植栽渠道流速分布與阻滯係數之研究

Velocity distribution and Retardance Coefficient in Vegetated Channels

高蘇白(Su-Pai, Kao)

指導教授 ： 陳彥璋

國立臺北科技大學/工程學院/工程科技研究所/博士(2009年)

https://doi.org/10.6841/NTUT.2009.00092

摘要

本研究主要目的有二，一為了解植栽渠道中流速分布特性，並提出新的植栽渠道流速分布理論；二為建立新的植栽渠道阻滯係數推估方法。流速分布是明渠流最為重要的課題之一，在植栽頂蓋上方的流速分布常利用對數流速分布理論，植栽頂蓋下方的流速分布則常用指數或冪流速分布理論。然而對數、指數和冪流速理論並不能完整的應用於植栽渠道流速分布。在本研究中提出一個基於機率論的植栽渠道流速分布理論。一系列的水生植栽渠道實驗也同時進行，以證實新提出植栽渠道流速分布理論的正確性。前人的研究大多針對陸生植物或利用人工塑膠條來模擬，僅有少部分的研究利用天然植物進行實驗。因此在本研究中，兩種不同的天然植栽被應用於估計阻滯係數的實驗中，研究中得知植物種類的不同會影響到阻滯係數。藉由分析實驗數據發現Froude number與阻滯係數具有指數關連性，Froude number是描述明渠流量流況的重要水理參數，並與河溪生物分布具有相關性，因此利用Froude number作為推估阻滯係數之用，可將水理參數及河溪生物分布相連接。

關鍵字

水生植物 ； 明渠流 ； 全浸沒條件 ； 植栽渠道 ； 流速分布 ； 福祿數 ； 阻滯係數.

並列摘要

The vegetation in channels results in loss of energy and retardance of water flow. However, this vegetation helps to stabilize the slopes and bottoms of open channels. Recently, vegetated channels have been used to improve the surface water quality and to reduce the delivery of sediment and nutrient to rivers and swales. Therefore, it is important to understand the velocity distribution of vegetated channels. The velocity distribution above canopy is usually assumed to follow the well accepted logarithmic law, whereas the velocity distribution below canopy is expressed by exponential law or power law. However, logarithmic, exponential and power laws can be affected by some characteristics of vegetation resulting in the sufficiently inaccurate description of velocity distributions in vegetated channels. In this study, and velocity distribution equation based on probability is developed to simulate the velocity distribution of vegetated channels in the submerged condition. An extensive series of laboratory experiments planted with Egeria densa Planch in the channel bed of the flume are carried out to devise and validate the velocity distribution equation. The results indicate that the developed model of velocity distribution have the applicability and capability to simulate the velocity distribution effected by aquatic vegetation.
The other important parameter of vegetated channel is retardance coefficient. Manning Equation is widely adopted to estimate open channel flows, and selecting retardance coefficient is always one of the most difficult task for estimating velocity and discharge. In cases of estimating accurate retardance coefficient values of vegetated channels, countless trial and error are to be made before reaching conclusive results due to conditions created by various aquatic plants. The majority of past studies on this subject, however, are established based on terrestrial plants and plastic moulds as laboratorial factors, and only few are done with natural aquatic vegetations. Hence, in this study, two different types of natural aquatic plants are applied to estimate retardance coefficients; and the result indicates that each type of plant affects differently in terms of flow resistance. Analysis of hydraulic parameters indicates there are strong correlations between the retardance coefficient and the Froude number. The Froude number is most important and commonly used parameter of open-channel hydraulics. The retardance coefficient and Froude number are exponentially related. Therefore, the Froude number can replaces the product of velocity and hydraulic radius (VR) to estimate the retardance coefficient, in which VR lacks a physical mean. Additionally, it can be used accurately to estimate velocity and discharge during river and wetland restoration.

並列關鍵字

Aquatic Plant ； Open Channel ； Submerged Condition ； Vegetated Channel ； Velocity Distribution ； Froude Number ； Retardance Coefficient

參考文獻

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