利用防淤隧道及沖淤池提升土砂去化量-以石門水庫為例

石門水庫為多目標水庫兼具供水、發電、防洪、灌溉與觀光，近年來受到極端氣候的影響使石門水庫發生複合型災害次數更加頻繁，其中，水庫淤積更是石門水庫急需解決的問題。目前石門水庫因土砂淤積造成庫容損失約三分之一，導致每年約需要操作4次以上庫容，才能滿足供水需求，面對土砂淤積問題經濟部水利署以多元清淤方式延緩水庫淤積，以水力排砂為主，機械清淤為輔，並預計於中程計畫(2021年)完成阿姆坪防淤隧道，除了提升防洪能力之外，預計每年可為石門水庫提升64萬立方公尺的排砂量，以舒緩庫區中游淤積問題。石門水庫淤積問題主要可區分為上游集水區攔砂壩、庫區中上游、壩前與下游沉澱池淤積，由「阿姆坪上游河道淤積物調查」鑽探結果顯示河道上游至下游沉積物粒徑由大逐漸變小，且根據阿姆坪防淤隧道設計單位以粒徑0.1mm作為區分可沖淤土砂(無價料土砂)與不可沖淤土砂(有價料土砂)之界定，有價料比例也由河道上游至下游逐漸減少。因此，本研究以阿姆坪防淤隧道工程為主軸，並將淤積問題區分為「上游集水區攔砂壩、庫區中上游粗顆粒土砂運輸不易」，與「壩前、下游沉澱池細顆粒土砂去化不易」兩大部分，將分別分析、提出建議。阿姆坪防淤隧道完工後預計於阿姆坪水域設置2艘水力抽泥船抽泥，土砂經由淤泥貯留設施篩分為有價料與無價料土砂，其中，本研究考慮影響浚渫作業物理因素、水利署販售土砂辦法及蒐集抽泥營運成本，在年清淤量達標下(64萬立方公尺)限制條件下，敏感度分析結果為：有價料數量、粒徑組成，對於販售價格以及營運益本比的影響最大，浚渫河道斷面29與31可達營運最大益本比4.5。無價土砂經篩分後，堆置於下游沖淤池，待颱洪事件來臨時沖入大漢溪。本研究以SRH-2D數值模式模擬沖淤池沖淤情形，其中，輸砂參數以水工模型試驗結果配合敏感度分析推估，並由不同定流量與配合包爾斯水庫演算法，計算颱風事件入流量作為邊界條件，模擬淤泥於堆置7日、16日與37日下之沖淤情形。本研究完成颱風事件包括蘇迪勒、麥德姆、蘇力與蘇拉颱風，在不同淤泥堆置日數下排砂比皆可達0.8以上。由本研究分析結果建議營運初期之土砂收入可用來投資上游集水區攔砂壩清淤，沖淤池則以沉澱池淤泥首先沖淤為主，使機械清淤能在非汛期持續清淤，由阿姆坪防淤隧道工程做為庫區中游清淤樞紐站，同時藉此提升石門水庫的土砂去化量以提高該工程之使用率。

關鍵字

阿姆坪防淤隧道； SRH-2D ；沖淤參數；去化量；不可沖淤土石

並列摘要

Shihmen reservoir is a multi-objective reservoir with water supply、power generation、flood protection、irrigation and tourism. Due to extreme climate, the frequency of compound disasters in Shihmen Reservoir has increase in recent years. Among them, losing one-third storage capacity caused by reservoir sedimentation is more serious than others. As a result, the Shihmen Reservoir need to be operated to provide more than four times the current storage capacity per year to meet the water supply demand. The Northern Bureau of Water Resources Agency (Ministry of Economic Affairs) using diverse policy with hydraulic flushing and supplemented by mechanical dredging to extend life of reservoir, and the " Amuping sediment bypass Tunnel " will be completed in 2021, not only can improve flood control capacity, bit also can discharge 640000 sediment cubic meter per year to alleviate the siltation problem. Shihmen reservoir sedimentation problem can be divided into the check dam of the upstream catchment area, the middle and upper reaches of the reservoir area, and the siltation of the dam front and downstream sedimentation tanks, and the report of "Amuping upstream channel silt investigation" show that the sediments diameter is gradually being small from upstream to downstream, and according to the design unit of the Amping anti-sludge tunnel, the particle size is 0.1mm as the distinction between the valuable sediment and the priceless sediment, and the percent of valuable sediment also gradually being small from the upstream to the downstream of the river. Therefore, in this study takes the Amuping sediment bypass Tunnel project as the main axis, and divides the sedimentation problem into the upstream sediment transport problem ,and downstream elimination sludge problem to analyze and suggest. Two hydraulic dredgers will be set up after the Amuping sediment bypass Tunnel project completed, and drawout sediment will be sizing into valuable sand and priceless sand through facilities, in this study considers the physical factors affecting the operation of the concrete and operation costs, and in the rivers sections 29 and 31 can reach the maximum operating ratio of 4.5, furthermore the sensitivity analysis results have the greatest impact on the operating benefit ratio with the valuable sand price; the priceless sand is sieved and placed in the flushing pool. This study uses the SRH-2D numerical model to Simulate the situation of sediment be flushing, among, the sand transport parameters are estimated by the hydraulic model test results and the sensitivity analysis, and the boundary conditions is calculated by reservoir algorithm to simulate flushing sludge situation which be placed 7、16 and 37 days , the typhoon events in this study included typhoon Soudelor, Medem, Su Li and Sura, and all of case flushing sediment ratio up to 0.8. From the analysis results of this study, it is suggested that more than the income in the initial stage of operation can be used to invest in the dredging of the upstream catchment dam, and the scouring and flushing pool is mainly based on the silt of the sedimentation tank, so that the mechanical dredging can continue to dredge during the non-flood period. The Amping anti-silting tunnel project is used as a dredging hub in the middle of the reservoir area, and at the same time, the amount of soil sand removal in the Shimen Reservoir is increased to increase the utilization rate of the project.