台灣地區之大型水庫均為年用型水庫，每當豐水季之降雨量不豐以致水庫蓄水不足時，往往會在隔年的枯水期發生缺水現象。若水庫之蓄水量經評估可能不敷未來枯水季月份之計畫供水所需，則宜事先規劃枯水期限水標準，以適切調配各標的用水之供水量，使整個枯水期得以共同承擔乾旱的衝擊，避免嚴重缺水集中發生在枯水期末，減少因缺水而導致之經濟發展受損、民生不便等負面影響。
  本研究考慮水庫蓄水可能不足計畫供水所需之情形時，在枯水期水源的序率過程下，估算水庫供水之缺水風險及期望缺水量，以利評估未來數個月的枯水期水庫限水操作策略。
  研究中以翡翠水庫為實例，操作上以月為時間單位，依據多變量ARMA模式繁衍南、北勢溪同一時刻具相關性之94,000年合成流量序列，建立南、北勢溪之一階二變量聯合移轉機率矩陣。因係用水調度，期間不採用規線之限水策略，穩定供水目標直接設定為計畫用水量之100%、90%、80%及70%等不同標準，演算各離散等級蓄水之蓄水機率，進而估算缺水風險及期望缺水量，據以評比未來數個月不同水庫蓄水操作策略。

Reservoir operations are mostly based on annual cycle in Taiwan. It is very likely to suffer water shortage in the ensuing dry season if the rainfall is less than usual in the wet season. When the storage of a reservoir is assessed not capable to meet the water demand of future months in the dry season, the authorities should plan the water supply reduction policies in advance to alleviate the impact of probable water shortage on the civil life and economic development.
This thesis adopted simulation method to compute the probable deficit of water supply and its risk under the conditions of different predetermined demands in the near future. The occurred probabilities of discretized reservoir storages of each month in dry season were simulated with stremflows of the last month, the storage of current month and streamflow transitional probabilities. The probable water shortages and their occurrence probabilities provided useful information in the decision-making of discounted water supply policies.
The Feitsui Reservoir was taken as a case study. A multivariate auto-regressive-moving average (ARMA) model was established for historical monthly streamflows of Peishih Creek and Nanshih Creek by accounting the cross correlation between the two creeks. This ARMA model generated 2,000 sets of 47-year synthetic streamflow series. Twelve transitional probability matrices with 125x125 elements were built for every month with the above synthetic streamflows. Twenty scenarios of four reduction rates and five initial storages were simulated for expected water shortages and their probabilities during drought season. The discounts of water supply were set as 0%, 10%, 20% and 30% of water demand. The averaged daily water supply was estimated for every reduction rate and initial storages.

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