高雄市海軍左營第二港口擴建工程因涉及後勁溪下游河道改道與出海口位置調整，可能改變整體流域排水條件及淹水情形。本研究以後勁溪流域為研究範圍，探討港口開發前後對區域淹水潛勢之影響，並評估不同降雨條件下的防洪效益。
本研究採用D-Flow Flexible Mesh (D-Flow FM) 1D-2D耦合數值模型，建立開港前與開港後兩套數值模型，並以2024年凱米颱風事件進行分析，以確認模式之可靠性，研究範圍涵蓋後勁溪集水區及周邊都市地區，模擬多種降雨量及不同重現期情境，分析開港前後之淹水面積、水位變化及空間分布差異。
研究結果顯示，港口開發後因河道縮短及排洪路徑改變，整體排水效率有所提升，多數情境下淹水面積均較開港前減少。在降雨量較低的情境下，減災效果最為明顯，例如6小時累積降雨150毫米時，淹水面積由153.82公頃降至64.84公頃，減少88.98公頃，降幅達58%。在極端降雨情境下，雖然減少比例下降，但減少的實際淹水面積仍相當可觀，例如24小時累積降雨650毫米時，淹水面積由1107.90公頃降至754.84公頃，減少353.06公頃。整體而言，開港後情境均呈現淹水範圍縮減及排洪能力提升的趨勢。
依據模擬結果，左營第二港口擴建工程並未增加後勁溪流域整體淹水風險，更因改善河口排水條件而降低多數區域的淹水潛勢，然而，在極端降雨事件下，流域仍存在顯著淹水風險，因此未來仍應持續強化排水設施管理及防洪規劃。

The Zuoying Second Naval Port expansion alters the Houjin River's downstream channel and estuary, potentially changing the basin's flood dynamics. This study uses the D-Flow Flexible Mesh (D-Flow FM) 1D-2D coupled model to assess the inundation potential before and after port construction. Validated with the 2024 Typhoon Gaemi, the model simulated various rainfall and return period scenarios. Results indicate that post-development drainage efficiency improves significantly due to the shortened river channel, offsetting tidal backwater effects. In most scenarios, the inundation area decreased, notably by 58% under a 6-hour 150mm rainfall event. Under extreme conditions (24-hour 650mm), the absolute inundated area was reduced by 353.06 hectares. Ultimately, the port expansion does not exacerbate overall flood risks but mitigates them by enhancing estuarine drainage. Nonetheless, extreme weather poses significant risks, necessitating ongoing flood management.

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