Once the waves break, a surf zone is generated in which much smaller 

 waves are projected toward the foreshore and beach face. Upon breaking, the 

 motion of the water particles in a wave changes from orbital to linear. The 

 presence and the width of a surf zone are controlled by beach slope and tidal 

 phase (Ingle 1966). Beaches with gentle slopes, which are typically composed 

 of fine sand, are characterized by wide surf zones, whereas beaches with steep 

 slopes, which are composed of shingle and cobble, often lack surf zones. 

 Beaches of intermediate slope may have a surf zone at low tide, when wave 

 action is over flatter portions of the beach profile, but may lack a surf zone at 

 high tide when the waves break closer to shore over the steeper beach face. 



The landward component of this linear motion, which surges onshore 

 at a high velocity, is known as swash, while the lower-velocity return flow, 

 which is driven by gravity, is known as backwash. As waves approach the 

 beach at an angle, the oblique upward rush of swash, succeeded by the return 

 of backwash down the beach, results in a longshore movement of sediment. 



Deepwater wave characteristics can be estimated by an analysis of weather 

 map data over the period of interest, a process known as hindcasting (Coastal 

 Engineering Research Center (CERC) 1984). Waves may be observed from 

 shipboard or shore, or can be measured by gages deployed on buoys, struc- 

 tures, or on the sea bottom. Refraction analyses can be performed manually 

 by the orthogonal or wave-front method, or by computer methods when the 

 offshore relief, wave approach direction, and wave period are known. 



In addition to energy from incident waves, some energy may be transferred 

 to secondary wave motions called edge waves, which develop at right angles 

 to the shoreline. Edge waves have a maximum amplitude at the shoreline and 

 decline seaward. They develop differently on shorelines of differing 

 gradients. Many coastal forms and processes have been linked to edge wave 

 characteristics (Holman 1983; Carter 1988). 



The overall wave field at a site is typically formed by a combination of 

 waves from several different sources, some local and some distant. Longer 

 waves associated with storms reach deeper parts of the shoreface profile than 

 do shorter waves associated with calmer conditions. In order to be useful in 

 understanding the development and modification of coastal features and effects 

 on coastal engineering works, data collected by the methods described above 

 must cover a sufficient time span to record seasonal cyclic patterns and the 

 occurrence of intense storms. 



Tides 



Tides are characterized by a rhythmic rise and fall, or flood and ebb, of 

 sea level over a period of several hours. Because tides are generated by the 

 gravitational forces associated with the moon and the sun, changes in the 



14 



Chapter 2 Relevant Processes and Factors 



