1.0
Standard Deviation
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0
5
10
15
20 25 30 35 40
45
50
55
60
Load Cell No. (1-60)
Figure 25. Standard deviation of load cell readings measured during tare-weight
tests conducted with the traps empty and the facility drained
Two other tests were performed with the facility completely drained to assess
the accuracy of the weight recorded by each trap. The first test involved placing
a known weight of approximately 120 kg at the upstream end of the trap. The
total weight in the trap was measured and compared to the total weight measured
when the weight was placed at the center, and finally the downstream end of the
trap. This process was repeated for the 20 traps. This test was conducted to
assess the effect of various distributions of sand along the length of the trap.
Results showed that the maximum variation in the sum of the three load cells, for
all three positions, did not exceed 0.5 kg, a maximum error of less than
0.5 percent.
The final test conducted with the traps empty and the facility drained
involved placing the known weight of 120 kg in the center of Trap No. 1, and
then repeating the measurement for each of the 20 traps. The error in the total
weight recorded in each trap was less than 1 kg from the known weight of 120
kg, which is considered to be excellent. The results of these tests showed that the
20 sediment traps are very consistent and accurate with the traps empty and the
facility drained.
Removing air bubbles from beneath the rubber seals
A number of tests were performed with the wave basin filled to a water depth
of 0.9 m, the normal operating water level for the moveable-bed experiments.
The traps were completely submerged and filled with water. As the facility was
being filled, it was observed that air bubbles would rise to the surface,
43
Chapter 4
Sediment Trapping and Dredging Systems
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