变动回水区河流交汇段水沙组合突变下河床冲淤规律研究

River confluence takes the main part of river system, and the operation of reservoirs impacts the motion characters of flow and sediment greatly and changes the pattern of erosion and deposition in the confluence zone. However, little study is about the effect of mutation of flow and sediment on the channel adjustment of river confluence in the fluctuating backwater region right now, which constrains the problem solving in the area of river regulation, fluvial environment, flood control, and inland navigation, etc. Field investigation, flume tests and numerical simulations will be adopted to investigate the flow and sediment characters of river confluence from the point of view of hydraulics and river dynamics. The study will focus on the flow structure, bed resistance and bed load transportation of river confluence under different backwater levels and flow rate ratios. The study will further figure out the channel adjustment mechanism during the upstream flood process and downstream backwater process. The results got by this study will provide the basis of flow and sediment characters of river confluence in the fluctuating backwater region, and improve the theory and protection manners of sediment disasters.

河流交汇区是水系发育的主要部分，水库的修建运行显著制约着交汇区水沙运动特性，从而调整局部区域的河床冲淤规律。而当前针对变动回水区的水沙组合突变诱发的水沙运动规律研究涉及较少，日益成为河流交汇区水沙运动规律、河流环境演变、防洪和通航保障条件等领域的瓶颈问题。本项目以变动回水区河流交汇段为研究对象，以水力学及河流动力学理论知识为基础，以野外调查、室内试验与数值模拟方法为手段，突出研究不同回水水位、不同水沙组合条件下交汇段水流结构、水流阻力、推移质输移规律，并进一步探明不同回水过程、干支流不同来水来沙过程组合条件下的河流交汇段河床演变规律。本研究成果，将为深入掌握变动回水区交汇河段水沙运动特性及河床演变规律提供支撑，并及时丰富和完善河流交汇区水沙运动灾害理论及其防治方法。

本项目以水库影响下的交汇河道河床演变为研究背景，以水力学及河流动力学理论知识为基础，以野外调查、室内试验与数值模拟方法为手段，突出研究了两方面内容：①下游水库不同蓄水水位影响下，处于水库变动回水区的交汇河道泥沙输移和河床冲淤规律。研究揭示了水位抬升或回落过程中干支流冲刷带和淤积带的迁移规律。开发了适用于水沙渐变过程模拟的平面二维水沙动力学模型（压力校正法求解，SIMPLER算法），并根据室内试验成果针对交汇段水沙的垂向非均匀特性对水沙数学模型进行了修正，提出了交汇河段输沙率和动床阻力修正计算方法；②干支流上游水库泄洪或自然洪水等非恒定水沙过程影响下交汇河道的水沙运动规律。开发了适用于水沙剧变过程模拟的平面二维水沙数学模型（Godunov格式），模型可应对激波捕捉、地形剧变和快速冲淤等问题，成功对交汇河道内强输沙影响下的洪水波演进过程进行了模拟。研究对丰富和完善河流交汇区水沙运动灾害理论及其防治方法，对交汇河道防洪和上下游水库调度亦有较强参考意义。