10. Trap development and applications for use in the nearshore have not 

 been extensively investigated, as opposed to other apparatus and instrumen- 

 tation. Therefore, it is worthwhile to investigate this technique because it 

 appears to hold promise as a method of obtaining accurate estimates of 

 sediment transport under a certain range of environmental conditions. In the 

 nearshore, sediment consists primarily of sand-sized quartz particles (grain 

 diameters in the range of 0.074 to 1.0 mm); therefore, discussions to follow 

 will focus on particles in the sand range. However, the basic principle of 

 trapping is applicable, with certain modifications and restrictions, to almost 

 any size sediment particles . 



Sand traps 



11. The use of traps to estimate sand transport rates and collect a 

 representative sample of moving material has been limited in coastal engin- 

 eering. However, the study and use of traps in the riverine environment has 

 been documented since 1808 (see Appendix A). In the United States, the most 

 comprehensively studied riverine trap is the Helley- Smith (H-S) sampler 

 (Helley and Smith 1971) (Figure 1). The H-S sampler is a direct-measurement 

 trap designed to rest on the river bed and sample bed load. The sampler 

 consists of an expanding metal nozzle connected to an inflexible mesh cloth 

 bag which retains the collected material. Designed to eliminate a possible 

 decrease in water speed at the sampler entrance, the expanding nozzle creates 

 a pressure difference between the entrance and exit regions of the trap. 

 Thus , the intake rate is controlled by the nozzle geometry and is effectively 

 constant, independent of the amount of sediment in the collection bag. 



12. The streamer trap is a sand trap recently developed for use in the 

 coastal zone (Katori 1982, 1983). Similar to the H-S sampler, the streamer 

 trap uses a mesh cloth bag attached to a metal nozzle to collect sand. 

 However, the streamers are light and can be mounted vertically on a metal 

 frame (Kraus 1987) so that sand moving in suspension can be collected at any 

 point in the water column (Figure 2). Streamer traps have recently been used 

 in major field data collection projects in the surf zone to estimate longshore 

 sand transport rates (Kraus 1987; Kraus and Dean 1987; Kraus, Gingerich, and 

 Rosati 1989; Kraus, Gingerich, and Rosati in preparation). Placement of 

 several streamer traps across the surf zone results in a measurement of the 



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