豪雨期間懸浮質泥砂濃度變化之探討分析

臺灣平均降水充沛，但在世界各國中仍屬缺水國家，主要歸因於河川坡陡流急造成地表水儲水不易，因此水庫蓄水為不可或缺的水利建設。然臺灣各集水區土壤沖蝕崩塌常伴隨著颱風豪雨侵襲而大量產出泥砂，致使水庫產生異重流而有泥砂淤積問題。為有效減緩石門水庫淤積並延長其壽命，經濟部水利署於近年著手推動水庫排洪防淤工程，利用颱洪期間將大量上游來砂排放至水庫下游，將泥砂回歸下游河道，期能有效維持庫容以永續利用水資源，但對下游河道之泥砂懸浮質濃度必然產生影響。本研究利用現地懸浮質泥砂濃度採樣數據，並採用擬似二維輸砂數值模式進行水理輸砂模擬，探討在颱風期間，石門水庫曾進行排砂操作時，下游河道之逐時濃度變化。現地懸浮質泥砂濃度採樣位置共包含大漢溪本流之後池堰、鳶山堰、城林橋；淡水河本流之中興橋、關渡橋；新店溪直潭壩及基隆河百齡橋之採樣資料。數值模式則利用上述資料進行水理輸砂模擬演算。研究結果顯示，水庫排砂操作造成局部河道濃度短時間內上升，但其濃度隨著水流運移至下游鳶山堰時已有遞減現象，對鳶山堰取水會造成影響，但其影響取水時間少於8 小時；若搭配現地採樣數據，從鳶山堰運移至河口之泥砂濃度則遞減更多，約在排砂結束兩天內降至1000 ppm 以下。未來若能掌握河道上游來砂懸浮質濃度監測資料，則可模擬分析下游河道沿程影響程度，可提供水庫排砂操作或淨水廠取水時機相關資訊，期能在對下游影響程度最小之情境下，有效維持水庫現有庫容。

關鍵字

泥砂淤積；懸浮質採樣；數值模式；水庫排砂

並列摘要

Taiwan is suffering a desperate shortage of water even the annual average rainfall is abundant. The steep river bed cause surface water hardly to storage. Hence, the Reservoir is very important construction in Taiwan. However, reservoirs in Taiwan encounter deposition problem due to sediment yield during typhoon flood event. The density current flow to dam front, and deposit in reservoir bed. Therefore, Water Resources Agency conduct a series of Integrated Desiltation Strategies, to mitigate the sedimentation and extend the life of Shihmen reservoir. However, revervoir sedimentation return to downstream should be affect the suspended solid concentration (SSC) of river. In this study, field survey data and numerical model used to investigate the variation of downstream SSC. The field survey data location include Hochi Weir, Yushan Weir, Chenglin Bridge, Zhongxing Bridge Guandu Bridge in Dahan River; Zhitan Dam in Xindian River; and Bailing Bridge in Keelung River. It also could be adopted to boundary condition in numerical model, and exploited to be calibration and verification. The results show, although reservoir sediment relsasing increases the SSC rapidly of downstream local river, it decreases along the river. It affects Yushan Weir water intake less than 8 hours. SSC decreases significantly from Yushan Weir to river mouth, it declines less than 1000 ppm in two days. In conclusion, in the future, we can use numerical model to analysis the affect of downstrean river, and exploit the field survey data to montior control points. These Not only maintain the storage of reservoir, but minimize the downstream impact of SSC.

並列關鍵字

Sediment deposition ； Sediment releasing ； Field survey data ； Numerical model

國際替代計量

豪雨期間懸浮質泥砂濃度變化之探討分析

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