PART III: HYDRAULIC EFFICIENCY TESTS 



29. Experiments were conducted in a unidirectional flow tank to 

 evaluate the hydraulic and sand- trapping efficiencies of streamer trap sand 

 collection elements of various nozzle types, streamer length, and cloth mesh 

 size. For comparison, hydraulic and sand-trapping efficiencies were also 

 evaluated for the H-S sampler, a popular pressure-difference bed-load trap 

 developed for use in the riverine environment (Helley and Smith 1971, Druffel 

 et al. 1976, Emmett 1980, Hubbell et al. 1985, 1987) (see Appendix A). A 

 unidirectional flow tank was used to simulate the quasi -steady state longshore 

 current that drives longshore sand transport in the surf zone. It would be 

 most realistic to conduct the tests in a cross-flow facility to simulate wave 

 action or oscillatory motion orthogonal to the unidirectional flow. However, 

 facilities of the scale required to test a prototype streamer trap do not 

 exist. 



30. Twenty- three streamer trap nozzle variations were tested to 

 determine nozzle parameters defining optimal hydraulic and sand- trapping 

 efficiencies. This chapter describes the facility used for the experiments, 

 the streamer elements tested, and results from hydraulic efficiency experi- 

 ments. Results of similar sand- trapping tests are given in Part IV. 



Description of Facility and Equipment 



Tank 



31. Both the hydraulic and sand- trapping tests were conducted in an 

 18.3-m-long unidirectional flow tank with a cross-sectional area of 0.76 m by 

 0.76 m and a maximum water discharge of 0.2 m 3 /sec . The tank sides are made 

 of iron panels bolted together, except for a plexiglass viewing section 

 approximately 4.6 m in length located in the middle of the tank (Figure 7). 

 Prior to the experiment, joints between adjoining panels were filled with 

 caulk and smoothed to minimize turbulence and flow separation at these 

 indentations in the tank walls. Nevertheless, small -amplitude ripples did 

 form at the seams (Figure 8). Water used in the testing was supplied by a 

 circulating system, and discharges in the model were measured with venturi 



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