礫石河道的沖蝕試驗之研究－－以火炎山礫石沖積物為例

Experiment on fluvial processes of conglomerate channel - an example of Hoyenshan conglomerate sediments

本研究以瞭解礫石河床的推移質搬運方式與坡度的關係，並用以探討火炎山沖蝕溝可能的沖蝕與搬運方式。研究對象為三義火炎山的礫石沖積物，利用柏林自由大學水文地形實驗室，模擬豪雨時的水文現象，探討不同坡度的沖蝕與搬運特性。實驗結果顯示在平緩的河床上（小於4°），推移質的搬運量並不多。然而豪雨時河川流速超過每秒鐘2公尺的流速時，礫石便很容易被搬運，顯示流速高的水流對礫石搬運的搬運能力非常強，而坡度超過7°（15％）以上的礫石河道，非常容易被流速2－2.5公尺的急流搬運。實驗槽中的火炎山礫石，如果沒有特殊的阻礙物，非常容易被搬運離開原來的位置，在10分鐘之內，實驗槽中的礫石便全數被搬運殆盡。本研究顯示礫石在河道中搬運河床坡度有關連性。

This study mainly focuses on the experiment of fluvial process on conglomerate channels. The sample comes from our research area, Hoyenshan, mid-western Taiwan. The main purpose is to understand the relationship between the delivery of conglomerate pebbles as bed load and the gradient of the channel. The flume experiment has been carried out at the Freie University, Berlin, Germany. For the experiment, the main factors involved are the flow speed and gradient of channel and we control the flow speed and make the gradient as the only variable in the experiment. The characteristics of the transportation of bed load are then being discussed. The results show that the bed load is not transported too much on gentle channel under the inclination less than 4 degree. However, the sediments will be removed dramatically when the gradient of channel higher than 4 degree. If the gradient is over 7 degree, or 15%, the bed loads will be transported within 10 minutes at the flow speed between 2 to 2.5 m/sec. The results also demonstrate the power of the fluvial processes and the relationships between channel gradient and bed load transportation.