still retain most of their energy, and the wave period becomes longer. Two 

 sets of long-period waves approaching the coast with slightly differing 

 wavelengths may produce a resultant pattern, known as surf beat, that displays 

 a periodic variation in height. Waves change character as they enter progres- 

 sively shallower water, causing a variety of wave and breaker types, as well 

 as several distinctive zones of wave action (Figure 2). 



LITTDRAL ZONE 



- BACKSHDRE — 



BERMS ISUASH L 



n ZONE r 



'T^T^ 



-NEARSHDRE ZDNE- 



fDRESHDRE- 



ZONE r V" 



-DFFSHDRE ZQNE- 



-SHDREFACE — -| 



RIDGE 

 • RUNNEL" . .' 



Figure 2. Distinctive zones of wave action and morphologic characteristics of the littoral 

 zone 



Waves approaching a coast undergo a transformation of certain characteris- 

 tics which is called shoaling, because they have progressed into water depths 

 in which frictional interaction with the bottom affects their motion. Signifi- 

 cant transformation begins to occur when a wave enters water depths equal to 

 about one half the wave length. This transformation causes the wave speed 

 (celerity) to decrease, the wavelength to decrease, and the wave height to 

 increase, since more energy is packed into a smaller area. The wave front 

 may bend or change in direction as waves approach a shoreline and are 

 affected by bottom topography. This phenomena is known as wave refraction. 



Because of variations in bathymetry from place to place, the trans- 

 formation of a given deepwater wave is site-specific and must be calculated on 

 the basis of local bathymetric characteristics, bottom friction, and coastal con- 

 figuration. Wave refraction bends the wave front, so that it becomes more 

 nearly parallel with the bottom contours with decreasing water depths. For 

 this reason orthogonals generally converge on headlands and diverge in bays 

 (Figure 3). However, when waves cross irregular bathymetry, the waves may 

 be refracted upon themselves. 



Chapter 2 Relevant Processes and Factors 



11 



