Characteristics of Sediment Trapping by the Bamboo Sampler

Abstract

Suspended sediment in the sea often troubles improvement and development of coastal fishing ground. But quantitative measurement of sediment remains a difficult problem. Bamboo samplers, which have been frequently used in Japan, could not show the quantitative characteristics of the sediment, either. Because the relation between the amount of sediment trapped in the sampler and the amount of sediment in the sea was unknown. Some studies on the bamboo sampler have been carried out in order to show this relation directly. But few investigations have been performed from the point of view of the trapping mechanism of bamboo sampler.
In this paper, in order to obtain the basic data of analysing the mechanism, simplified experiments in steady flow were performed. In the experiments, two-dimensional models of bamboo sampler were used and spherical glass particles were suspended in the steady flow. The authors make the assumptio that sediment particles go forward as they go downward by gravity in steady flow passing through the hole of bamboo sampler. With this assumption, the efficiency of capture F can be written as the following equation. F=S^f/S_i=d/a•w/v where S_f is the weight of sediment which is trapped in the sampleer, S_i is the weight of sediment which flows into the sampler, a is the height of the hole, d is the diameter of the sampler, w is the fall velocity of the particles and v is the current velocity. F were measured in various cases in which the values of a, d, w, v were varied.
The results calculated from the above formula agreed well with the experimental values.