Sand transport at the basin was less than at the trap testing area. 

 To evaluate this effect, two runs were made with the C nozzle 

 placed at the first basin for midflow speeds equal to 51.6 and 66.1 

 cm/sec. The sand flux for the bottom C nozzle at the basin for the 

 two tests was less (48 and 19 percent, respectively) than equation- 

 predicted fluxes for the same flow rate (Figure 34). The test at 

 the higher flow condition was approximately equal to the lower 95 

 percent confidence limit, indicating that sand flux at the basin 

 did vary significantly (with 95 percent confidence) than sand flux 

 at the trap testing area, at least at the higher flow condition. 

 The differences between C nozzle fluxes measured at the basin and 

 predicted fluxes using the modified 5.0-min basin threshold power 

 equations (Equations 15 and 18) indicate that the C measurements at 

 the basin were within the 95 percent confidence interval for the 

 basin data. 



Suspended material passed over the basins at the higher flow 

 speeds. A qualitative evaluation of basin efficiency presented in 

 a previous section (see "Evaluation of basin efficiency") concluded 

 that the basins were highly efficient. The quantities of sand 

 collected above the bottom C nozzle for the 51. 6 -cm/sec midflow 

 speed test described in c were greater (4.1 percent) than observed 

 for the C nozzle data set (Table 5). However, the 66.1-cm/sec 

 midflow speed test percentage of suspended sand was not signifi- 

 cantly greater (1.7 percent), contrary to an expected increase in 

 suspended sand at higher flow speeds. Apparently, the 4.1 percent 

 of suspended sand collected above the bottom nozzle during the 

 lower flow speed test is an anomaly. Sand samples from both nozzle 

 and basin tests were sieved to provide some indication of whether 

 the C nozzle did collect finer material (hence suspended sand) that 

 was not collected in the basins. The median grain size for the 

 bottom C nozzle for five samples analyzed was 0.29 mm, equal to the 

 median grain size for the SUPERDUCK nozzle and larger than the 

 median grain size for the DUCK85 nozzle (0.27 mm) and basin (0.26 

 mm) . A larger median grain size for the C nozzle would indicate 

 that the nozzle did create a pressure difference, collecting more 

 material than was actually being transported. The H-S sampler 

 created local flow speeds greater than the ambient flow speed and 

 therefore was able to entrain and collect larger -sized material 

 (median grain size for H-S = 0.33 mm). However, sand collected in 

 midflow C nozzles was also coarser than that collected in the 

 SUPERDUCK midflow nozzles (C = 0.26 mm; SUPERDUCK = 0.19 mm), 

 indicating that the sand in the test section was generally coarser 

 during the C nozzle tests which were conducted near the end of the 

 experiment program. 



Sand transport during all trap tests was higher than during basin 

 tests due to a systematic error. As discussed in item c above, one 

 test conducted with the C nozzle located at the basin gave sand 

 transport rates less than that of the C nozzle tests at the trap 

 testing area. Therefore, a systematic error did not occur 



72 



