中文摘要
為保護堰壩閘門之安全穩定，於下游常設置護坦保護工。但由於護坦末端易因多次水流刷深後產生基礎裸露，因此加置尾檻挑流設計。藉此改變出口水流條件，使高速水流挑離基礎處，於較下游處落入尾水，達到削減能量及轉沖為淤之保護功效。本研究為清水沖刷試驗，研究重點在於尾檻迎水角度與高度之變化，分別探討並比較無尾檻條件、矩形尾檻及梯形尾檻挑流保護工等三種不同試驗模型，於深、淺尾水流況下之水流型態及沖刷機制。應用理論分析配合實驗結果，試圖找出沖刷坑特徵尺度(最大沖刷深度，最大刷深位置，基礎刷深等)之間相互關係，可供推估各流況條件下尾檻下游之沖刷坑型態。最後並相互比較，期望能瞭解尾檻變化所造成之影響，以提供最佳之尾檻設計角度做為工程參考之依據，達到防沖消能保護功效。
研究分析結果得知，當比較相關沖刷坑特徵尺度，發現在迎水30°比另外15°、45°及90°三種角度防沖效果為佳，且30°對於各類尾水適應性較佳，因此研究建議以梯形30°作為尾檻保護設計角度。

Abstract
In order to protect the dams or weirs, many energy dissipaters such as apron, sills to aid in energy dissipation or to deflect high velocity flow away from the channel bed. This study examine the effect of angle of sills and the tailwater depth related to the scour mechanism. The characteristics of the scour profile shows strong dependence on the tailwater depth..
There are three series of experiments in this study : the plane wall jet (no sills)，the wall jet with a rectangle sill , and the wall jet with a trapezoid sill. The experiments were preformed with clear water and homogeneous sand beds.
According to experimental data, the trapezoid sill with the angle of
30°is the best design for protection of the downstream riverbed near those structures, and this angle is proposed for the design of the sills.

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