臺灣受地形陡峻、河川短促及降雨時空分布不均影響，水資源調配長期面臨豐枯差異大與供水穩定性不足等問題；同時，既有水庫淤積與新建大型水庫受限，使沿海地區如何利用原本入海之河川淡水成為值得評估的替代水源方向。本研究以屏東東港溪與大鵬灣為案例，建立整合側堰引水、懸浮泥砂輸入、有效庫容衰減與水庫供需操作之分析架構，探討取水工設計與庫容條件對海岸水庫長期供水表現之影響，並以 NSGA-II 多目標最佳化方法分析工程成本與供水可靠度之折衷關係。
本研究以堰高、堰寬及水庫蓄水深度為主要設計變數，採用 De Marchi 側堰理論估算物理可引水量，並以 Rouse 濃度剖面估算不同取水層位之懸浮泥砂輸入，再將泥砂淤積轉換為有效庫容衰減。河川取水保留流量採 12.19 m³/s 作為操作基準，實際入庫量同時受到河川可用流量、引水道通水能力與水庫剩餘容量限制。供水績效分別採時間可靠度與體積可靠度評估，並以 1000～8000 萬 m³/月之不同供水責任情境檢視系統表現。最佳化分別建立「成本－時間可靠度」與「成本－體積可靠度」兩組二目標問題，泥砂量與期末有效庫容則作為非支配解之衍生評估指標。
結果顯示，堰高與堰寬對系統具有相互制衡作用：較高堰高可降低入庫泥砂量，但當堰高接近可越流水深上限時，會因引水不足使可靠度快速下降；堰寬增加可提升引水能力，但在河川可用水量與剩餘庫容限制下會逐漸出現邊際效益而遞減。庫容水深則提供調蓄與抗淤積緩衝能力，其效益在中高需水量情境下較為明顯。代表性最佳化結果顯示，3000 萬 m³/月情境可於較小庫容與取水設施下達到時間與體積可靠度皆為 1；6000 萬 m³/月情境可取得時間可靠度 0.996、體積可靠度 0.999 之方案；8000 萬 m³/月情境之最高時間可靠度約為 0.917，顯示系統在高供水責任下已接近其供水能力上限。
最佳化結果顯示，成本與可靠度之間不存在單一絕對最佳設計，而是形成一組非支配解集合。體積可靠度導向下，成本－可靠度前緣較為連續，可反映成本增加所換取之總缺水量改善；時間可靠度導向下，因月份供水達標採二元判定，前緣較容易出現分段與門檻特徵。整體而言，海岸水庫設計需同時檢視取水能力、庫容規模、需求水準、泥砂輸入與工程成本，並由非支配解中依供水目標與風險容忍度選擇合適方案。

Coastal reservoirs provide a potential alternative for storing river water that would otherwise discharge directly to the sea, but their long-term performance depends on the interaction among diversion capacity, sediment inflow, storage loss, and water demand. This study uses the Donggang River and Dapeng Bay in Pingtung County, Taiwan, to develop an integrated assessment framework for a second-generation off-channel coastal reservoir. Weir height, weir width, and reservoir storage depth are treated as design variables. De Marchi side-weir theory is used to estimate hydraulic diversion capacity, the Rouse concentration profile is applied to represent vertical suspended-sediment distribution, and sediment deposition is converted into effective-storage depletion. Reservoir operation is evaluated using time reliability and volumetric reliability under monthly demand scenarios of 10–80 million m³. Two separate NSGA-II bi-objective optimizations are conducted for cost versus time reliability and cost versus volumetric reliability. Results show that increasing weir height can reduce sediment inflow but eventually causes diversion insufficiency, whereas increasing weir width improves diversion capacity with diminishing benefits. Greater storage depth enhances regulation and sedimentation buffering. At 30 million m³/month, both reliability measures can reach 1.0 with relatively small storage and intake dimensions. Under a 60 million m³/month demand, a representative design reaches time and volumetric reliabilities of 0.996 and 0.999, respectively; under 80 million m³/month, the maximum time reliability is about 0.917. The results demonstrate that coastal-reservoir design should be selected from non-dominated trade-off solutions rather than from a single extreme objective.

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