in which 8 S = tan" 1 (3y/9x) is the angle of the shoreline with respect to the 

 x-axis. In GENESIS, an angle of deg signifies shore -normal wave incidence. 

 The angle 9 b drawn in Figure 10 is positive. 



ANGLE OF INCIDENT WAVE 

 CREST TO THE X-AXIS 



DISTANCE ALONGSHORE 



Figure 10. Definition of breaking wave angles 



138. If there are no structures to produce diffraction, the undif- 

 fracted wave characteristics are used as input to the sediment transport 

 relation (Equation 2). If such obstacles are present, breaking wave heights 

 and directions are recalculated, as described next. 



Breaking waves affected by structures 



139. Structures such as detached breakwaters, jetties, and groins that 

 extend well seaward of the surf zone intercept the incident waves prior to 

 breaking. Headlands and islands may also intercept waves. In the following 

 discussion, all such objects are referred to as structures. Each tip of a 

 structure will produce a near-circular wave pattern, and this distortion of 

 the wave field is a significant factor controlling the response of the 

 shoreline in the lee of the structure. Sand typically accumulates in the 

 diffraction shadow of a structure, being transported from one or both sides by 

 the oblique wave angles in the circular wave pattern and the decrease in wave 

 height alongshore with penetration into the shadow region. Accurate and 



66 



