1991 Fiscal Year Final Research Report Summary
Effects of vegetations on river flow and channel cross section
| Project/Area Number |
01550398
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Hydraulic engineering
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| Research Institution | Tokyo Institute of Technology (1990-1991)
Saitama University (1989) |
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Principal Investigator |
IKEDA S. Tokyo Institute of Technology, Dept. of Civil Eng., Professor., 工学部, 教授 (60016590)
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| Co-Investigator(Kenkyū-buntansha) |
ASAEDA T. Saitama Univ., Dept. of Foundation Engineering. Assoc. Professor., 工学部, 助教授 (40134332)
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| Project Period (FY) |
1989 – 1991
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| Keywords | Vegetation / Flow retardation / Transverse diffusion / Sediment transport / Gravel rivers / Sand rivers / Suspended sediment / Horizontal vortices |
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| Research Abstract |
Effect of bank vegetation on the stable channel cross-section of straight gravel rivers is studied theoretically, in which singular perturbation and matched asymptotic expansion techniques are bmployed to derive the lateral distributions of depth-averaged fluid velocity and the bed shear stress. A condition of sediment incipient motion is imposed at the junction of the bed and the banks to derive the stable depth, and a formula for resistance to flow is used to obtain the stable width. It is revealed that a thicker vegetation yields a larger depth and a smaller width. Increasing discharge is found to increase the effect of vegetation. The analysis is found to agree reasonably well with available field data.
The influence of bank vegetation on the stable channel cross-sectional geometry of stable, straight gravel rivers is studied theoretically. Singular perturbation and matched asymptotic expansion techniques are employed to derive the lateral distribution of depth-averaged fluid veloci
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ty and the bed shear stress. A condition of sediment incipient motion is imposed at the junctions of the bed and the banks to derive the stable depth, and a formula for resistance to flow is used to obtain the stable width. The theory reveals that a thicker vegetation yields a larger depth and a smaller width. Increasing discharge increases the effect of vegetation. The analysis agrees reasonably well with available field data.
A mathematical model for dctining latcral distributions of fluid velocity and suspended sediment concentration in straight channels with pile dikes near the banks is pi-escnted. Singular perturbation and matched asymptotic expansion techniques are employed to derive the distributions. It is found that suspended sediment is transported toward the pile dike region due to lateral turbulent diffusion. the amount of which is predictcd by the tiicory. Laboratory work has revealed that the lateral diffusivitics of fluid momentum and suspended sediment are identical with those observed for flows without pile dikes. The vertical diffusivity of suspended sediment is found not to be affected by pile dikes. The laboratory tests support the present model. Less
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