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You are here : eLibrary : IAHR World Congress Proceedings : 36th Congress - The Hague (2015) ALL CONTENT : Water engineering : Boundary layer development in roughness layer at modeled armored gravel bed stream and the sand move...
Boundary layer development in roughness layer at modeled armored gravel bed stream and the sand movement in the region
Author : NORIO TANAKA (1), (2), YUTA YOSHIZAWA (3), SAQIB HABIB (4)
ABSTRACT
Sediment supply to downstream of a dam by dredging sediment in a reservoir and placing sediment in a downstream flood
basin of the river is recently tested for solving a riverbed environmental problem caused by armoring. Although the threedimensional
turbulence structures at the armored bed are assumed to greatly affect the invertebrate dynamics, not much
studies have been conducted especially for armored bed and the relative water depth to gravel or stone size is small.
Experiments were conducted in a flume with14 m in length and 0.5 m in width for clarifying the turbulence structure and
shear stress characteristics around and inside the armored layer, sand motion in the armored layer, and effect of boundary
layer development on the velocity distribution. For expressing the sand movement in armored layer, three size gravel were
selected. Firstly, 1.6 cm average diameter gravel with a thickness of 3.5 cm (Group-2) was placed on bed, and secondly,
10 cm stone with a density of 68 stones/m2 (Case1) and 43 stones/m2 (Case2) (Group-1) was put on the Group-2. The
relative water depth to stone height was set as 3 and 4 for Case1 and Case2, respectively. Particle image velocimetry was
used for obtaining the turbulence structure in and around the bed layer. Velocity distribution and Reynolds stress were
obtained by time and spatial-averaging the visualized velocity field in totally 5 sections and stream-wise spatial turbulence
structures were obtained. With the small relative water depths condition, the form-induced sublayer is thick and log-law has
been found not to be applied. The roughness layer width becomes thin with the development of boundary layer. Compared
with the Case 1, the sand movement in the roughness layer is very rapid in Case2. This is due to the difference of the flow
structure in the roughness layer.
File Size : 7,073,803 bytes
File Type : Adobe Acrobat Document
Chapter : IAHR World Congress Proceedings
Category : 36th Congress - The Hague (2015) ALL CONTENT
Article : Water engineering
Date Published : 19/08/2015
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