Sand Transport 



Consistency runs 



43. The results of nine representative consistency runs are included in 

 this report (Tables 2 and Al) . On the 4 September run, two pairs of traps 

 were used; traps 1 and 2 were located nearest to shore and traps 3 and 4 were 

 located about 12 m farther offshore (Table A2) . Measured fluxes for the two 

 traps are plotted on Figures 11a and lib. The flux decreases approximately 

 exponentially with elevation from the bed. A sharp decrease in flux was found 

 in all deployments of the traps. 



44. The magnitudes of the flux for each pair of traps are approximately 

 equal at any elevation, but corresponding fluxes at the offshore traps were 



4 to 8 times greater (note different x-axis scaling in Figures 11a and b) . 

 The relative magnitudes for any two trap pairs remain in proportion through 

 the lowest three streamers; the highest (fifth) streamers show a sharp 

 decrease in flux. These streamers were probably above water for a large part 

 of the sampling interval. Although the magnitudes of the fluxes at each pair 

 are consistent, taken to be evidence that the streamer trap is reliable, there 

 is still a substantial difference between amounts at any one elevation for the 

 individual traps. Differences at the lowest streamer might arise from 

 differences in scour patterns or from slight differences in elevation of the 

 bottom streamer. However, measured fluxes at the higher elevations should not 

 be affected by scour or by slight differences in streamer height and must 

 therefore reflect the actual transport process. It is concluded that, within 

 a distance of 1 to 2 m across shore, the longshore sand transport rate can 

 differ by at least a factor of 2 under wave and current conditions as 

 encountered in these experiments. Traps placed close together sometimes gave 

 fluxes that were almost identical through the water column, as shown in Figure 

 12 for Run 85909AM6. 



45. In examination of the trapped sand amounts listed in Table Al for 

 the consistency runs, it is seen that the trap with the greatest amount in the 

 lowest streamer has correspondingly greater amounts in the upper streamers, 

 with the exception of one run (85909AM4). The relatively small amount of sand 

 collected by streamer 1 of trap 1 in Run 85909AM4 is believed to be a result 



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