given size in such a fluid in a quiescent state. Since the density and 

 viscosity of the water were constant, it follows that the differences in 

 Reynolds number between particles were determined by their settling 

 velocities (which in turn depended on the nominal diameter and specific 

 gravity of the particles). Thus, the determinations of the Reynolds 

 number are based directly on the settling velocity of the particles. 



The numerical magnitude of the Reynolds number conveys the relative 

 significance of the inertial ( V p x d n ) and viscous (V) forces in action. 

 Reynolds numbers less than 0.001 say, would make one confident in ignoring 

 inertial forces. Reynolds numbers higher than 1,000, on the other hand, 

 would suggest that viscous forces might be ignored (although in reality 

 these can never be entirely ignored). The results of this investigation, 

 however, did not yield Reynolds numbers of such low or high magnitudes. 

 The majority of our values ranged between 2 and 15 (Table 5). 



Because the sediment sizes involved ranged around 0.250 - 0.300 mm , 

 a predominance of inertial forces was expected. The viscosity of the 

 water at the low temperature encountered at the time of sampling, however, 

 was high enough to significantly reduce the magnitude of R e . Not only are 

 the Reynolds numbers found relatively low but they fall within the range 

 where laminar flow changes into turbulent flow, i.e., inertial forces take 

 significant prominence over viscous forces. At Reynolds numbers above the 

 range of Stokes' Law (R e = 2, as extended by Oseen and Goldstein) the flow 

 lines around the particle separate from the particle surface and enclose a 

 discontinuity; a wake or low-pressure zone is formed. When this separation 

 is well formed, inertial forces predominate significantly. But this trans- 

 formation to significant predominance of inertial forces is gradual. The 

 zone of separation has a poorly defined appearance at R e = 3 but gradually 

 takes on a more clearly defined appearance as the Reynolds number is in- 

 creased until at R e = 20 the separation zone has a well-defined vortex 

 downstream from the particle (Schulz, et al., 1954). It should be noted 

 that within the range of R e = 3, to R e = 20, inertial forces are definitely 

 greater than viscous forces, but the viscous forces still exert a signi- 

 ficant influence in retarding the motion of the particles through the fluid. 



The effect of the high kinematic viscosity of the sea water in lower- 

 ing the magnitude of Re (and consequently increasing that of Cq) resulted in 

 most of the sand grains exhibiting dynamic properties more akin to those of 

 much finer grains which are subject to greater drag resistance. At the 

 same time their dynamic behavior was not much different from that of 

 perfect spheres since at these low Reynolds numbers the drag resistance on 

 particles with S.F. = 0.7 and S.F. = 1.0 (as indicated by Cd values in 

 Table 1) is almost identical. 



The distribution of Reynolds numbers along the different beach zones 

 in the three transects follows closely the distribution pattern of mean 

 size values, as expected from the relationship between these two parameters. 



19 



