REEF BREAKWATER MODEL 



1.2 

 1.1 

 1 H 



.7 - 

 .6 - 

 .5 - 

 .4 



Related Parameters 



Dn50 = .420 m 

 Bn = 181.4 

 C = 2.0 



Input 



W50 = 



200 kg 



Pa = 



2700 kg/m 3 



P 



1025 kg/m 3 



he' = 



4 m 



h 



5 m 



At = 



32 m 2 



12 



15 



SPECTRAL STABILITY NUMBER Ns* 



Figure 52. Design graph of reef type breakwater using the spectral stability number N 

 (VanderMeer 1990) 



Performance Characteristics 



Low-crested rubble-mound breakwaters offer an attractive alternative to the 

 protection of shorelines against direct wave attack. It is important, both 

 functionally and structurally, to assess the effectiveness of a given breakwater 

 design by predicting the amount of wave energy transmitted, reflected, and 

 dissipated by the structure. Such performance characteristics involve a 

 number of complex processes. Some incident wave energy may be reflected 

 by the structure, some wave energy may be dissipated by turbulent interaction 

 with the armor layer, some wave energy may be dissipated internally within 

 the core of the permeable structure, and some may be transmitted through or 

 over the structure resulting in wave action in the lee of the structure. 

 Important factors identifiable in the process include incident wave conditions 

 and the structure's shape, material composition, and degree of emergence or 

 submergence. Figure 53 shows some of the key parameters involved in 

 determining a breakwater's performance characteristics. 



Chapter 4 Structural Design Guidance 



89 



