b. Zone II: From the break point to plunge point (breaker 



transition zone) . 



c. Zone III: From the plunge point to the point of wave reform- 



ation or to the swash zone (broken wave zone) . 



d. Zone IV: From the shoreward boundary of the surf zone to 



the shoreward limit of runup (swash zone). 



339. The division of the profile into different transport regions is 

 not immediately recognized viewing the net transport rate distributions (see, 

 for example, Figure 33) since the transport regions interact, and the long- 

 term average represented by the calculated distributions has a smoothing 

 effect. Nevertheless, from a physical point of view it is attractive and 

 productive to divide the beach profile into regions with different governing 

 transport relationships. In the following, net transport rate conditions are 

 investigated in the transport zones and in three zones related to wave and 

 sand characteristics. Empirically-based relationships for the net transport 

 rate are formulated for the different regions based on physical considerations 

 and observations from the data. 



Zone I : Net transport rate seaward of the break point 



340. The net cross -shore transport rate seaward of the break point has 

 probably been the most intensively studied of all regions on the profile, both 

 in the field and in the laboratory. Transport in the prebreaking zone is in 

 many cases governed by ripple dynamics (e.g., Inman 1957, Dingier and Inman 

 1977, Nielsen 1979, Sunamura 1981a). Sophisticated transport rate formulas 

 have been developed based on laboratory experiments (e.g., Madsen and Grant 

 1977, Sato and Horikawa 1987), but these empirically-based formulas must also 

 be supplemented by other information for their application. Such formulas 

 describe sand transport on spatial and temporal microscales which are not 

 compatible with the present approach of quantifying large-scale profile 

 features over intervals of tens of minutes. 



341. As a wave approaches the point of breaking, its velocity field 

 becomes more asymmetric with high, narrow peaks of onshore -directed flow and 

 broad troughs of flow directed offshore. This motion could cause material to 

 move either onshore or offshore depending on the elevation in the water column 

 at which a grain is suspended in relation to the duration of the on/offshore 



139 



