computations performed on the shore processes grid. Figures 22 and 23 show 

 typical tidal computations performed on the nearshore processes grid. The 

 figures show mean ebb tidal currents for existing conditions and for two 

 jetties with a 2,500-ft spacing. Only flows in the vicinity of the inlet are 

 shown. Part of the ebb-tidal delta shoal was exposed at this time in the 

 tidal cycle. 



56. The numerical tide and surge model for Oregon Inlet (Leenknecht, 

 Earickson, and Butler 1984) was used to simulate also storm surge elevations 

 and currents for two storms of record, namely, Hurricane Donna (1960) and the 

 1962 Ash Wednesday storm. Results obtained for the 1962 Ash Wednesday storm 

 were used in this study, as discussed in a later section. 



Sediment Transport Models 



Transport inside the surf zone 



57. Inside the surf zone it is the wave breaking process that is pri- 

 marily 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. 



58. The surf zone transport model developed 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 

 (littoral, rip, tidal) produces net sand transport. 



59. Komar (1974) has given the following theoretical velocity distribu- 

 tion for a longshore current across the surf zone on a plane beach: 



V = AX + B X P 1 for < X < 1 (69) 



45 



