台灣位於環太平洋地震帶，地震發生相當頻繁，因此易使土壤鬆軟，加上氣候變遷導致極端降雨事件發生機率增加，每逢雨季時上游產生大量泥砂進入水庫，造成庫區嚴重淤積，影響到水庫的使用年限，為維持水庫能永續經營，許多水庫正透過各種方法實施水庫排砂。
水庫進行排砂操作後，將使大量的泥砂由庫區進入至水庫下游河道，導致河川下游型態改變，進一步影響到生態、防洪等安全。
本研究選取阿公店水庫下游及南化水庫下游作為研究區域，藉由現場調查及資料蒐集(斷面地形及粒徑分析)，以評估排砂操作對下游河川河相之影響。根據河道沖淤量變化量可知排砂操作後，阿公店溪排放之泥砂大多數皆可輸送至距離水庫放流口下游4,436 m處以下；南化水庫模擬以及兩次的地形資料顯示，整體下游河道泥砂運輸能力強，模擬排砂操作後下游河川僅產生少量的淤積，對於興建水庫後下游缺少泥砂來源有補給的功用。由本研究之細粒料填縫分析可知，在沒有防淤隧道操作的情況下，河道本身能透過大流量的攜帶能力改善細粒料填縫情形。
水庫的興建導致水庫下游河川長時間泥砂缺少補給，造成下游河道沖刷，因此藉由水庫的排砂操作，對下游河相將會有泥砂補給的功用，就整體而言，水庫排砂操作對於下游河相的影響，由泥砂的角度來看，是有益的。

Part of the Circum-Pacific Seismic Zone, Taiwan has been frequently struck by earthquakes that lead to soft soil. As extreme rainfall caused by climate change is increasing, a large volume of sediment from upstream flows into reservoirs in every rainy season followed by severe deposition which affects the useful life of reservoirs. To keep reservoirs sustainable, methods are carried out in many reservoirs for desilting.
After desilting, a large volume of sediment flows from reservoirs to downstream that changes the downstream morphology and influences ecological safety and flood control.
Taking the downstream of Agongdian Reservoir and Nanhua Reservoir as the studied area, the study through field survey and data collection (section topography and particle size analysis) evaluates the effect of desilting on the downstream morphology. According to the scouring and silting variation, it is known that, upon desilting, the bulk of sediment released from Agongdian River can be transported to the downstream at 4,436 m from the reservoir effluent. Nanhua Reservoir simulation and two topographic data demonstrate a great sediment transport in the downstream way. With simulation of sediment releasing, only a small volume of sediment in the downstream river occurs as a complement to a shortage of sediment in the downstream after reservoir is built. It is known from an analysis of the fine sediment infiltration that, without desilting tunnel, the watercourse itself with great carrying capacity improves the fine sediment infiltration.
Building reservoir causes long shortage of sediment and channel erosion in the downstream river, so sediment released from reservoir is a complement to the downstream morphology. Generally, reservoir desilting has beneficial effect on the downstream morphology, in terms of sediment.

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