SECT. 3] 



BEACH AND NEARSHORE PROCESSES 



541 



circulation system (Fig. 11a). The pattern that results from this circulation 

 commonly takes the form of an eddy or cell with vertical axis. The positions of 

 the rip currents are dependent on the submarine topography and configuration 

 of the coast, and the height and period of the waves. Periodicity or fluctuation 

 of current velocity and direction is a characteristic of flow in the nearshore 

 circulation system. This variability is primarily due to the grouping of high 



SI NO! J 



SINK 



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Fig. 11. Schematic diagrams of (a) the surface flow in the nearshore circulation system 

 associated with wave action in and near the surf zone. (After Shepard and Inman, 

 1951.) (b) Wave and current relations in the proposed model for longshore transport 

 of sand. 



waves followed by low waves, a phenomenon which gives rise to a pulsation of 

 the water level in the surf zone. 



Measurements in the field, between rip currents, indicate that water in the 

 surf zone has a slow net off'shore flow near the bottom. This flow between rip 

 currents does not extend through the breaker zone ; rather, water outside of the 

 surf zone moves towards the shore. Where beaches are not straight, or where 



