台灣普遍利用美國陸軍工兵團研發之缺水指標評估供水系統之特性，然而該指標無法明確描述系統於模擬時期的缺水特性，例如：發生缺水之機率、缺水強度或缺水延時等。因此本研究利用可靠度（Reliability）、恢復度（Resiliency）、脆弱度（Vulnerability）等三項風險指標的概念定義永續性指標（Sustainability Index），藉以表示系統出錯機率、由錯誤回復正常運作的機率、受損程度之嚴重性，評估供水系統之乾旱風險。 本研究選定桃園地區的石門供水系統作為研究區域，以1964~2004年歷史日流量做為入流量資料，利用下游日需水量增加以及系統有效庫容折減等情境進行模擬，探討規線運作與否對於缺水指標和各項風險指標的差異。 研究結果顯示，採取規線操作的供水策略，由於系統先行採取限水措施，致使缺水天數和單次連續缺水量增加，其可靠度值與脆弱度值皆會小於無規線操作的供水策略。當模擬庫容量為80%現行庫容量以上時，規線操作的放水策略能有效提升恢復度，且一旦發生缺水情況，規線操作的系統其恢復度隨著日需水量上升呈現緩慢下滑的趨勢，代表此時運用規線之供水系統出錯時較容易回復正常供水，系統永續性較高。當模擬庫容量低於80%現行庫容量，此時缺水情況加劇，規線運用與否對於系統回復供水之能力沒有太大影響。 永續性指標是以各項風險指標的連乘積表示，藉此評估各項風險指標間不同的狀況。模擬結果發現永續性指標多被恢復度和脆弱度影響，受可靠度影響極小。當系統庫容量設為80%現行庫容量以上時，規線操作能有效提升永續性指標（Sustainability Index），系統維持穩定供水的能力較佳。In Taiwan, Shortage Index (SI) developed by Hydraulic Engineering Center of U.S. Army Corps of Engineers is traditionally applied to evaluate water supply system. However, Shortage Index is limited because it does not describe the characteristic about the water shortage events. This study uses factors such as reliability, resiliency and vulnerability as indicators. These indicators are meant to represent the possibility of deficit event happened, the possibility of the system recovered after the occurrence of a failure, and the severity of its damage, respectively. Sustainability Index, combining reliability, resiliency and vulnerability, is defined in this study to estimate drought risk of the system.The Taoyuan water supply system was chosen as a case study. To take into account cases where water demand increased or storage capacity decreased, this study utilized inflow data from 1964 to 2004 to simulate the difference between the application of the hedging and unrestricted operation.According to the result, the system adopting the hedging would extend the duration of the failure event. Although it reduces the value of reliability and vulnerability, the value of resiliency would be promoted especially in those cases where the capacity are set to be more than 80% of the current capacity. In terms of Sustainability Index, the operation of the hedging is better than the unrestricted operation. It is particularly significant in those cases where the capacity are set to be more than 80% of the current capacity.
