沖積河流深槽之安定與支配流量有密切關係。支配流量為滿岸水位附近之深槽流量。但深槽水位接近及超過滿岸水位後，將漫流於高灘地。對於植生茂密之高灘地，滿岸水位附近之水流將不足以浸沒高灘地植生。因植生糙率一般均大於深槽糙率，故需要探討高灘地植生對深槽流量的影響，以分析植生對於河流深槽安定與周邊環境保護的效果。
本文旨在以渠道部分寬度保持無植生，其餘寬度則佈置不同密度之植生條件下，經由理論分析及水工試驗，探討定量緩變速流流經未浸沒植生的情況下之流量分佈，以應用於研究沖積河流之支配流量。
由試驗結果可知，定量緩變速流由無植生渠道流入未浸沒之部分植生渠道時，因植生阻力之影響，主流區流量有沿渠明顯增加之變積流現象，但將漸趨穩定，臨近出口時才有流量漸減現象。由實驗觀察，植生密度愈大，主流區流量愈大，需要分析植生密度對主流區流量之影響。
由試驗結果亦可看出部分植生段之主流區與植生區之水位近似相等，橫向水面線可視為水平。
依據試驗結果，本研究假設部分植生段之橫向水面線水平，依據動量守恆原理推導植生區、主流區及全斷面之動量方程式。
因主流區與植生區之流速明顯不同，本研究依據流速實驗資料計算全斷面之動能修正係數及動量修正係數，並與以主流區平均流速及植生區平均流速計算之動能修正係數及動量修正係數比較，結果顯示二者頗為接近，故可應用主流區及植生區之平均流速計算動能及動量修正係數。
應用Moody chart求得渠道底床及岸壁之摩擦係數，則可依據實驗資料由全斷面之動量方程式分析植生圓柱之曳引力係數，其值介於0.6至1.2，平均可取為0.9；進而由主流區之動量方程式分析主流區與植生區間之無因次紊動混合長度比，其平方之值介於0.01至0.45，平均可取為0.23。上述分析結果將可應用於以主流區動量方程式及全斷面動量方程式以數值方法求解主流區流量及斷面平均水深。因數值方法較為繁複，本研究亦依據實驗資料，應用因次分析法獲得主流區流量 與全斷面流量 比值之經驗公式：
（4-13）
（4-13）式之計算值與實驗值之比較頗為一致，可應用於矩形斷面未浸沒之部分植生渠道之主流區流量推估。
由於部分植生對水流之阻力及束縮作用，未浸沒之部分植生渠道可能引起過度束縮而出現超臨界流，並因下游尾水之亞臨界流影響而出現水躍現象。
本研究推導未浸沒部分植生渠道之水躍判別式，可依據部分植生段之植生密度 ，植生寬度與全斷面寬度之比值 ，及沿渠福祿數 研判水躍之發生條件：
（2-32）
各組實驗之水躍現象觀察並與（2-32）式比較有良好之一致性，顯示（2-32）式為頗具實用性之水躍發生判別式。
由本研究之理論與實驗分析，顯示部分植生渠道可因植生密度之影響而增加主流區（無植生區）之流量，甚至發生超臨界流及水躍現象，故應用植生護岸時，應檢討是否會因增加主流區之流量而影響主流區底床之沖淤現象。由本研究之結果亦顯示對於沖積河流主深槽支配流量應視洪水平原之植生狀況進行分析。

There is a close relationship between the stability of main channel in alluvial river and the dominant discharge. Dominant discharge is defined as the main channel discharge nearby the bankfull stage. As the main channel stage is near or over the bankfull stage, the water will overflow into the floodplain. For the thick vegetated floodplain, the near-bankfull stage flow will not submerge the floodplain vegetation. Because vegetation roughness is always larger than main channel roughness, it is necessary to discuss the influence of floodplain vegetation on main channel discharge to analyze the effect of vegetation for main channel stability and surrounding environmental protection.
This research aims to maintain part of the width of the channel without vegetation while the other part lays out vegetation with different density. Meanwhile, to discuss the discharge distribution under the situation that steady gradually varied flow flows through emergent vegetation by theoretical analysis and laboratory experiment, in order to apply to investigate the dominant discharge of alluvial river.
From the experimental results, when steady gradually varied flow flows into the emergent partly vegetated open channel from non-vegetated open channel, because of the effect of the vegetation drag force, the main channel discharge increases significant along the flow direction but will be gradually constant. And then it decreases as it is getting close to the outlet. With the experimental observation, it is clear to see as the vegetative density increases, the main channel discharge increases as well. Therefore an analysis of the influence of vegetative density on main channel discharge is needed to be studied.
Based on the experimental results, the main channel stage is approximately equal to the vegetation stage in the vegetative reach. Hence the transverse water line is regarded as a horizontal line.
By the experimental results, an assumption of the transverse water line as a horizontal line was made in this research, which conducts the momentum equations of vegetation zone, main channel zone, and full cross-section according to the momentum conservation theorem.
Because the velocity between main channel and the vegetation are significant different, this research calculates the kinetic energy correction factor and the momentum correction factor according to the experimental velocity data, and then compares with the kinetic energy correction factor and the momentum correction factor calculated with the mean velocity of the vegetation zone and main channel zone. The results show each of them is approaching to each other. Therefore the mean velocity of the vegetation zone and main channel zone are accurate enough to calculate the kinetic energy and the momentum correction factor.
