line is unity up to the calculation cell adjacent to the grid cell of the dif- 

 fracting tip. At that cell, the relative wave height is 0.5, dropping to 0.0 

 in the cell past the tip. Therefore, the total relative wave height is 1.0 

 along the entire shoreline. For clarity, the corresponding line C is not 

 shown in Fig. 3. 

 Influence of Kj 



Fig. 4 shows the case of a 200-m long detached breakwater located 250 m 

 offshore. Conditions are: H - 1.5 m, T ■= 6 sec, wave crests normal to the 

 initially straight shoreline, and simulation time of 180 hr. As expected, the 

 seaward extent of the salient decreases as wave transmission increases. Also, 

 the salient broadens slightly with increased transmission, and the eroded 

 areas on either side of the salient fill in. A simulation performed with K T = 

 1.0 produced no shoreline change and is not shown in Fig. 4. 

 Breakwater Segments with Different Transmission 



Fig. 5 shows a three -breakwater system with asymmetrical wave transmission 

 properties, the greatest transmission assigned to the right-hand breakwater 

 and least to the left-hand breakwater. The calculation is significantly more 

 complex than in the previous examples, because a point on the beach is open to 

 seven wave energy windows (four gaps and three transmitting breakwaters). The 

 curves in Fig. 5 display results for four cases with H = 1.5 m and T = 6 sec 

 distinguished by wave direction (0, +10, -10, and ±10 deg) ; the direction was 

 constant for 120 hr for the first three cases, and in the fourth case the 

 angle switched from +10 to -10 deg at the midpoint of the 120-hr simulation. 



The most obvious feature of Fig. 5 is the significant size difference of 

 the salients. The size and location of the largest salient is relatively 

 independent of wave direction, confirming conclusions of Hanson and Kraus 

 (1986a), who found that in diffraction-dominant situations, the response of 

 the shoreline behind breakwaters is most sensitive to incident wave height and 

 not wave direction (since almost identical semicircular diffraction wave 

 patterns are formed for any reasonable direction of the incident waves). In 

 contrast, the calculated shorelines in the lee of the middle and right break- 

 waters show substantial differences, similar to the open-coast situation in 

 which oblique wave incidence controls the direction of sand transport. 



47 



