- 期刊
- OpenAccess
防砂壩下游天然河床受壩頂溢流沖刷之研究
Study on the Scour Below a Sabo-dam Caused by Crest Overflow
摘要
本研究以自由冲射流理論建立防砂壩下游天然河床局部冲刷之沖刷深度變化規律。研究結果顯示，壩下游河床泥砂顆粒起冲後，其最大冲刷深度爲受相對速度及冲刷福祿數（scouring Froude number）所影響。經理論與試驗分析獲得下式：h_d+h_s/h_u=0.91(U/U_c)^(1.5)√1+2/Fr^2。利用此式引用不同研究者之冲刷試驗資料以預測可能之最大冲刷深度，亦獲致良好之結果。本研究並採用因次分析法，分析壩下游河床泥砂顆粒之消能效率，證實天然河床確有消能之良好效果。如壩底滲流影響可予以排除，則使用天然河床替代混凝土護坦以克服溢頂水流之沖擊，不失爲較經濟之對策。
並列摘要
The research presented herein is concerning the variation of the scour depth in the natural channel bed below a sabo-dam. The foundation of the theoretical analysis is the free plunging jet theory. The results show that the maximum scour depth is determined by the relative velocity and the scouring Froude number, once the sediment of the channel is on the incipient stage of movement. Both theoretical and experimental analysis give the following formula: h_d+h_s/h_u=0.91(U/U_c)^(1.5)√1+2/Fr^2. Applying this formula to estimate the maximum scour depth with other researchers' experimental data, good results are achieved. In this paper, an analysis upon the efficiency of energy dissipation of the river sediment is also made. It is based on dimensional analysis and has proved the natural channel bed itself is a good agent of energy dissipation. If the influence of seepage under the base of the dam can be made less, the use of the natural channel bed as a substitute for concrete apron can be justified.