separate transmission coefficient. Detached breakwaters with variable wave 

 transmission alongshore (due, for example, to structure deterioration and 

 settling) can be modeled by several smaller contiguous sections having dif- 

 ferent transmission coefficients. Gaps between breakwaters as well as 

 detached breakwaters which allow wave transmission (K T > 0) are called "energy 

 windows" as they represent areas in the offshore through which wave energy can 

 directly penetrate. 

 Treatment of Transmission and Diffraction 



Wave transmission is assumed to possess the following properties, which 

 will be used to examine model predictions in the examples below: 



a. As the transmission coefficient approaches zero, calculated wave 

 diffraction should equal that given by standard diffraction theory for 

 an impermeable infinitely high breakwater. 



b. If two adjacent energy windows have the same transmission coefficient, 

 (for example, two detached breakwaters with the same K T or one 

 breakwater with K T = 1 situated next to a gap) , no diffraction should 

 occur . 



c. On the boundary between two energy windows with different transmission 

 coefficients, wave energy should be conveyed from the window with 

 higher waves to the window with smaller waves. The amount of wave 

 energy transferred should be proportional to the ratio between the two 

 transmission coefficients. 



Fig. 3 shows the calculated distribution of breaking wave height behind a 

 semi -infinite detached breakwater as a function of transmission. The break- 

 water is located 250 m from the shoreline. The wave period is T = 6 sec, and 

 the incident wave crests are parallel to the straight shoreline. The breaking 

 wave height H alongshore is normalized by the wave height at the tip of the 

 breakwater, H tp . The curves labeled by a denote breaking waves incident 

 from the lateral side of the structure, and b denotes waves transmitted 

 through the structure. The total wave height is obtained as the sum of these 

 two wave systems, denoted by c. (Calculated breaking wave angles and long- 

 shore sand transport rates are discussed in Hanson and Kraus , in prep.) 



For K T = 0.0, only diffraction occurs, and no waves pass through or over 

 the structure. The curves a and C are therefore identical. 



45 



