黄河下游不同流量级洪水冲淤特性的计算与分析

Numerical simulation and analysis of scouring and silting effects of different discharges on Lower Yellow River

运用黄河下游水文学冲淤计算模型,对2002年和2009年小浪底水库调水调沙试验方案进行了计算,计算结果与实测值吻合较好。以2002年调水调沙总水量为控制指标,选取2002年地形(长期淤积)和2009年地形(长期冲刷)为边界条件,以清水下泄和来沙系数为0.01 kg.s/m6两类洪水,按照不漫滩、平滩和小漫滩三种方案,计算了黄河下游河道在不同边界条件下的滩槽冲淤量,以及各河段平滩流量的变化特征,对比分析了两类洪水在不同方案下的滩槽冲淤效果。对于清水冲刷,当以下游河道的最大平滩流量控制小浪底水库下泄流量时,全下游的冲刷效益最大。对于来沙系数为0.01kg.s/m6的高含沙水流,流量级越大,全下游的主槽冲刷量和平滩流量增幅越大,但淹没损失也较大。需要通过进一步研究,得到使全下游冲刷效益和淹没损失达到最优化的流量,作为小浪底水库的调控下泄流量。

In this study,the water-sediment regulation tests conducted for the Xiaolangdi Reservoir in the years of 2002 and 2009 are simulated numerically to examine the scouring and silting effects of different discharges on the Lower Yellow River.It is found that the simulated results are in a fairly good agreement with the measured data.In the numerical simulations,the water amount used for the 2002 water-sediment regulation test is selected as the target control quantity;the shape of 2002 river terrain（due to long-term river siltation） and the shape of 2009 river terrain（due to long-term river erosion） are set as the boundary conditions;two water discharges scenarios are simulated including a clear-water discharge and a water discharge with a sediment-content coefficient of 0.01;three downstream overflow situations are considered in accordance with no overflow,bankfull and a little overflow of floodplain in the Lower Yellow River.For the clear-water discharge scenario,the scouring and silting effects on the entire Lower Yellow River reach its maximum level,when the flow discharged from the Xiaolangdi Reservoir is regulated equally to the bankfull discharge.For the 0.01-sediment-content discharge scenario,the scouring and silting effects on the main channel increase with increase of the flow discharged from the Reservoir;the growing rate of the bankfull discharge in the Lower Yellow River increases with this flow discharge as well.This could lead to significant inundation losses in the Lower Yellow River.It is suggested that more studies be conducted to determine the optimal flow discharge from the Xiaolangdi Reservoir for reaching an optimized scouring and silting effects and less inundation losses.