developed in which the flow was started from a smooth-bed condition with 

 either the basin cloths or trap in place, and sand was collected for approx- 

 imately 5 minutes. However, significant scour occurred at the bottom nozzle 

 over the time interval during which the flow speed increased from zero to the 

 final testing flow speed. In contrast, it was found that scour at the bottom 

 nozzle did not occur to such a degree when the trap was placed in a previously 

 established flow. Two slightly different testing procedures for the basin and 

 nozzle tests, outlined below, eliminated both the ripple formation and initial 

 nozzle-scour problems described previously. 



Testing procedure 



a. Basin tests 



(1) A test flow condition was established and setup parameters 

 (aperture diameter of input pipe and height of sluice gate) 

 were recorded . 



(2) The surface of the sand test section was smoothed to a 

 uniform thickness along the length of the section. 



(3) The tank was filled from a vertical flow pipe (located at 

 the far upstream end of the tank) until the sluice gate was 

 overflowed. Slow filling of the tank prevented disturbance of 

 the smoothed sand bed . 



(4) Large sheets of streamer cloth were secured in the basins with 

 tacks at the end of the test section. 



(5) The vertical flow pipe was shut off, and a 2.5-min-long test 

 was run to establish a 'startup' sand transport rate for the 

 test flow condition. Midflow speeds at point A (Figure 21) 

 approximately 6.1m upstream from the basin were recorded 

 during the test. 



(6) After completion of a run, sand collected in the basins was 

 weighed in a drip-free wet condition, which has been shown to 

 be linearly correlated with the dry weight for sand- sized 

 material (Kraus and Nakashima 1986). Selected sand samples 

 were retained for laboratory analysis. 



b. Nozzle tests 



(1) The test flow condition was established and tank setup 



parameters (height of sluice gate, number of seconds input 

 pipe opened) were determined with the trap frame and nozzles 

 to be tested in place. 



51 



