本文主要在探討圓形渠道中單柱與雙柱橋墩沖刷的特性，並與直線渠道做比較，利用實驗所得到的結果來做分析討論。
本實驗在單柱沖刷中，隨著橋墩擺設離內岸的位置遠近，沖刷深度也隨之改變，在扣除離內岸10公分與50公分受邊壁及束縮效應的影響，大體上可以得到愈靠近內岸沖刷越明顯的趨勢，沖刷坑呈現出左右不對稱，沖刷坑範圍靠外岸處比靠內岸處範圍大，其後方的沙丘發展偏向內岸發展。
在雙柱沖刷試驗中，雙柱之前柱的沖刷型態大體上與單柱沖刷相似，兩者沖刷歷程亦頗為相似，而其平衡時間則較單柱時快，黃等（1999）及Hannah（1978）之結果比較，發現之間的沖刷歷程也為相似，平衡時間比直線渠道較快。在後柱方面，因受到前柱的遮蔽效應，或前柱產生之沙丘影響，產生的沖刷歷線與單柱時差異頗大，僅在α=3.5時，其結果與單柱時結果相近，由於後柱在不同柱距的沖刷歷程差異很大，存在變因很多，不便與直線渠道做比較。

This paper is to explore the characteristic of single pier and double piers in the circular channel and to compare with the straight channel. Using the result of the experiment to analyze and discussion.
This experiment is that scouring in single pier with the set of the pier and locate from inner bank lets the scour depth change. Deducting from 10cm away from inner bank and 50cm boundary and contraction effect we broadly can get: The trends of the more are far away from the inner bank the more scouring. The unsymmetry of scour hole arises up. Scour hole range of outer bank is bigger than inner one. Behind sand hill develops to be partial to inner sank.

In the double-piers scour experiment, we find: The scour is similar from single-pier to front one of double-piers. The balance time is more fast than single-pier.
Comparing with result of Huang (1999) and Hannah(1978) we find scouring processes among us are similar and balance time is faster than straight channel. In the side of behind pier, because it is effected by front pier shield effect or sand hill produced from front pier. It makes scour hydrograph much different to single pier. Only at α=3.5 ,the result is similar single-pier. Because behind pier form different scouring processes has large difference and many variables. Let it is not easy to compare to straight channel.

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