14 



used while testing long-period wave conditions. Both the 0.0- and the 

 +7.0-ft swl's were used for testing short-period storm wave conditions. 



Factors influencing selection of test-wave characteristics 



In planning the testing program for a model investigation of harbor 

 wave-action problems, it is necessary to select dimensions and directions 

 for the test waves that will allow a realistic test of proposed improvement 

 plans and an accurate evaluation of the elements of the various proposals. 

 Surface-wind waves are generated primarily by the interactions between 

 tangential stresses of wind flowing over water, resonance between the 

 water surface and atmospheric turbulence, and interactions between indi- 

 vidual wave components. The height and period of the maximum wave 

 that can be generated by a given storm depend on the wind speed, the 

 length of time that wind of a given speed continues to blow, and the water 

 distance (fetch) over which the wind blows. Selection of test wave condi- 

 tions entails evaluation of such factors as: 



a. The fetch and decay distances (the latter being the distance over 

 which waves travel after leaving the generating area) for various 

 directions from which waves can attack the problem area. 



b. The frequency of occurrence and duration of storm winds from the 

 different directions. 



c. The alignment, size, and relative geographic position of the 

 navigation entrance to the harbor. 



d. The alignments, lengths, and locations of the various reflecting 

 surfaces inside the harbor. 



e. The refraction of waves caused by differences in depth in the area 

 seaward of the harbor, which may create either a concentration or a 

 diffusion of wave energy at the harbor site. 



Wave refraction 



When wind waves move into water of gradually decreasing depth, trans- 

 formations take place in all wave characteristics except wave period (to 

 the first order of approximation). The most important transformations 

 with respect to selection of test wave characteristics are the changes in 

 wave height and direction of travel due to the phenomenon referred to as 

 wave refraction. The change in wave height and direction is determined 

 by using the numerical Regional Coastal Processes Wave Transformation 

 Model (RCPWAVE) developed by Ebersole, Cialone, and Prater (1986). 

 This model predicts the transformation of monochromatic waves over com- 

 plex bathymetry and includes refractive and diffractive effects. The 

 model is very efficient for modeling large areas of coastline subjected to 



Chapter 3 Tests Conditions and Procedures 



