| 摘要: | 早期台灣河川整治，常在河川設置水工結構物以達成防洪和河道斷面穩定之目的，卻忽略對魚群棲地等影響。本研究探討丁壩設置後，評估生態棲地影響範圍之消長，討論丁壩工設置對原始河道魚群棲地之影響。 本研究選用台中筏子溪為例，台灣石?為標的魚種；結合一維水理模式HEC-RAS和河川棲地二維模式River 2D進行模擬，以5%WUA(權重棲地可使用面積Weighted Usable Area)增減率判定筏子溪丁壩影響範圍，結合近十年台灣地區丁壩相關文獻，探討丁壩對魚群棲地之影響範圍，以及丁壩建置要素如河寬、壩高、壩長(阻水率)、流量、河道平均坡降、單雙丁壩工以及丁壩群等對其範圍之影響。 研究結果顯示，不論丁壩阻水率為何，對下游之影響範圍皆遠於上游之範圍。丁壩設置後上游影響範圍最遠可達2.5L，下游影響範圍最遠可達9L(L為無因次丁壩長度：影響範圍)。河寬部分以River 2D模擬筏子溪為例，當河寬比超過最低有效河寬比85%(流量為40cms)，丁壩方可在河道中碰觸水流並發揮其功能。在相同河道上，上下游影響範圍比會隨壩長(阻水率)和壩高的增加而上升，卻會隨著坡降以及流量的增加而下降。但當流量趨近至十年重現期距時，其上下游影響範圍比將會趨於一定值2。設置雙丁壩之方式，對魚群生態棲地會比單丁壩有較佳的影響。在阻水率為1/10時，單丁壩有較高的上下游影響範圍比但阻水率為1/6時，丁壩群且間距為1.5倍壩長時有較高的上下游影響範圍比。丁壩群之壩高越高，會有較高的上下游影響範圍比。 In early times, river engineered construction in Taiwan concentrated only on the stability and flood control of a river, while ignoring the influences on environment and habitats of fish. This research discusses the influence on the living creature’s habitats area after the building of a spur dike. Fazih River was chosen as the study area and the acrossocheilus paradoxus as the target fish species. HEC-RAS and River2D are combined to investigate the influenced area of spur dike, and 5% change of WUA (Weighted Usable Area) is set as the threshold to define the spur dike’s influenced area. Furthermore, the references of spur dike in the recent 10 years published in Taiwan are reviewed and analyzed with respect to variant factors for construction of spur dike, such as the width of channel, height or length of the dike, elevation, group of spur dikes and flow discharge. The result shows that in spite of the length of the dike, the influenced area downstream is farther than the influenced area upstream. After building a spur dike, the farthest influenced area upstream can reach up to 2.5L, while the farthest influenced area downstream can reach up to 9L(L means the Dimensionless influenced area). Taking the Fazih River as a simulation, when the ratio of spur dike and width of channel (the length of spur dike / the width of channel ) is over 85%(discharge is 40 cm), spur dike is able to reach the water and take effect on the river. In the same channel, the ratio of influenced area (downstream/ upstream) will increase while the length and height of spur dike are increasing, but will decrease while elevation and discharge are increasing. When the discharge is approximate to 10 years return periods, the ratio of influenced area will be close to a constant value 2. Building double spur dikes for simulation will produce a better WUA than building single spur dike. When the ratio (Length of dike / Length of channel) is 1/10, single spur dike will produce a higher ratio of influenced area than the group of spur dikes. When the ratio (Length of dike / Length of channel) is 1/6, and the distances between the group of spur dikes are 1.5 times as the length of spur dike, we will get a higher ratio of influenced area. The result also shows that when the heights of the group of spur dikes are higher than the elevation of water surface, it will also produce a higher ratio of influenced area. |
