small , thereby tending to increase the relative percentage of sand flux in the 

 upper nozzles. 



82. Either an exponential or a power law fit to the vertical distribu- 

 tion of sand flux could be used to mathematically interpolate for fluxes 

 between adjacent nozzles. However, because only three vertical point 

 measurements were available to fit the curves, this procedure was found to 

 either over- or under-predict point measurements of sand flux by as much as 

 100 percent. 



83. Because methods of integrating the vertical distribution of sand 

 flux through the water column introduced unacceptable error into the data 

 analysis, another approach was used to calculate sand-trapping efficiencies 

 for the nozzles. It was assumed that nozzles collecting only suspended 

 material (all those except the bottom nozzle) had a sand-trapping efficiency 

 equal to their hydraulic efficiency. This procedure is considered reasonable 

 for a quasi -steady unidirectional flow condition, implying that suspended sand 

 behaves in the same manner as the fluid particles. This assumption should be 

 acceptable for the grain sizes and flow conditions found on typical sandy 

 beaches. However, bed load and saltating material near the bed were observed 

 to move at lower speeds than the fluid flow. This characteristic of sand 

 movement near the bed as well as the potential for scour near the lower edge 

 of the bottom nozzle prohibited assigning a hydraulic efficiency equal to the 

 sand- trapping efficiency to these lowest nozzles. Fluxes for the bottom 

 nozzles and basin were calculated and compared using 5 cm as the maximum 

 vertical elevation from the bed for significant (at least 96 percent of the 

 total) sand transport. Sand fluxes for the bottom nozzles were then compared 

 directly to the basin sand- trapping fluxes. It is noted that the 5-cm 

 elevation delineating significant sand transport pertains to the present 

 laboratory conditions and is not considered to be a general result. 



Results 



84. All nozzle and basin tests indicated increasing sand flux as 

 midflow and bottom flow speeds increased. Four types of equations were fit to 

 the transport rate data sets using the midflow and bottom flow speeds as the 

 independent variable: linear, exponential, power, and a power fit incorporat- 

 ing the threshold midflow or bottom flow speed. Because of the short time 



56 



