UNIFORM 1 



FLUX 



Vidi = V2d2 



N,;^;^:.:^ 



^v- 



;\.;kNL^:,^\ 



SHORELINE: NO FLOW (WALL) 

 AT SWL 



\ \\\\\\\\ 



-3 



UNIFORM 



FLUX 



Vgda = V4d4 



^OFFSHORE: RADIATION CONDITION 



§ + c-f-=0 

 9t 9x 



Figure 9. Boundary conditions used in numerical model CURRENT 



Transport inside the surf zone 



59. Inside the surf zone it is the wave breaking process that is 

 primarily responsible for the transport of sediment. This process is quite 

 complex and not well understood. There is even considerable disagreement on 

 the primary mode (bed load or suspended load) of sediment transport in the 

 surf zone (Komar 1978). Thus a model that determines transport in the surf 

 zone must be empirical, to some degree, in its formulation. 



60. The surf zone transport model used in this study is based upon an 

 energetics concept developed by Bagnold (1963) who reasoned that the wave 

 orbital motion provides a stress that moves sediment back and forth in an 

 amount proportional to the local rate of energy dissipation. Although there 

 is no net transport as a result of this motion, the sediment is in a dispersed 

 and suspended state so that a steady current of arbitrary strength will trans- 

 port the sediment. Thus breaking waves provide the power to support sand in a 

 dispersed state (bed and suspended load) , while a superimposed current (litto- 

 ral, rip, tidal) produces net sand transport. 



61. The total littoral transport rate 1^ (vertically integrated and 

 parallel to the shoreline) within the surf zone can be related to the wave 

 conditions at the breaker line by 



36 



