transport of sediment was dominant or equal to that generated by incident 

 waves in all cases and at all times. 



Pilkey and Field (1972) and Wright et al. (1991) distinguish between 

 the primary causes of onshore and offshore cross-shelf sediment transport. 

 Pilkey and Field (1972) summarize the mechanisms of onshore transport 

 of sediment on the irmer shelf, which include wave and tidal current phe- 

 nomena such as: 



a. Onshore component of asymmetrical wave orbitals under shoaling 

 conditions. 



b. Onshore-oriented dominating tidal flood currents in shallow water. 



c. Both the onshore and offshore components associated with 

 storm-induced bottom currents. 



In addition, Wright et al. (1991) state that incident waves are an important 

 mechanism of the onshore transport of sediment. 



Sediment transport mechanisms documented to cause onshore and off- 

 shore cross-shore sediment transport include the following: 



a. Orbital asymmetry . 



b. Interaction of incident waves with infragravity waves and mean 

 offshore flows. 



c. Wave groupiness. 



d. Slope of the shelf and effects of gravity. 



e. Rip currents (Wright et al. 1991). 



Discussion of these mechanisms of inner shelf offshore and onshore cross- 

 shore transport follow. 



Orbital asymmetry. Findings by Cook and Gorsline (1972) during 

 studies at Palos Verde, California, as supported by May (1979) and Wright 

 et al. (1991) indicate that orbital asymmetry-created currents during wave 

 shoaling transpon sediment in both the onshore and offshore directions. 

 These findings include the following: 



a. Both onshore and offshore asymmetry of currents were documented 

 during wave shoaling. Long-period swells and offshore breezes 

 cause a net onshore transport of sediment, while short-period waves 

 and onshore winds are associated with neutral or offshore flow. 



26 



Chapter 3 Evidence of Cross-Shore Sediment Transport 



