高灘地上植生增加地表糙度，遲滯水流之流速，並承受部分水流剪力，因而可減少河岸土壤淘刷，有固土護岸的功能。不過，也減少渠道之通水面積，使得水位抬昇，遲緩洪水宣洩。近年來，由於生態工法的推動，更日益重視河道植生相關研究。
本文目的以不同密度及高度之剛性圓柱樁模擬植生莖幹，經由理論分析及水工試驗，探討定量緩變速流下，上層水流及植物莖間水流與植物密度的關係。基於一維定量緩變速流的理論分析浸沒植物莖間水流與植物上方水流動量交換情形，以及植物莖幹之流動阻抗，可得一維定量緩變速流下浸沒植生渠道之基本方程式：
連續方程式：
動量方程式：

本研究亦推導上層與下層交界處有關紊流剪應力的無因次紊動長度比公式，應用於上層與下層動量方程式，顯示具有良好之可靠性。
由理論分析及試驗結果可知，浸沒圓柱群樁之阻力係數受圓柱密度、相對浸沒深度及圓柱雷諾數影響而變化；因此，在渠道中同樣浸沒深度之浸沒植叢越茂密，其植叢阻力係數越小，且當植生越密，植物莖間流速越緩，水位抬昇越高。
本研究以有限差分法求解基本方程式而建立植生渠道一維定量緩變速流演算模式，並以試驗結果驗證，顯示對於浸沒與未浸沒混合之植生渠道之沿河水深及植生上下層流量變化具有良好的模擬能力。由試驗及演算結果可看出，浸沒植生渠道，上層（無植生層）與下層（植生層）間可有流量交換，沿河上層及下層流量均有沿流向改變之現象。此結果增進對水流流經植生渠床之特性的了解，並且可由模式演算得知不同植生密度對水流流況之影響，以增加實務上之應用。

關鍵字：植生；定量緩變速流；阻力係數

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

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