柳枝工抗掃流力特性及其對魚類避難效應研究

Study on Hydraulic Resistance Characteristics and Fish Shelter Effect Evaluation of the Willow Works

黃勝頂(Shen-Ting Huang)

中原大學/工學院/土木工程研究所/博士(2011年)

https://doi.org/10.6840/CYCU.2011.00059

摘要

近年來因為人類對於土地的利用大幅擴大，造成許多動物與植物的生存空間受到災害；而這些衝擊的累積也導致大自然的失調與反撲。而生態工程正是人類思考並研究如何結合硬體上的工程與生物自我回復能力的方法，進而改善人類對大自然開發所引起的災害之減災措施。以溪流環境為例，其本身除了自成一完整的生態系統，更是居住在水中所有生物不可或缺的維生體系，有關生態工程的應用範圍，也同時涵蓋了水利工程之親水護岸與河川復育等功能。以往水利工程以加強水工構造物安全穩定的目標思維，將有所轉變。也就是要如何在安全無虞之情況下，恢復河川原有動態生命力，將是今後水利工程師在設計上必須重新思考的方式。柳枝工，係古中國水利工程中主要是用來做坡面保護及防止沖刷等功能之重要防洪方法。因為其富有相當大的生態意涵，在2004年政府與民間推動生態工程的風潮下，從日本第一次引進到台東卑南溪做為試辦工程。由於該工法在工學的計算上以及水理特性的研究上仍然相當缺乏，因此本研究透由水工模型的試驗，來釐清當水流流經以竹枝插入石頭編柵中擬似柳枝插枝狀態下之水理特性，並藉此獲得其粗糙係數之重要參數。同時在案例分析中，由現地所觀測到莫拉克颱風洪水量在柳枝工場址中的水位高度及附近之河川局水文觀測站之資訊，校正模擬場址之河床粗糙係數。同時將兩者的參數值應用在模擬的柳枝工護岸中，進一步探討其近岸流速與生物可避難棲地之分析。
室內水工試驗結果顯示，模擬現地柳枝工之曼寧係數大約介於0.132～0.133之間，該結果與Chow (1959)、Subramanya (1992)所推估出來的柳枝護岸相似。當柳枝工模型高度為0~11公分時，進行迴歸分析後，得到其拖曳係數Cd與曼寧係數n值的關係式為 ；當柳枝工模型密度為0～1之間，進行迴歸分析時，得到其拖曳係數Cd與曼寧係數n值的關係式為 。實驗的結果可提供做為使用柳枝工護岸施工時規劃設計之參考。在案例分析中，透過校正的過程將原有河川局所建議之該河段曼寧係數0.038修正為0.040；並且利用日本護岸力學的計算方式，演算出該模擬河段使用的塊石大小不足的問題。接著，將水工試驗所推估之柳枝工粗糙係數與水位校正後之河床粗糙係數應用在二維的數值模擬上。模擬結果顯示，利用混凝土護岸與柳枝工護岸之接近流速比較出其減少率為29.85 %, 43.02 %以及60.52 % 分別所對應之流量是Q10, Q20以及 Q50，初步顯示出柳枝工護岸可以有效降低流速進而減少河岸沖刷的問題。另外本研究利用高流量的條件下，透過WUA(生物可利用棲息地面積)的顯示與比較，證明出柳枝工之生態性量化的指數。該模擬結果顯示，WUA值分別在流量為Q10, Q20以及Q50中，柳枝工護岸與混凝土護岸之差異值為3,374.18 m2, 1,617.9 m2以及6,749.01 m2。該結果表示在高流量情況下，柳枝工在保護台灣石賓(卑南溪特有種)能力較混凝土護岸來得高。因此，本研究最主要的貢獻與價值在於以科學的方法來提出對於這項古水利工程之安全性與生態性提出證明；並且完整提供一個研究柳枝工水理特性的方法、流程與步驟做為未來在探究柳枝工完整力學機制之先期研究。有關柳枝工之根系所產生的臨界拖曳力之保護護岸機制，有待後人深入探究，建議未來可以將兩者之研究結果結合，成為完整柳枝工之抗掃流與生物力學保護機制之建立，成為該水利工法之規劃設計之方針與手冊，使其廣泛使用，以作為工程師在相關護岸工法設計施工時之參考。

