大壩建設造成河川大量流量被阻截，改變生態系統中大範圍的非生物和生物棲息條件，被認為是全球河流最嚴重的人為影響之一。本研究的目的是結合乾旱指標應用於環境流量管理策略中，期望能同時滿足人類和環境用水需求。在乾旱指標中，選用計算簡單，且能根據需求選擇時間尺度的標準化降水指數(SPI)來進行計算，在根據標準化降水指數對應的放水條件下，開發了五種環境用水的釋放情境：（一）沒有環境用水釋放，（二）Q_95加上不同比例的旬平均流量，(三)前人研究之推薦流量（四）Tennant方法建議的環境流量，以及（五）改變農業灌溉的基準供水量。在所有情境下計算並比較缺水指數和水文改變指標。本研究使用了易取得的雨量資料，同時考量水庫現有蓄水量的環境用水計算方法，提供台灣水庫管理者在環境流量管理和規劃，有用且嶄新的參考策略。
本研究以曾文、烏山頭聯合操作水庫系統作為研究區域，整理歷史雨量與水庫操作資料，開發一套水庫操作模擬程式，在原有的操作規則上，另外提出東口堰引流公式、和曾文水庫防洪溢流公式，以及環境用水的打折比例，使每年的模擬過程能更有一致性。最後使用修正缺水指數比較各情境的缺水情況，結果指出：(1)五個情境大致分成三種等級，情境四缺水指數最高，因為此情境釋放的環境用水最高，進而影響水庫蓄水量和供水打折比例。(2)情境二、情境三缺水指數差異不多，皆略低於情境四，根據初始蓄水量設定，有時情境二較高，有時情境三較高。(3)情境一和情境五為供應最多人為用水的方案，因為情境一未額外提供環境用水，情境五供應較少的農業供水，故此兩情境缺水指數最低。
此外，藉由水文改變指標分析，探討哪一種釋放環境用水的情境對回復河川到自然流態的幫助最大，結果指出：於三種不同初始蓄水量設定時，皆有類似的趨勢，以平均初始蓄水量設定為例，在20個年中選定的9個IHA指標中，情境五在共180個IHA中，以31.0%高於其他情境，接著是情境二(26.2%)、情境一(18.3%)、情境三(13.1%)，最後則是情境四(11.4%)。最後，根據水庫模擬結果、修正缺水指數與水文改變指標分析後，建議以情境二作為曾文水庫釋放環境用水之參考方案。

Construction of dams at the upstream of rivers, to store water resource, might modify the abiotic and biotic elements in the ecosystem, and it is considered one of the most significant human impacts on rivers worldwide. In this study, the selected drought indicator was the Standardized Precipitation Index (SPI). And it was applied to release environmental water to balance human needs and environmental requirements. Five scenarios were developed based on the baseline of water supply and environmental water release. The scenarios were: (1) no release of water for environmental flow, (2) Q_95 plus ten days of average flow in different proportions, (3) flow rate recommended from previous studies, (4) environmental flows recommended by Tennant method, and (5) changes under the baseline allocation of water for agricultural irrigation. The study was divided into two parts. The first part used the Modified Shortage Index (MSI) to compare the water shortage in each scenario. The results indicated that: (1) The five scenarios were roughly divided into three levels, and the MSI of scenario four was the highest, because the environment water released by this scenarios was the highest, which in turn affect the reservoir water storage capacity and water supply discount ratio. (2) There was not much difference between scenario 2 and scenario 3 water shortage index, which are slightly lower than scenarios 4. According to the initial water storage amount, sometimes scenarios 2 was higher, and sometimes scenario 3 was higher. (3) Scenario 1 and Scenario 5 were the schemes for correcting the lowest water deficit index. Because the scenarios did not provide additional environmental water, and scenario 5 supplied less water for agricultural, these two scenarios had the lowest water shortage index. The second part was to discuss the scenarios through hydrological alteration indicators. In the nine IHA indicators selected in the 20 years, the number of each scenario was the closest to the natural hydrological alteration indicator. The average of initial water storage was set as an example. In total of 180 IHAs, scenarios 5 was higher than other scenarios with 31.0%, followed by scenarios 2 (26.2%), scenarios 1 (18.3%), scenarios 3 (13.1%), and finally scenarios 4 (11.4%). Water deficient ratio and eco-hydrological indicator were calculated and compared in all cases. This study used an environmental flow calculation method, using readily available rainfall data. The actual water storage procedure of the reservoirs was considered at the same time. This study could provide sufficient information for reservoir managers in Taiwan to make more suitable and sufficient management in environmental flow and river planning.

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