height. 



For headland structures (tombolo formation), structures should be sited at 

 an approximate depth of 



d = — headland structures 

 3 



(10) 



This relationship was evaluated using the recommended depth for salient 

 formation at all sites except Colonial Beach, where the recommended depth 

 for tombolo formation was used. A good correlation between depth at the 

 structure and Hallermeier's recommended depth exists for all but the 

 Lakeshore Park data (Figure 27). 



Japanese Ministry of Construction (JMC) method. The JMC method is 

 a step-by-step iterative procedure with specific guidelines to follow during the 

 breakwater design process (Japanese Ministry of Construction 1986; Rosati 

 1990; Rosati and Truitt 1990; EM 1 1 10-2-1617). The procedure used for 

 design is advantageous over the limited design guidance available in the 

 United States; however, the method has several disadvantages for design of 



44 



Chapter 2 Functional Design Guidance 



