Experimental study on evaluation of grain diameter using contact time in flow

Experimental study on evaluation of grain diameter using contact time in flow

The diameter of bed load sediment is measured directly using bed load samples. However, it is expensive to transport sediment from the field to the laboratory and to measure the diameter using the sieve test in the laboratory. Indirect methods of estimating gravel size have been evaluated, including photographs of a dry river bed and using the sound of gravel colliding with a steel pipe called a hydrophone. However, these methods are difficult to evaluate gravel size. Therefore, we proposed a simple, low cost method for measuring the diameter of bed load sediment in a river. Proposed method requires the contact time between sediment and a square acrylic pillar. The contact time was measured in a flume experiment. We examined whether the diameter of sediment could be estimated using the relationship between the contact time and gravel diameter. In addition, the maximum signal wave height and collision velocity were used to estimate the gravel diameter. The results were as follows:(1) the relationship between the maximum signal wave height and gravel diameter was not clearly observed in this experiment;(2) the collision velocity was not correlated with the contact time; and (3) the nature of the gravel movement, i.e., meandering or straight, changed with the depth:diameter ratio.