水庫操作對於短期洪災與長期缺水風險分析之研究

Abstract

本研究之目的在於提出一方法及研究分析步驟，以供評估水庫防洪操作在不同之起始水位下，對長期枯水期間缺水及短期颱風期間下游控制點溢流之風險。本研究蒐集歷史颱風期間之水庫洪水入流歷線，藉由蒙地卡羅模擬法合成大量之水庫入流量歷線，放入防洪操作模式模擬得到防洪操作結束之水庫水位，並以此為起始條件由水庫優化調配模式，計算枯水期間之供水情形；颱風期間模擬防洪操作時之水庫放水量，則由倒傳遞類神經模式計算河道下游之水位變化，進而求得間下游控制點颱風期間之最高水位。最後經由風險分析之方法以考量安全邊際之方式，計算得到不同水庫防洪起始下，枯水期間之缺水及颱風期間下游溢流風險。本研究以台灣大漢溪流域石門水庫作為研究區域，研究結果顯示不同之水庫防洪起始水位，對於需水點枯水期缺水風險之變化影響甚大，且缺水風險隨著水庫上限值之增加而明顯降低，但對於颱風期間下游控制點溢流風險之變化影響甚小，且溢流風險隨著水庫上限值之增加而些微升高。由上述分析結果，建立洪災與缺水風險關係圖，以此作為水庫操作者及決策者，制訂洪汛期間水庫最佳起始水位之參考。

This study proposes a methodology to assess the risk of the water shortage during a drought period and the risk of the downstream over-levee flows during a flood period based on the reservoir operation rules for flood control. These rules are defined by upper limits (or flood control storage zone). Through a Monte Carlo simulation, a series of hydrographs are generated to represent the reservoir inflow during a flood period based on historic typhoon events. This series of generated hydrographs are then applied to a reservoir flood operation simulation model. The simulation model calculates the water levels of reservoir at the end of a flood period and the reservoir release during the typhoon events. Reservoir release is used to calculate the water level at downstream control locations for evaluation of a short-term over-levee risk. The ending water level of the reservoir is used as the initial condition for a water distribution optimization model that evaluates drought conditions for long-term water supply. By applying risk analysis, an assessment is made on the risk of both the water shortage during a drought and over-levee flows during flooding seasons. Based on the results of the risk analysis, we evaluate the relationship among upper-limit sets, shortage risk, and over-levee risk and also provide reservoir operation suggestions based on the risk evaluation.