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18. SUBJECT TERMS (Continued), 



Apparatus 



Helley-Smith sampler Sand .trap 



Laboratory experiment Sediment trap 



Longshore transport Sediment transport 



Riverine transport Transport rate 



19. ABSTRACT (Continued). 



period. The SUPERDUCK nozzle, previously used in the SUPERDUCK field data collection 

 project, performed near optimally at an off-bed elevation in the laboratory. When 

 the nozzle was positioned at the bed, scour occurred at the base over approximately 

 half the testing period. A new cube-shaped nozzle design performed near optimally 

 at both off- and on-bed elevations in the laboratory. Hydraulic efficiencies measured 

 in the laboratory for the Helley-Smith sampler were comparable to those reported in 

 the literature; however, transport processes with the sampler located on the bed were 

 distorted and deviated greatly from the normal patterns of sand movement in the tank 

 tests. Field testing of the DUCK85 and SUPERDUCK nozzles indicated that both nozzle 

 types were reasonably consistent, assuming that the transport rate was uniform over 

 the region occupied by the traps. On the basis of this testing program, portable 

 traps are recommended as a reliable and accurate method of measuring sand transport 

 under low to moderate wave energy contitions. 



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