Sediment deposition of Three Gorges Reservoir and its impact on the reservoir area in recent 20 years

Abstract

泥沙问题是三峡工程建设与运行中的关键技术问题之一,只有妥善处理好泥沙问题,才能保证三峡工程长期有效使用,维持水库功能的全面发挥。本文首先结合实测水文、河道地形观测资料,对三峡水库运行近20年来的泥沙淤积特性及水库排沙比进行了较为全面的分析研究,并与已有研究成果进行了对比;其次,围绕防洪、航运以及坝前段的泥沙淤积等方面,进一步分析了水库淤积产生的影响。结果表明:三峡水库蓄水以来,在不考虑区间来沙的情况下,三峡水库共淤积泥沙20.484亿t,近似年均淤积1.102亿t,水库排沙比为23.6%,水库年均淤积量为原论证预测值的33%。其中,库区干流段累计淤积泥沙17.835亿m³(变动回水区冲刷0.694亿m³;常年回水区淤积18.529亿m³),淤积在水库防洪库容内的泥沙为1.648亿m³(干、支流分别淤积1.517亿m³和0.131亿m³),占水库防洪库容的0.74%,“十一五”攻关阶段研究得出的多年平均淤积量及排沙比较实测值均偏大,变动回水区冲淤则出现反向的情况,主要原因是研究采用的入库沙量偏大以及近期河道采砂和水库优化调度等影响。水库淤积对防洪库容和地下电厂的影响尚小,对库区部分水道航道条件产生了一定的影响,应加以关注。;Sediment problem is one key technical issue in the construction and operation of the Three Gorges Project. Only by properly handling the sediment problem can we ensure the long-term effective use of the Three Gorges Project and maintain a full play of the reservoir function. In this paper, the characteristics of sediment deposition and the sediment discharge ratio of the Three Gorges Reservoir (TGR) in the past 20 years have been comprehensively analyzed and studied based on the observed hydrological and river topographic data, and compared with the existing research results; Secondly, the influence of reservoir sedimentation is further analyzed in terms of flood control, navigation and sediment deposition in front of the dam. The results show that since the TGR impoundment, the total sediment deposition of the TGR is 2.0484 billion tons, approximately 110.2 million tons per year, the sediment discharge ratio of the reservoir is 23.6%, and the average annual sediment deposition of the reservoir is 33% of the original demonstration prediction value without considering the sediment from the interval. Among them, the accumulated sediment deposition in the main stream section of the reservoir area is 1.7835 billion m³ (69.4 million m³ scoured by the fluctuating backwater area; 1.8529 billion m³ silted by the perennial backwater area), and the sediment deposition in the reservoir flood control storage capacity is 164.8 million m³ (151.7 million m³ silted by the main stream and 13.1 million m³ silted by the tributary respectively), accounting for 0.74% of the reservoir flood control storage capacity. The average annual sediment deposition and sediment discharge measured during the 11th Five Year Plan period are relatively large, the scouring and silting in the fluctuating backwater area are reversed, mainly due to the influence of the large amount of sediment entering the reservoir, the recent sand mining in the river channel and the optimal operation of the reservoir. The influence of reservoir siltation on flood control storage capacity and underground power plant is still small, and it has a certain impact on some waterway conditions in the reservoir area, which should be paid attention to.