The Coriolis force is defined as an apparent force resulting in the path 

 deflection of an object due to the earth's rotation (Neshyba 1987). In the 

 Northern Hemisphere, an object or water body undergoing movement on 

 the earth's surface will be deflected to the right (clockwise) of the move- 

 ment. The Ekman transport or drift, a function of the Coriolis force, 

 states that as winds exert friction drag over an ocean of uniform density, a 

 thin layer of surface water moves at an angle from the original wind (to 

 the right in the Northern Hemisphere). This rotation continues as subsur- 

 face parcels of water are also rotated by the Ekman transport in that same 

 direction. Therefore, there is a depth at which the water moves opposite to 

 that of the surface wind (Neshyba 1987). Nummedal and Snedden (1987) 

 have documented the Ekman transport in a three-layer inner shelf flow 

 model, which shows that if surface currents are obliquely onshore, cur- 

 rents at mid-depths in the water column will be alongshore. Bottom cur- 

 rents will be oriented obliquely offshore. 



Upwelling and downwelling currents are also geostrophically control- 

 led currents that form due to orientation of the wind direction near a 

 coast. For instance, upwelling conditions occur when offshore-directed 

 winds transport surface waters in an offshore direction. Surface waters 

 are then replaced by subsurface water and sediment, which moves on- 

 shore. Downwelling conditions, conversely, occur as onshore-directed 

 winds transport the surface water onshore. Surface waters are then re- 

 flected by the beach, thus creating offshore-directed return flow of subsur- 

 face water parcels and sediment transport. 



On the west coast of the United States, winds from the south will tend 

 to deflect surface waters in a clockwise direction, or onshore, thus result- 

 ing in downwelling of deeper water parcels. Winds from the north will be 

 deflected offshore, thus resulting in upwelling of deeper water parcels. 

 On the east coast of the United States, upwelling tends to occur when 

 winds are from the southwest, south, or northwest, while downwelling 

 tends to occur when winds are from the northeast (Swift 1976). 



Wright et al. (1986) conclude that northeaster storms create strong, 

 southerly jet-like flows along the mid- Atlantic Bight. These flows affect 

 the floor out to depths as far as -8 m, which results in downwelling and 

 offshore sediment transport. 



Friction-dominated zone 



In the friction-dominated zone, a multitude of mechanisms affect inner 

 shelf cross-shore sediment transport (see previous list of mechanisms of 

 inner shelf cross-shore sediment transport). Overall, Wright et al. (1991) 

 found that incoming incident waves were of primary importance in bed 

 agitation (shear stress) and suspension of sediment on the inner shelf, 

 while near-bottom tide- and wind-induced mean flows were of primary im- 

 portance in the cross-shelf transport of sediment on the inner shelf. 

 Wright et al. (1991) state that this mean-flow-generated cross-shore 



Chapter 3 Evidence of Cross-Shore Sediment Transport 



25 