關鍵字

柳枝工 ； 水工模型 ； 數值模擬 ； 曼寧係數 ； 幾何高度 ； 拖曳係數 ； 掃流力

並列摘要

Recently, human activities have contributed to changes in the surrounding area. These activities cause the expanses of land usage and also damage the habitat for aquatic and terrestrial plants and animals. Besides, the shortage of renewable resources and global pollution make the variety of species reduce and environments lose their order. If these impacts on nature can not be controlled or reduced effectively, the results will influence the humans’ living and life directly. However, ecological engineering is one of the best ways for human beings to reconstruct and to rebuild the destroyed ecosystem. As an example of water environment, river and stream corridors are complex ecosystems. They perform a number of ecological functions and provide habitat for aquatic creatures. Therefore, hydraulics and constructions shall be carried out that compromise between flood defense and ecological interests by introducing appropriate rehabilitation methods in the application of ecological engineering. Besides, hydraulic engineering must consider the benefit of both in human society and riparian ecosystem restoration. In other words, the former designing and planning target of river engineering will switch from passive flood prevention that involves enhancement consideration of the hydraulic structure into active restoration that involves intervention and installation of methods to repair damages to the structure of stream corridors. The willow works, an ancient Chinese traditional method applied in riverbank protection. It fits in with the concepts of ecological engineering, i.e. natural materials utilization, flood prevention and ecosystem habitat creations. Unfortunately, because of the development of concrete material, this method did not carry out for many decades in Taiwan. In 2004, 485m length willow works as the attempted constructions were first achieved in Beinan River, Taitung. The construct techniques were introduced by some Japanese engineers. In the aspect of hydraulic engineering, the first contribution of this research is to quantify the flow retarding effects of the willow works from the flume experiments. In the case study, through the observations of the flood water level and the hydrological information data of local river management office, the river bed roughness calibration jobs were conducted. This study utilized both the flume and calibration results into the 2D model simulation to analyze the approach velocity and aquatic creature shelter effect in the true flow field.

The experimental results showed that for the Manning’s n of the willow works is between 0.132~0.133 which corresponding height to the real field is about 144cm to 176cm. They were very similar to the proposed results by Chow (1959) and Subramanya (1992). Through the regression analysis, the relationship between drag coefficient Cd and Manning’s n is while the heights of the willow model is 0~11cm; through the regression analysis in results of various densities between 0~1, the relationship between Cd and n is . These results can be utilized in planning and designing the willow works. In the case study results, the river bed roughness is modified from 0.038 to 0.040 due to the calibration from the Typhoon Morakot flood event. However, the problem of stone size was also highlighted through the Japanese pavement safety estimation method. Fulfilling previous two main steps in experiment and model calibration, the approach reduction rates are obtaining as following, 29.85 %, 43.02 % and 60.52 % corresponding to the discharge of Q10, Q20 and Q50, respectively. Those results indicated initially that the willow works revetment can effectively reduce the flow erosion problem. Then, this study presented that the WUA differences between the willow works and concrete materials were 3,374.18 m2, 1,617.9 m2and 6,749.01 m2, corresponding to the discharge of Q10, Q20 and Q50, respectively. These results summed up as the willow works provided more habitats for Acrossocheilus paradoxus (special species in Beinan River) than concrete revetment in flood season. Therefore, the primary contributions and values of this research are to provide the evidence of safety and ecology to this ancient hydraulic construction method with modern scientific ways; to give a complete studying methodology to the hydraulic characteristics of the willow works; and to fulfill the previous research in establishing the whole mechanism of the willow works. Especially the root reinforcement part of the willow works, it needs the future research to realize the critical drag force. Combining two major results into one whole mechanisms which is including flow resistance and biological issues, the guideline and manual of this hydraulic engineering method-the willow works could be performed.

並列關鍵字

Willow Works ； Drag coefficient ； Geometric Height ； Manning’s roughness ； Numerical Model ； Hydraulic Resistance ； Flume Study

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