一維顯式有限解析法應用於石門水庫水力排砂之研究

Abstract

台灣的水庫淤積嚴重，故水庫於颱洪期間進行水力排砂以維持庫容乃當今水資源運用重要的課題。在各項水力排砂策略中，又以異重流排砂策略最適用於石門水庫。本論文延續前人研究，將已植入凝聚性沉滓傳輸機制的一維顯式有限解析法數值模式(許，2008)應用於石門水庫進行異重流排砂之研究，以符合石門水庫凝聚性沉滓的特性。根據前人研究，低高程排水口的洩水能力越大，則水庫進行異重流排砂的效率越好。模式中應用van Rijn (1984)所提之方法決定壩址處水深方向的泥砂濃度，配合水庫水位流量率定曲線求得不同設施放流量作積分，可算得其排砂量；將各設施之排砂量與上游入砂量相除可得各設施之排砂效率。 本研究模擬2008年辛樂克颱風與2009年莫拉克颱風，使用數值模式計算石門水庫異重流排砂策略的排砂效率，並與全洪程觀測資料作比較。模式並以2004年艾利颱風為案例，評估石門水庫既有設施防淤功能改善工程前後，不同的水庫低高程排水口洩水能力下，異重流排砂的效率。

The reservoirs in Taiwan have many problems related to sedimentation, so the sediment flushing during flood season to maintain the reservoir capacity is an important topic of water resources. Among the flushing strategies, venting density current is the most suitable one for Shihmen Reservoir. This study extends the previous research of Hsu (2008), which considered one-dimensional explicit finite analytic numerical model with cohesive sediment in reservoir, and applied the numerical model to the Shihmen Reservoir. According to previous studies, the larger capacity of the low-level outlet is, the better reservoir sediment flushing efficiency will be. The mass of flushing sediment of each outlet could be obtained by integrating the sediment concentration along water depth at the dam determined by the method of van Rijn (1984) and the outflow of each outlet determined by water stage-outflow rating curve. Therefore, the sediment flushing efficiency could be calculated by dividing the mass of flushing sediment to the mass of the upstream inflow sediment. By simulating the process of sediment flushing during Sinlaku typhoon in 2008 and Morakot typhoon in 2009, the flushing efficiencies of simulation results were compared by the observation data. And by simulating Aere typhoon in 2004, the flushing efficiencies of venting density current with different low-level outlet outflow capacities before and after the modification of the flushing facilities were also evaluated.