台灣灌溉水源多自河川修築矮堰取水；多數導水堰為臨時性土石堰。本研究為探討臨時性土石攔河堰因河川逕流改變而破壞之原因，並以台灣中部3條河川9處之渠首工臨時攔河堰為研究對象，進行渠首工臨時攔河堰之安全性分析，其次以丁壩之安全性分析依臨時攔河堰尺寸分析土石堰破壞之流速臨界點。本文探討沖毀臨時攔河堰之流速臨界點為2.10～4.34 m/s；影響破壞臨界點流速之因素為攔河堰與河川水流夾角，本研究建議改善方式為渠首工臨時攔河堰軸線與河岸應縮小角度設置。其次本文以MODFLOW模式模擬評估滲流對臨時攔河堰的破壞影響，並針對4種改善措施進行比較，以減緩堰體滲流速度而言，改善方法優劣依序為加強夯實、堰體加寬2倍、堰體加寬1.5倍、堰體上游坡面施設防水布。
Most irrigation water in Taiwan is collected from rivers by using temporary low embankment dams, which are mostly made of riverbed soil and rock. This study is to investigate the causes for damage on the temporary embankment dams due to runoff change of the rivers. The 9 temporary embankment dams constructed for irrigation of three important rivers in the central Taiwan are adopted as the research objects. Safety analysis of the temporary embankment dams of the canal headwork is carried out. Moreover, the critical flow velocity point for the destruction is calculated by using the safety analysis procedures of spur dikes. This study investigates critical flow velocity causing the destruction of the temporary embankment dams is about 2.10-4.34 m/s. Moreover, the factor that affects critical point of the flow velocity of destruction is the angle between the embankment dam and the river flow. Therefore, the proposed improvement suggestion in this study is that a small angle between the axis of the temporary embankment dam for the canal headwork and the river bank over waterway area should be adopted. Secondly, the MODFLOW model is adopted to simulate and evaluate the impact of seepage flow on the destruction of temporary embankment dams, and four types of improvement measures are proposed and compared. In terms of slowing down the seepage velocity of the temporary embankment dams, the improvement methods in order are to strengthen compaction, widen the dams by 2 times, widen the dams by 1.5 times, and install waterproof cloth on the upstream slope of the dams.
