Polytatir Slave Cloth Stratmar 



Stainlass Rod 

 0.64 cm (0.25 InJ ^ 





Figure 7. DUCK85 streamer nozzle 



23. Based on the results of a uniform-flow tank experiment conducted 

 following the field project (Rosati and Kraus 1988), the streamer trap nozzle 

 used at DUCK85 is no longer recommended. This test examined the hydraulic 

 efficiencies of 22 generic nozzle configurations plus several variations and 

 led to an improved design that has been used in later field data collection 

 projects such as SUPERDUCK. 



24. In addition, sand- trapping efficiency tests in uniform flow were 

 performed in another series of experiments (Rosati and Kraus in preparation) 

 for a small number of nozzle configurations which had near optimal hydraulic 

 efficiencies, including the DUCK85 nozzle. It was found that the DUCK85 

 nozzle had a sand-trapping efficiency near unity (0.92) for suspended sand, 

 but a much lower efficiency for a nozzle resting on the bed (0.13). The small 

 value (0.13) of the bed -load trapping efficiency (which includes suspended 

 load within 9 cm of the bottom) is caused by scour and the scour hole created 

 under the nozzle, allowing sediment to pass under it. Other nozzle designs, 

 which replace the 1/4-in. rods with sheet metal hoods essentially eliminate 

 this problem for uniform flow conditions. The actual efficiency of the 



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