PART IV: CONCLUDING DISCUSSION 



50. Previous field data collection efforts aimed at making direct point 

 measurements of longshore sand transport in the surf zone have either measured 

 the suspended sand concentration, from which a rate must be inferred by taking 

 the product with a longshore current speed, or have used traps to measure only 

 bed-load transport. Neither of these two methods taken individually provides 

 the total transport rate. The SUPERDUCK surf zone experiment described in 

 this report successfully measured the longshore sand flux through the water 

 column as it varied with time at one or two points in the surf zone. 



51. The portable streamer traps developed in this project were found to 

 give reliable and consistent results by comparison of sand fluxes obtained 

 with traps placed close to each other. The consistency ratio, calculated by 

 dividing the lower value of the transport rate density for a particular run by 

 the higher value for that run and multiplying by 100, ranged from 50 to 100 

 percent for the SUPERDUCK consistency tests. Of the 14 vertical distributions 

 of sand flux, the majority of the shoreward and seaward consistency test data 

 sets had similar coefficients and were described by a power— law equation. 

 These favorable comparisons between magnitudes of the transport rate densities 

 and the shape of the vertical flux distributions obtained at two closely 

 spaced traps indicate that the streamer trap and nozzles are indeed consistent 

 and provide reproducible measurements of the transport rate. 



52. The transport rate density measured at SUPERDUCK was found to be 

 closely related to the product of wave height and longshore current speed, 

 consistent with previously derived theoretical models of transport. The 

 correlation was considerably improved, however, by including corrections due 

 to energy dissipation introduced by breaking waves and the variation in the 

 longshore current speed. 



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