Applying Moody chart to obtain the friction factor of the channel bed and wall, and then using the momentum equation of full cross-section to analyze the drag force factor of the vegetation cylinder according to the experimental data. The value is between 0.6 and 1.2, the average value is 0.9. And then using the momentum equation of main channel zone to analyze the non-dimension turbulent mixing length ratio, the square of its value is between 0.01 and 0.45, the average is 0.23.
The aforementioned analysis results will be applied to the momentum equations of main channel zone and full cross-section to solve the main channel discharge and cross-section average depth by mathematical method. Because mathematical method is more complicated, based on the experimental data, this research uses dimension analysis method to obtain the experiential formula for the ratio that main channel discharge is divided by full cross-section discharge :
（4-13）
The value calculated by formula ( 4-13 ) is compared with the experimental value, and the result shows the agreement that it will be applied to estimate the main channel discharge of the emergent partly vegetated open channel with orthogonal cross-section.
Due to the drag force and the contraction that vegetations act on the water, the emergent partly vegetated open channel will cause the excessively contraction and the supercritical flow. At the same time, because of the subcritical flow downriver, it will also cause the hydraulic jump.
This research conducts the discriminant of the hydraulic jump of emergent partly vegetated open channel to distinguish the hydraulic jump according to the vegetative density of the partly vegetated reach , the ratio that the vegetated width is divided by the full cross-section width , and the Froude number :
（2-32）
The phenomenon of the hydraulic jump of each run in the experiment is compared with formula ( 2-32 ), the result shows the agreement that it is a practical discriminant of the hydraulic jump.
Based on the theory and experimental analysis in this research, it is obviously to see that the partly vegetated open channel will increase the main channel discharge because of the influence of the vegetative density, and even occur the supercritical flow and the hydraulic jump. Therefore applying vegetations to protect the bank should review whether the increasing of main channel discharge will affect the erosion and deposition of the main channel bed or not. Based on the results of this research, it also exhibits that the dominant discharge of main channel in alluvial river should be analyzed according to the vegetative condition of the floodplain.

1. 台灣地區河川區域植物圖鑑，經濟部水利署，民國93年6月。
2. 防洪工程設計手冊，台灣省水利局叢書之七十三號，台灣省水利局委託中國水利工程學會編印，民國58年6月。
3. 河川區域種植規定修正研究，經濟部水利署，民國93年6月。
4. 郭律君，「水流流經群樁之水理特性研究」，國立成功大學水利及海洋工程研究所碩士論文，民國94年6月。
5. 陳仁炯，「緩坡雨水下水道輸水能力之研究」，國立成功大學水利及海洋工程研究所碩士論文，民國95年5月。
6. 張乃薇，「植生渠床之定量緩變速流研究」，國立成功大學水利及海洋工程研究所碩士論文，民國95年5月。
7. Carollo, F. G. ; Ferro, V. ; and Termini, D., “Flow velocity measurements in vegetated channels.” J. Hydraulic Eng., 128(7), 664-673, 2002.
8. Chow, V.T., “Open-Channel Hydraulics.”, Mcgraw-Hill, 1959.
9. Elliott, A. H., “Settling of fine sediment in a channel with emergent vegetation.” J. Hydraulic Eng., 126(8), 570-577, 2000.
10. Forsell, B. ; and Hedestrm, B., “Lamella separation: A compact sedimentation technique.” J. Water Pollution Control Fedn., 47(4), 834-842, 1975.
11. Henderson, F. M., “Open Channel Flow”, Macmillan, 1966.
12. Juha Jrvel, “Flow resistance of flexible and stiff vegetation: a flume study with natural plant.” J. Hydrol. 269, 44-54, 2002.
13. Juha Jrvel, “Effect of submerged flexible vegetation on flow structure.” J. Hydrol. 307, 233-241, 2005.
14. Li, R. M. ; and Shen, H. W., “Effect of tall vegetations on flow and sediment.” J. Hydraulic Div., 99(HY5), 793-814, 1973.
15. Nepf, H. M., “Drag, turbulence, and diffusion in flow through emergent vegetation.” Water Resources Res., Vol. 35(2), 479-489, 1999.
16. Nepf, H. M., and Vivoni, E. R., “Drag and diffusivity within emergent vegetation.” Wetland Engineering River Restoration Conf., 1998.
17. Su Xiaohui and C. W. Li, “Large eddy simulation of free surface turbulent flow in partly vegetated open channels.” International Journal For Numerical Metheds In Fluids, 39, 919-937, 2002.
18. Stone, B. M., Shen, H. T., “Hydraulic resistance of flow in channels with cylindrical roughness.” J. Hydraulic Eng. 128(5), 500-506, 2002.
19. Tsujimoto, T., and Kitamura, T., “Velocity profile of flow in vegetated-bed channels” KHL Progressive Rep. No. 1, Kanazawa University, Japan, 1990.
20. Tsujimoto, T.,”Fluvial processes in streams with vegetation.” J. Hydraulic Res. 37(6), 789-803, 1999.