PART IV: CONCLUDING DISCUSSION 



51. Previous field data collection efforts aimed at making 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 

 bedload transport. Neither of these two methods taken individually provides 

 the total transport rate. To the authors' knowledge, the DUCK85 surf zone 

 experiments described here were the first to directly and synoptically measure 

 the longshore sand flux through the water column and across the surf zone in 

 the field or the laboratory. Although the DUCK85 field data collection 

 project was originally aimed to be a test of equipment and procedures, a 

 considerable amount of high-quality data was obtained under the ideal wave, 

 current, and sediment transport conditions encountered. 



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

 give reliable and consistent results by comparison of fluxes obtained with 

 traps placed close to each other. Measured cross -shore distributions did not 

 show anomalous or peculiar shapes, but agreed with previous results in a 

 qualitative way. Uniform (flat) cross-shore distributions predominated in 

 these experiments, although peaked shapes were occasionally found. The 

 transport rate was effectively zero immediately outside the wave breaker zone. 

 Vertical distributions of the sand flux decreased sharply with elevation from 

 the bed and had an approximate exponential shape independent of position in 

 the surf zone. Total surf zone transport rates correlated reasonably well 

 with a simple parameter related to the average longshore discharge of water. 



53. Although portable traps appear to be a primitive means to measure 

 the sand transport rate, they have numerous advantages, including low con- 

 struction and maintenance costs, capability to directly measure the sand flux 

 both at the bed and in the water column, ease of movement in the surf zone to 

 obtain point measurements where desired, and an averaging or measurement 

 interval compatible with engineering theories and models of sand transport and 

 beach change. The limitations of traps must also be kept in mind. In 

 general, they work best in conditions where the flow does not reverse, and 



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