PART VI: CONCLUSIONS AND RECOMMENDATIONS 

 Conclusions 



125. The objectives of this study were to evaluate and improve upon the 

 hydraulic and sand- trapping characteristics of the streamer trap nozzle for 

 use in the nearshore zone. Twenty- three variations of the streamer trap 

 nozzle were initially evaluated to determine their hydraulic characteristics, 

 and three streamer trap nozzles with near-optimum hydraulic efficiencies were 

 subsequently tested to qualitatively and quantitatively determine their sand- 

 trapping characteristics. The H-S sampler, a pressure-difference riverine 

 sediment trap extensively reported on in the literature, was also tested in 

 both the hydraulic and sand- trapping phases of the experimental program for 

 comparison with both streamer trap nozzle results and reported efficiencies. 



126. One hundred and seventeen hydraulic and 101 sand-trapping effic- 

 iency tests were performed. Both the hydraulic and sand-trapping tests were 

 conducted in a unidirectional flow tank with the objective of simulating the 

 longshore current in the surf zone. Hydraulic testing of the nozzles involved 

 measuring flow speed at the nozzle and then repeating the measurements for the 

 same flow condition at the same location in the tank without the nozzle in 

 place. By dividing the flow speed in the nozzle by the ambient (without 

 nozzle) flow speed, a measure of hydraulic efficiency was obtained for the 

 particular flow condition. For nozzles with near-optimal hydraulic efficien- 

 cies, measurements were made for four flow conditions (midflow speeds equal to 

 22, 43, 59, and 74 cm/sec) with one nozzle located at the bed or at the mid- 

 flow elevation, and with two nozzles in place (one at the bed and the other at 

 a midflow elevation) . 



127. The sand- trapping tests primarily consisted of measuring ambient 

 sand flux (with a pit sampler) for a range of midflow speeds (ranging from 46 

 to 74 cm/sec) and comparing values of ambient flux to nozzle-predicted sand 

 flux. Sand with a median grain size of 0.23 mm was placed in a test section 

 built into the testing tank. Because of a presumed disequilibrium of sand 

 transport between the trap testing section and the pit sampler, measurements 

 of ambient transport were not comparable to the nozzle-predicted sand flux. 



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