Steady gradually varied flow in vegetated channels

• Main Authors: Nai-Wei Jhang, 張乃薇
• Other Authors: Chang-Tai Tsai
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/44593951708313982953

碩士 === 國立成功大學 === 水利及海洋工程學系碩博士班 === 94 === The vegetation in the floodplain and along the bank can increase roughness of the ground, retard the flow velocity, and bear some shear force. Hence, it can prevent bed erosion and enhance bank stability. However, the water stage was rise and conveyance of flow was retard due to decrease of wetted cross-sectional area. In recent years, the hydraulic phenomenon about flow resistance for the vegetation is more and more important cause of the ecological engineering methods were used. The purpose of this study was to investigate the effect of vegetation, that include the interrelation between both the flow above and through the vegetation and the vegetation densities, in steady gradually varied flow by laboratory experiment and theoretical analysis. The cylinders were used to simulate the stems of vegetation because of their shapes are similar. The exchange of momentum between the flow above and through the vegetation, and the hydraulic resistance were analyzed by the one-dimensional steady gradually varied flow. Equations derived based on the conservation of mass and momentum may be expressed as : Continuity equation: Momentum equation: The formula of dimensionless turbulent length ratio can be mathematically described in turbulent shear stress on the interface between upper and lower level. The formula was useful for calculating the discharge of the upper and lower level. The results indicated that the influence of the resistance coefficient by submerged cylinders on cylinder densities, submergence ratio, and cylinder Reynolds number. Therefore, the condition with the same submergence ratio in the channel, the dense cylinders decrease in both the resistance coefficient and the flow velocity and increase in water stage when the flow through the submerged dense cylinders. In this study, the one-dimensional numerical model was developed by the finite difference scheme was applied to discrete the governing equations that was steady gradually-varied flow in the vegetated channel and proved by laboratory experiment. The numerical model was applied to simulate the flow depth and discharge in the emergent and submerged vegetated channels well. The results of experiment and simulation indicated that the flow discharge was changed both above and through the vegetation and along the direction of flow. According to the results that were increase in the understanding to the phenomenon of flow through vegetation and application of reality. Moreover, the influence of flow on the difference vegetation density was simulated by model. Keywords：vegetation；steady gradually varied flow；resistance coefficient