Wave refraction 



When waves move into water of gradually decreasing depth, transfonna- 

 tions take place in all wave characteristics except wave period (to the first 

 order of approximation). The most important transfomiations with respect to 

 the selection of test wave characteristics are the changes in wave height and 

 direction of travel due to the phenomenon referred to as wave refraction. 

 When the refraction coefficient K^. is determined, it is multiphed by the 

 shoaling coefficient K^, which gives a conversion factor of deepwater wave 

 heights to shallow-water values. The shoaling coefficient, a function of wave 

 length and water depth, can be obtained from the Shore Protection Manual 

 (1984). The change in wave height and direction may be detennined by using 

 a numerical combined refraction/diffraction (REFDIF) model. REFDIF was 

 selected to transform wave characteristics at the deepwater station to values at 

 the approximate location of the wave generator (shallow-water characteristics) 

 in the physical model. This model is suitable especially for varying bathyme- 

 try in domains which include islands and are surrounded by complex land 

 boundaries. Table 2 summarizes the refraction/diffraction analysis. The wave 

 height adjustment factor can be applied to any deepwater wave height to obtain 

 corresponding shallow-water values. Details of the REFDIF analysis are pre- 

 sented in Appendix A. Based on the refracted directions secured at the 

 approximate locations of the wave generator in the model, the following test 

 directions (deepwater direction and corresponding shallow-water direction) 

 were selected for use during model testing. 



Deepwater Direction 

 deg 



Selected Shallowz-Water Direction 

 deg 



Hindcast Waves 



45 



56 



67.5 



75 



90 



88 



103 



101 



Storm Waves 



80 



88 



78 



88 



Selection of test waves 



WIS hindcast data (Table 1) and stomi data were converted to shallow- 

 water values by application of the wave height adjustment factor (Table 2) and 

 are shown in Table 3. Characteristics of test waves selected for use in the 

 model investigation are shown in the following tabulation: 



Chapter 3 Test Conditions and Procedures 



17 



