三峡库区淤沙性分汊河段演变关键机理研究及数值模拟

Abstract: The Three Gorges Reservoir is a typical mountain river reservoir. After its implementation, deposition of fine-grained sediments and evolution of bars in the backwater reach have directly influenced the stability of braided channel sections and the navigation conditions. The morphology of river channels is determined by the interaction of fluid flow, sediment transport and geomorphologic characteristics. Although various studies have provided a great deal of information on the response of channel-bed configurations in the form of sand bars and bedforms, none is universality. Few preliminary studies of the fine-grained sediment movement and the mechanics of sand bar formation are offered, to explain the new problem in the Three Gorges Reservoir. Based on the River dynamics, Soil mechanics, and Non-linear Dynamics, this project proposes to approach the process of sediment transport, erosion, and deposition in the TGP by field observations, physical experiments, theoretical analyses, and numerical simulations. The formulae of the settling velocity and incipient velocity will be established from the laboratory flume with the sediments from the field, by taking into consideration the complex properties of the sediment itself and the effects of water depth; a discriminant criterion will be developed to distinct deposition, erosion and transport zones in the combination with the experimental and field measurements. The lateral migration equation will be modified to better describe the evolution of sand bars with the typical river model. Based on the above systematic experimental research results, an improved 2-D depth-averaged coupled numerical model for hydrodynamic, sediment transport and river morphological adjustment will be established. The sediment transport submodel will take into account the formulae from the experimental study of the fine grained sediments; the river morphological adjustment submodel will include the lateral migration equation to simulate the mode of bar growth and migration, so that it will be capable to simulate the pattern process with the sand bars in the TPG. The extended 2D numerical model will be applied to investigate the main controls of sand bar evolution and aid in the quantitative prediction the development of the channel pattern in the Three Gorges Reservoir. Results of this study will further enrich the theory foundation of the mechanics of sediment transport in the mountain river reservoirs, and provide technological support to the management of the TGP operation and waterway construction within the Three Georges Reservoir area.

摘要：三峡水库是典型的山区河道型水库，工程蓄水以来，库区细沙淤积和洲滩演变直接影响分汊河段河势稳定与航运畅通；其水流运动、泥沙冲淤、洲滩形态三者具有复杂的内在响应机制，理论分析难度较大。在以往的研究中，对山区河道型水库中细沙输移特性及淤沙浅滩的演变机理尚缺乏系统的分析。本项目拟采用多种研究手段，基于河流动力学、土力学及非线性动力学等理论，从内在动力机制出发建立库区分汊河段细沙沉降、起动及冲淤判别的数学模式与淤沙浅滩消长的动力学模式；以此为基础改进现有河流模拟数值模型的悬沙输移模块与滩岸淤长模拟技术，构建能够准确揭示三峡库区淤沙性分汊河段演变关键机理的平面二维水沙动力学耦合模型。利用改进的数值模型，系统分析水沙等多方面控制因素与库区淤沙性分汊河段演变的响应机制，进一步量化预测其河势演变趋势。研究成果将丰富山区河道型水库泥沙运动力学理论基础，为三峡水库的运行及库区航道发展规划提供科学依据。

三峡水库作为典型的山区河道型水库，库区分汊河段细颗粒泥沙输移特性与其淤沙浅滩演变(如淤泥、浮泥状淤积物的运动)的响应机制不仅满足水流泥沙动力学规律，同时也受到河道地貌水沙特性影响，具有一般水库的共性与自身的特性。针对细沙淤积引起的河势演变所导致的通航问题，有必要通过对水沙响应机制的系统研究，得到三峡库区淤沙性分汊河段演变的关键机理，从而为库区的航道的整治提供重要的理论与数据支撑。 本项目通过多种科学研究手段，从内在动力机制出发，对库区典型分汊河段细沙运动规律与淤沙浅滩演变机理进行了系统研究，建立了能准确揭示细沙输移特性及淤沙浅滩消长的动力学模式，构建了具备模拟三峡库区淤沙性分汊河段演变过程能力的平面二维水沙动力学耦合模型，定量地分析了不同水沙条件下三峡库区淤沙性分汊河段演变关键因素响应机理及其冲淤变化趋势。项目所取得的研究成果进一步丰富了山区河道型水库泥沙运动力学理论基础，亦为三峡水库的运行及库区航道发展规划提供了一定的数据支撑，具有重要的科学意义与工程指导价值。