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題 名 | 河寬變化對辮狀河川型態演變之試驗研究=Experiments on the Adjustments of Braided River at Channel Width Variations |
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作 者 | 陳樹群; 安軒霈; 徐毅; | 書刊名 | 臺灣水利 |
卷 期 | 58:2=230 2010.06[民99.06] |
頁 次 | 頁49-70 |
分類號 | 443.6 |
關鍵詞 | 辮狀型河川; 渠槽試驗; 河工結構物; Braided river; Flume exeperiment; River training work; |
語 文 | 中文(Chinese) |
中文摘要 | 台灣地區河川中下游多為辮狀河型。辮狀型河川河寬較廣且河身順直,水流分叉,通常有兩股或兩股以上的叉道,輸砂量及粒徑均大。沿縱軸方向河谷比降較陡,橫向則主深槽有左右擺蕩的特性,寬深比較大,河川型態易改變,整體外型十分散亂。而在對辮狀河川的整治往往多以兩岸堤防為主,其目的在於對主流流路的束縮,使其受到控制以減少災害發生。然而在工程介入,改變來水來砂與河寬,辨狀河川隨即會展現自我調整的作用。本研究透過室內實驗,改變來水來砂與河寬,探討主深槽擺蕩、河床刷深和沙洲消長等河型自我調整現象。當實驗加砂停止後,上游段主深槽快速下切,中下游段因有上游來砂影響使主深槽下切轉為橫向擺蕩。同流量下,河寬漸寬時,主深槽形成時間漸慢,且沙洲數量增加,主深槽擺蕩週期漸大。同河寬下,流量漸大時,河道展寬與下切速率增加,主深槽擺蕩週期漸小。沙洲外型之長寬經無因次化後,有一固定關係,經與現地河寬沙洲資料比較,依然有此類似趨勢。最後發現,當上游有來砂的情況下,沙洲整體形態與輸砂量及流量有一固定關係,當輸砂量減少時,沙洲平均型態會較原來狹長。本研究歸納之演變特性,有助於辨狀河川整治之參考。 |
英文摘要 | Numerous rivers are braided morphology on the midstream and downstream in Taiwan. Braided river with large channel width and straight shape, and it usually has two or more branches. In longitudinal direction, braided river has rapid slope with fast flow velocity, plenty sediment discharge and larger particle size. In cross section, the mainstream shows swing character and the width-to-depth is larger, the area of sand bar is small but numerous. The shape of river could be changed so easily that it looks sprawl. The majority treatment of braided river is to build dike. It can contract mainstream and reduce the disasters. However, due to the construction, it changed flow discharge and sediment transportation from upstream and river width. Therefore, this study changed flow discharge and river width to simulate the adjustment of river morphology, then to discuss the issues of swinging mainstream, scouring river bed and growing sand bar. The experiment results, as sediment quitted, the mainstream of upstream degrade deeply and immediately. However, the midstream and downstream is effected by sediment from upstream and lateral bank erosion, so their mainstream change cutting into swinging. Under the same discharge, as the channel width increased, it takes longer time to form a mainstream and the mount of sand bar became increased, then the swinging cycle of mainstream increased. Under the same river width but flow discharge increased, the channel extension and rate of cutting will increase but the swinging cycle of mainstream gets shorter. As the experiment results compare with field data that the length and width of sand bar after dimensionless has a regular formula. It has the similar tendency in the experiment and field survey. In the experiment, we also found sand bar morphology has a regular relationship with sediment transportation and flow discharge. |
本系統中英文摘要資訊取自各篇刊載內容。