本文就自由跌流之跌流工邊緣水深(Jb )、下游沖擊位置(Ld)及下游 尾水深的)等水力參數，先採用6組既有渠槽試驗之結果，進行CCHE2D 之數值模擬跌流工流場。藉由比較兩者結果之差異，以及檢定誤差屬可信 賴區間，獲致驗證數值模擬之可行性。進而再以CCHE2D模擬跌流工上、 下游渠床坡度同時變化(Su、Sd= 2、4及6%)，構成9種不同試驗條件之組 合，以預測上游正常水深(Y。）、跌流工邊緣水深(Yb)、下游沖擊位置{Ld)及 下游尾水深朽)之結果。研究結果獲致本CCHE2D數模，可提供相關自由 跌流工未來物理試驗之應用。

This study carries out the numerical simulation of free overfall flow field using CCHE2D. Six existing channel testing results are adopted for comparison with various free overfall brink depth of water (Yb), downstream impact position (Ld), and tail depth of water (Yi). Through the comparison between numerical simulation and testing results, and examination of reliable range for error, the numerical simulation is verified for further application. Then, the CCHE2D is used to simulate the upstream and downstream slopes Su , Sd(0,2,4,and6%), and nine series of objects are assembled. The normal upstream depth of water (Y0), brink depth of water (Yb), downstream impact position (Ld) and tail depth of water (Y1) can be evaluated. The analyzed results above can be provided in the application of physical test of drop structure.