Sonu (1972) was the first to publish vertical velocity profiles from 

 field measurements. Figure 3 shows values based on 2-minute averages in a rip 

 current. Other similar profiles generally showed larger currents near the bed 

 at the root (nearshore) with the maximum velocity moving upward farther sea- 

 ward. Variations in current at three depths and three surf zone positions on 

 the eastern Lake Michigan shoreline were measured by Wood and Meadows (1975). 

 A summary of their work (Meadows, 1976) discusses time-dependent currents and 

 says little about the vertical variations measured. A time history is shown 

 in Figure 4. The average current is in the same direction but lower near the 

 bottom. Brenninkmeyer , James, and Wood (1977) used two bidirectional EM 

 current meters in the Massachusetts surf. The onshore-offshore direction was 

 measured at two elevations. Four possible bore-backwash interaction patterns 

 were observed along with the interactions of the bores themselves. Extremely 

 complex three-dimensional flows result that also pulsate in time 

 (Brenninkmeyer, 1978). In one figure in Brenninkmeyer, James, and Wood 

 (1977), the upper current meter showed 6.6 meters per second onshore at the 

 same instant a meter 15 centimeters below read 1.3 meters per second onshore. 

 At other times the directions were reversed. 



Zenkovich (1967) summarizes Russian thinking through 1960 and argues for 

 a three-dimensional velocity structure in the nearshore zone. Most coasts 

 were thought to have a bottom return flow which resulted in unstable, compli- 

 cated circulation patterns with a horizontal axis. Less stable circulations 

 with a vertical axis produced rip and gradient currents. No general picture 

 of coastal hydrodynamics was felt possible at that time, due to complex and 

 diverse boundary conditions and the instabilities involved. 



SEACROVE, FLA. 

 JULY 31, I96S 



Figure 3. Velocity profile in a rip current at Seagrove, Florida, July 

 1968 (from Sonu, 1972). 



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