24 



sand grains are transported seaward in the form of a cloud by wave- 

 induced currents (Sunamura 1980). When P^ > P^, sand grains tend to roll 

 and jump as bed load and move shoreward. 



Inner Shelf Cross-Shore Sediment Transport 



Introduction 



Understanding of surf zone processes can be applied, at least in con- 

 cept, to processes occurring on the inner shelf. For instance, Wright et al. 

 (1991) applied surf zone sediment transport equations of Bailard (1981) 

 and Guza and Thornton (1985 a,b) to predict inner shelf cross-shore sedi- 

 ment transport. Wright et al. (1991) found poor agreement between these 

 surf zone and inner shelf sediment transport equations. Wright et al. 

 (1991) state that these types of equations are needed to better predict 

 cross-shore sediment transport on the inner shelf. 



For wind-driven current patterns, Vincent, Young, and Swift (1983) 

 divide the inner portion of the coastal ocean into the following three zones 

 based on controlling sediment transport mechanisms: 



a. Geostrophic (offshore; seaward of approximately the -15-m depth). 



b. Transition. 



c. Friction-dominated (seaward of the surf zone to approximately -10-m 

 depth). 



Landward of the 10-m contour in the friction-dominated zone, sediment 

 transport rates are on the order of 1 x 10 g/cm/sec and are primarily a 

 function of asymmetric wave orbitals while seaward of the 10-m contour 

 in the geostrophic zone, sediment transport rates are approximately 1 x 

 10 g/cm/sec (Vincent, Young, and Swift 1983). 



Geostrophic zone 



Geostrophic circulation of ocean waters and sediment transport in this 

 zone are controlled by the following factors: 



a. Cross-shore mean bottom currents resulting from wind shear and 

 tide-related currents. 



b. Currents generated by the Coriolis force. 



c. UpwelUng/downwelling conditions. 



Chapter 3 Evidence of Cross-Shore Sediment Transport 



