procedures. However, the wave, current, and sand transport conditions proved 

 to be ideal, and a large amount of data was collected. 



Sand Transport Measurement Methods 



6. Three methods were considered for measuring the transport rate at 

 the DUCK85 field data collection project; sand tracers, impoundment at 

 temporary or permanent obstructions, and traps. In preparation for DUCK85, 

 Kraus (1987) surveyed available measurement methods and concluded that traps 

 offered the best means to obtain transport rate data compatible with the 

 accuracy and detail required by existing nvunerical models which simulate beach 

 evolution. Traps were also determined to be the least expensive of the three 

 methods, yielding the highest data-point-per-dollar ratio. 



7. Portable traps allow measurement of the vertical distribution of the 

 transport rate (i.e., transport at the bed and in the water colximn) , and 

 simultaneous deployment of traps at intervals across the surf zone enables 

 measurement of the cross -shore distribution of the longshore transport rate. 

 Traps measure the sand flux, a quantity directly related to the transport 

 rate, and not simply a sediment concentration. As in concentration measure- 

 ments , transported particles are automatically retained by the traps and made 

 available for analysis. Traps collect the material that actually moves, 

 including sand, shell fragments, and other particles of size nominally larger 

 than the trap mesh, and no assumptions need be made about grain size, as 

 required in tracer studies. Mean wave and current conditions in the surf zone 

 typically change on the order of minutes, and traps are well suited to such a 

 sampling interval as opposed to tracer and impoundment methods. Traps are 

 also inexpensive to construct and maintain, and only a minimum amount of 

 training is necessary to use them. 



8. Traps have disadvantages, notably potential for scour and restric- 

 tion to use in surf zones with significant breaking wave heights on the order 

 of 1 m or less. A laboratory experiment program was initiated to examine the 

 hydraulic efficiency (Rosati and Kraus 1988) and sand trapping efficiency 

 (Rosati and Kraus in preparation) of the trap used in this field program to 

 understand its characteristics and to optimize the design. 



