exclusively for the trap tests, as a large difference was measured 

 with the same trap nozzle at two different locations. 



100. One theory that may explain the discrepancies in sand flux measur- 

 ed at the trap testing area compared to fluxes at the basin (see item c) is 

 that the trap testing area was located in the test section such that flow 

 conditions had not equilibrated with the sand bed. Large eddies potentially 

 caused by the transition from the test section ramp to the sand bed at the up- 

 f low end of the tank may have entrained more material , thereby creating an 

 artificially high transport rate at the trap testing area (Figure 36). At the 

 far end of the test section, the basin could have been outside the "equilib- 

 rium length" of the test section where sand transport had reached an equilib- 

 rium state as the eddies were reduced. If this were the case, the 2.4- by 

 0.67-m area between the trap testing area and basin area would have increased 

 in elevation by sand deposition. The wet-weight density of sand used in the 

 experiment program was calculated as 3.42 g (wet)/cm 3 using the density of 

 quartz sand (2.65 g (dry)/cm 3 ) and the relationship between wet and dry weight 

 determined empirically (0.78 g (dry)/1.0 g (wet)). Using fluxes obtained with 

 the C nozzle at the basin and predicted fluxes, for the same flow rate, and 

 assuming that the accreting sand would settle out evenly over the 2.4- by 

 0.67-m area, the increase in bed elevation calculated using the wet weight 

 density would have been too slight to observe (0.02 and 0.04 cm). Even the 45 

 percent discrepancy between the C nozzle and basin fluxes at the highest flow 

 speed would have created only a small increase in elevation (0.06 cm). 



Decision on Ambient Sand Transport Rate 



101. It is concluded that the basin sampler, possibly partially due to 

 the nonequilibrium length of the test section, did not provide an adequate 

 measure of the ambient sand transport rate. Therefore, fluxes measured with 

 the bottom C nozzle were used as a standard measure of the ambient sand 

 transport rate. It is recognized that by using sand fluxes obtained with the 

 C nozzle as the measure of ambient transport that the original standard of 



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