黄河下游高含沙洪水演进及河床冲淤过程的数值模拟

Numerical simulation of the process of hyperconcentrated flood routing and channel deformation in the Lower Yellow River

高含沙洪水通过黄河下游河道时往往发生严重淤积,因此,数值模拟研究高含沙洪水的演进过程,对理论研究及实际工程需求均具有重要意义。以往的泥沙数学模型通常不考虑高含沙量对水流控制方程的影响,而这将会影响高含沙洪水演进过程的模拟。本文建立了黄河下游高含沙洪水演进过程的一维非恒定非均匀沙数学模型,该模型不仅在水流控制方程组中采用浑水的连续方程与动量方程,而且通过引入滩槽划分及"二级悬河"处理等技术考虑黄河下游复杂地形下的水沙演进。以1977年的典型高含沙洪水过程为例,分析高含沙量对洪水演进的影响,并率定出模型中的恢复饱和系数、不饱和系数等关键参数。将率定后的模型参数应用于1992年下游实测洪水的模拟,验证模型的适用性。计算结果表明:考虑高含沙的影响后,洪峰流量、水量、传播时间的模拟误差减小,说明在数值模拟高含沙洪水的演进中有必要采用浑水控制方程。

Hypereoncentrated floods usually cause serious deposition in the Lower Yellow River, which play very important roles in flood routing and channel adjustment. Therefore, numerical study on hyperconcentrated flows is helpful to sediment transport theory and practical engineering. Among previous models, the influence of sediment concentration on the process of flood routing was often ignored in the flow governing equations, which will influence the real flood routing. In this paper, a one-dimensional model for simulating hyperconcentrated floods is proposed, in which continuity and momentum equations for turbid flows are adopted. In addition, techniques such as sectiondivision and secondary-perehed river are introduced. Parameters in this model is calibrated by the hyperconcentrated flood occurred in 1977, such as saturation recovery coefficient and saturation coefficient. Then the flood occurred in 1998 is used to further verify the model. Simulated results showed that, the sediment concentration plays an important role in the process of flood routing, which influences the peak discharge, maximum sediment concentration, etc. After adopting the turbid flow governing equations, simulated results agree better with the measured data. So, it is necessary to adopt the turbid flow governing equations in one-dimensional simulation, and the model is suitable for the simulation of floods in the Lower Yellow River.