石門水庫垂直分層泥砂濃度監測技術研發及現場測試評估

Abstract

為評估水庫最佳防淤策略，水庫的來水來砂特性為重要關鍵，對於洪水監測，各水庫已施作多年，但泥砂監測資料目前僅石門、曾文與南化水庫有較多資料，其他水庫並不完整，且泥砂監測過程中問題頗多，故建立水庫泥砂資料是目前水庫整體防淤策略重要基本工作，依據「水庫泥砂監測技術暨防淤操作策略研究」計畫之水庫入庫泥砂監測技術初步規劃，各水庫泥砂濃度觀測儀器設置之步驟，主要先從入庫邊界渾水明渠流之緩流區及各排放口開始，原因在於水庫管理單位希望能掌握入庫含砂濃度進而得知入庫總砂量，以及得知各排放口或取水工附近高泥砂濃度變化情形，進而調整水庫放水與取水時間。石門水庫羅浮站在右岸斜坡建置分層抽水取樣設施及懸浮質濃度自動化觀測點，雖已提供較有根據的入庫泥砂估計，但受邊壁效應影響使其量測之河道泥砂濃度可能存在相當程度的變異性，如何獲得斷面代表性的含砂濃度，為河道輸砂觀測相當重要但較欠缺的一環。 因此本研究擬延續前期計畫成果，評估既有羅浮測站與新建主深槽觀測樁之差異性，精確量化入庫泥砂濃度歷線，建立全洪程水庫水砂運移規律，有效掌握水庫防淤操作時機及提升防淤效率同時進行探討集水區崩坍面積與入庫流木量及泥砂量之關係，跨域協調林業主管機關與水土保持主管機關聯合預防土砂災害，彙整土砂來源與林木資源化之參考。最後入庫邊界掌控集水區水砂資源控制站，提升水庫穩定供水與防淤功能，整合集水區相關治理單位，確實掌握土砂主要源頭，達到土砂管理與林木資源之分工合作。

To assess the best reservoir siltation prevention strategy, reservoir runoff sediment characteristic is the key to flood monitoring. This feature was monitored in various reservoirs but only Shihmen, Zhengwen and Nanhua reservoirs retained much more and complete monitoring information. Incomplete data and monitoring issues existed in other reservoirs, thus constructing a complete reservoir sediment database is the fundamental work in reservoir siltation prevention strategy. According to the preliminary planning in “Reservoir suspended sediment concentration monitoring technique and desiltation operation strategy research project”, suspended sediment monitoring equipment setup mainly begins from establishing monitoring stations at the flow buffer area of turbid water open channel flow and each outlet. This is mainly due to the reservoir management unit would wish to understand the inflow suspended sediment concentration to master the total sand inflow amount, and by knowing suspended sediment concentration variation of each discharge outlets or water, reservoir operation of water discharge or intake could be adjusted accordingly. Luofu monitoring station in Shihmen reservoir upstream had vertical layered water sampling equipment and automated suspended sediment concentration installed at the slope of the right embankment. Although there was relatively evidence-based sediment inflow estimation available currently, side boundary effect may induce substantial variation in river suspended sediment concentration measurement. Methods to gather representative sediment concentration at specific cross-sections are very important but yet lacking for river sediment transportation monitoring. This study is hence a successor of previous research outcome, to evaluate the differences between current Luofu river bank monitoring station and newly established observation pole in main channel, to accurately acquire inflow sediment concentration historical data, to establish reservoir sediment migration pattern during flood events, to effectively master optimal timing of reservoir desiltation operation and enhance desiltation efficiency. While at the same time, this study investigates relationship between landslide area within catchment region and amount of inflow driftwood and sediment, which would assist in cross-border coordination between forestry authorities and soil-water conservation authorities to jointly prevent debris flow disaster, and to compile all sources of earth and soil and forest resources management as reference. Control station monitoring the end inflow boundary could master catchment area water and soil resources, which could enhance reservoir water supply stability and siltation prevention, integrating catchment area management related authorities, in turn to master main sand source and achieve collaboration between soil management and forestry resources fields.