常流量下固床工下游形成沖刷坑之初步實驗：玉桂嶺野溪案例

Preliminary experiment on the scour hole of grade-control structure: case study of Yu-Kua-Lin stream

陳晉琪(J.-C. Chen) ； 蕭宇吟(Y.-Y. Hsiao)

《華梵藝術與設計學報》 10期 (2015/07) Pp. 15-29

摘要

本文以新北市石碇區玉桂嶺南勢坑野溪中的固床工為研究對象，在常流量條件下進行固床工下游形成沖刷坑之實驗，希望藉由實驗了解影響沖刷坑位置與大小的因素，以及探討現有河床質及固床工下游拋石大小的穩定性。首先，利用模型相似原理(滿足幾何相似及動力相似)，決定玉桂嶺南勢坑野溪中固床工之模型尺寸，並決定實驗分析時之常流量。其次，以兩組不同粒徑為材料，進行室內水槽試驗。細粒料部份，主要分析固床工上游河床高度及流量的變化，對沖刷坑形成位置與形狀的影響。粗粒料部份，探討現有固床工下游拋石大小的穩定性。最後，討論塊石的穩定條件及沖刷坑的變化與現地環境的關係。研究結果顯示，當固床工上游河床高度H1 與流量Q 較大時，沖刷坑形成的位置會離固床工越遠，並且當H1 或Q 增加時，形成沖刷坑之深度會有加深的趨勢。此外，就單以現地河床細粒料(＜15cm)來看，其雖有助於沖刷坑的發展，但亦會造成固床工基礎的破壞；目前拋放於固床工下的大塊石，就常流量下雖可保護固床工基礎，但過量的拋放，恐不利於沖刷坑的形成並危及魚類的棲地。

關鍵字

固床工 ； 相似原理 ； 沖刷坑

並列摘要

The Yu-Kua-Lin mountainous stream located in Shihding district, New Taipei city is selected to analyze the scour hole of grade-control structure through flume experiment. The stability of the riprap size downstream the grade-control structure was also discussed in this study. Firstly, the model size of the grade-control structure, and the flow dischrage and the sediment size required in experiment were determined by using the principle of similarity (the geometric similarity and dynamic similarity). Two sediment sizes, the fine sediment with diameter of 0.6 - 0.83cm served as gully bed and the coarse sediment with diameter of 1.5 - 2.5cm served as riprap, were used in the experiment. Secondly, the variation of scour hole caused by water flow over the grade-control structure was measured at various heights of gully bed upstream the structure. Finally, the stability of the size of riprap downstream of the grade-control structure was investigated. The experimental results showed that the depth of the scour hole will be deeper when the height of gully bed upstream the structure is higher or when the inflow discharge is greater. Preliminary study results also showed that the protection of the riprap size downstream the grade-control structure will be stable under general flow in the case of the Yu-Kua-Lin stream.

並列關鍵字

grade-control structure ； principle of similarity ； scour hole