| Summary: | 博士 === 中原大學 === 土木工程研究所 === 99 === 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.
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