• Ecology and Resilient Infrastructure
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• v.5 no.4
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• pp.199-209
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• 2018

In river design, consideration of bed shear stresses is necessary to secure stability of levee and floodplain. In this study distributions of bed shear stresses in compound open channels are analyzed through numerical simulation for various width and depth. LES solver in OpenFOAM is applied to 12 cases of compound channel shapes considering secondary flow which effects distributions of bed shear stresses. By the results time averaged velocity distributions, secondary currents, and distributions of bed shear stresses are analyzed. Overall distributions of bed shears in floodplain show that higher shear stresses are seen in left of floodplain and the shears decrease toward right of floodplain. However, high local variations in shear stresses are shown due to the secondary flow effects. In shallow floodplain, bed shear stresses show low value below 0.8 times of averaged bed shear. In deep floodplain, bed shear stresses show high value over 1.2 - 1.4 times of averaged bed shear.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.09a
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• pp.360-361
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• 2005

• Ecology and Resilient Infrastructure
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• v.4 no.4
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• pp.207-215
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• 2017

Hydraulic issues such as flow resistance, side wall correction, sediment, erosion and deposition, and channel design have close relation with distribution of bed shear stresses but the measurement of the distribution of bed shear stresses is not easy. In this study the Preston tube which makes possible relatively simple measurement of bed shear stresses is used to analyze the characteristics of bed shear distribution in compound open channels with different depth ratio. The Preston tubes are made and calibrated to develop the calibration formula and then they are applied to measure bed shear stress distribution in 5 cases depth ratio condition of compound channels. The results are compared with former experiment data, and characteristics of bed shear stress distributions are studied with different channel scales and Reynolds numbers. Although bed shear distributions with depth ratio show overall agreement with former studies, some differences are verified in bed shear variation, formation of inflection point in main channel, and distribution near floodplain junction which are due to high Reynolds number. Through the study applicability of the Preston tubes are also verified and characteristics of bed shear distribution in compound channels are suggested with Reynolds number and depth ratio.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.6B
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• pp.607-615
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• 2010

Vegetation drag tends to raise water level by retarding the flow. Previous studies have focussed on either the vertical structure modeling or the one-dimensional modeling, which can hardly be used to simulate the vegetative streams in practical engineering. Therefore, this paper presents a two-dimensional numerical model based on the depth-averaged flow equations. Vegetation drags are reflected in the flow equations, assuming non-flexible rigid cylinders. For validations, flow properties measured in both rectangular and compound channels are compared with simulated data, showing good agreement. Then, the model is applied to a reach in the Han River and the impact of floodplain vegetation on the flow is investigated.

• Journal of Korea Water Resources Association
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• v.44 no.2
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• pp.157-167
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• 2011

A numerical model was developed to predict the stage-discharge curve and lateral distribution of unit discharge in open channels with nonuniform cross section or compound open-channels. The governing equation is the one-dimensional momentum equation based on assumptions of the steady and uniform flow conditions in the longitudinal direction and the uniform water surface elevation in a cross section. Vegetative drag force term was included in governing equation in order to reflect the effect of floodplain vegetation on the flow characteristics. Finite element method was applied to obtain the numerical solution of the governing equation. Stage-discharge curve and lateral distribution of unit discharge for a given water surface are calculated based on input data, such as the cross sectional geometry, Manning's roughness coefficient, vegetative information and longitudinal slope of channel bed. The developed model was verified by comparing the calculated results with the observed data and the results of Darby and Thorne's(1996) model and the nonlinear k-$\epsilon$ model. The verified model was applied to estimate the upstream boundary conditions in two-dimensional flow model. The numerical results using laterally distributed unit discharge were compared with those obtained using uniformly distributed unit discharge in two-dimensional flow model.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.3
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• pp.149-158
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• 2015

In this study, we investigate tidal wave propagation characteristics, and classify regional tidal regime using tidal form number considered distribution of astronomical tide, overtides, and compound tides in the Han River Estuary, Gyeonggi Bay. The characteristics of the tidal wave propagation in main channels show dominance of major tidal constituents (e.g., $M_2$, $S_2$, $N_2$, $K_1$ and $O_1$) contributing to the astronomical tide however, distinct increasing of shallow water (e.g., $M_4$) and long period (e.g., $MS_f$) components toward up-estuary. Using the characteristics of tidal form number to astronomical tide, overtides, and compound tides, the regional tidal regime could be assorted into three regions. Firstly, a dominance area of astronomical tide was presented from open sea to a front of Incheon Harbor (Yeomha channel) and to north entrance of Seokmo channel. The area between south and north entrance of Yeomha channel and Ganghaw north channel classified into zone of showing strong shallow water components. It could be separated into upper estuary, upstream the Singok underwater dam, showed dominance of shallow overtides (e.g., $M_4$ and $MS_4$) water and long-term compound tides (e.g., $MS_f$) larger magnitude than astronomical tide. The shallow water components was earlier generated in lower part (south entrance) of Yeomha channel have strong bottom by effect of shallower and narrower compared with Seokmo channel. Tidal asymmetries of upper estuary cause by a development of overtides and compound tides are mainly controlled by influence of man-made structure.

• Journal of Korea Water Resources Association
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• v.48 no.4
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• pp.291-298
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• 2015

The aim of this study is that a theoretical formula for estimating the one-dimensional longitudinal dispersion coefficient is derived based on a transverse distribution equation for the depth averaged stream-wise velocity in open channel. In "Part I. Theoretical equation for stream-wise velocity" which is the former volume of this article, the velocity distribution equation is derived analytically based on the Shiono-Knight Model (SKM). And then incorporating the velocity distribution equation into a triple integral formula which was proposed by Fischer (1968), the one-dimensional longitudinal dispersion coefficient can be derived theoretically in "Part II. Longitudinal dispersion coefficient" which is the latter volume of this article. SKM has presented an analytical solution to the Navier-Stokes equation to describe the transverse variations, and originally been applied to straight and nearly straight compound channel. In order to use SKM in modeling non-prismatic and meandering channels, the shape of cross-section is regarded as a triangle in this study. The analytical solution for the velocity distribution is verified using Manning's equation and applied to velocity data measured at natural streams. Although the velocity equation developed in this study do not agree well with measured data case by case, the equation has a merit that the velocity distribution can be calculated only using geometric data including Manning's roughness coefficient without any measured velocity data.