Bed-Load Transport and Bed Variation in an Open Channel With Multiple Rows of Cylinders

Abstract

The roles of forest along the river bank have been noted from the view point of the river environment and flood disaster. Bed load transport and sediment deposition are experimentally examined in an open channel with cylinders installed across the whole channel width in their multiple rows. Cylinders were placed in stagger with their equal spacing on the bed.The transport rate of bed load was measured on the movable bed. The bed-load transport rate was found less than that in an open channel without cylinders. Effcetive friction velocity was found from the comparison of the measurement of bed-load transport rate with a transport rate equation. The transport rate of bed load and the non-dimensional average velocity decrease with the arrangement density of cylinders.Sediment deposition profiles were also measured. In the case of larger density of cylinder arrangement, sediment deposition occurs in the upper stream reach, while, in the case of smaller density, sediment deposition occurs in the downstream reach. The comparison of the calculation and the experiments shows good agreement.

Effect of tall vegetation on sediment transport by channel flows

“…This study is an extension of previous investigations by Hirano et al (1999) and Hashimoto and Park (2003) on the sediment transport by flows through vegetation, and by Kothyari et al (2009) for quantification of the stem drag. The sediment transport is examined herein in an open channel with multiple rows of stems (cylinders) installed uniformly over a wide range of bed slopes and bed material size.…”

“…The quantitative research on flow, vegetation and sediment interaction began in Japan with the works of Ishikawa et al (1998) and Hirano et al (1997Hirano et al ( , 1999. Hirano et al (1997) investigated drag coefficients of model tree groups in sediment-water mixture, whereas Ishikawa et al (1998) and Hirano et al (1999) investigated sediment transport within a model tree area to examine the tree effect on sediment transport.…”

“…Hirano et al (1997) investigated drag coefficients of model tree groups in sediment-water mixture, whereas Ishikawa et al (1998) and Hirano et al (1999) investigated sediment transport within a model tree area to examine the tree effect on sediment transport. Hirano et al (1999) used sand of relative density G = σ/ρ = 2.61 ∼ 2.65 and median grain diameter d 50 = 0.55, 0.84, and 1.9 mm, respectively, as bed materials. Here σ = sediment mass density and ρ = fluid mass density.…”

“…The type of sediment transport was bed load. Using their observations, Hirano et al (1999) numerically predicted sediment deposition in the model-tree area. The main test limitation was the short channel of less than 6.0 m. No investigations have succeeded as yet in the exact evaluation of the effect of trees on the sediment transport for θ > 3.03 • despite such angles occur frequently in nature.…”