不同量级洪水对黄河下游游荡段冲淤变化的影响

小浪底水库运用后，改变了进入黄河下游的水沙条件，引起了下游河道的再造床过程。以小浪底水库调控后的不同水沙过程为基础，研究这些不同水沙组合洪水在下游河道的演进过程及其对冲淤变化的影响，可为黄河下游“二级悬河”治理提供科学依据。文章首先介绍了模拟黄河下游游荡段实际断面形态下洪水演进的一维水沙耦合模型，并利用黄河下游1982年5—10月实测洪水资料对该模型进行了验证，计算所得流量过程、含沙量过程及沿程最高水位等均与实测值较为吻合；最后采用该模型计算了水沙总量相同条件下，不同量级洪水过程在下游游荡段的演进过程，分析了不同量级洪水对河床冲淤变化的影响。结果表明：不同水沙过程对下游游荡段冲淤变化有明显影响，洪峰流量为10000 m3/s及相应含沙量为60 kg/m3的水沙过程在下游游荡段淤积量最大，洪峰流量为4000 m3/s及相应含沙量为30 kg/m3的水沙过程在下游游荡段淤积量最小。从淤滩刷槽的综合效果看，洪峰流量为6000 m3/s及相应含沙量为40 kg/m3的洪水过程对于下游游荡段河床调整较为有利。

Influence of different flood hydrographs on riverbed erosion and deposition in braided reach of lower Yellow River

Since the operation of the Xiaolangdi Reservoir, flow and sediment entering the lower Yellow River (LYR) has been altered significantly and this leads to a process of channel re-forming in this reach. This study examines flood evolution under different combinations of flow and sediment and its effect on erosion and deposition based on the water and sediment regimes regulated by the reservoir. A one-dimensional flow-sediment coupled model is developed to simulate flood routing along the braided reach of LYR, and it is verified using the measurements of a flood event occurring in this reach from May to October 1982. Calculations agree well with the measurements, including the calculated flow, sediment concentration and variation in flood peak level along the channel. Then, we regulate this 1982-flood into different flow and sediment processes by fixing the total volumes of flow and sediment but adopting different peak discharge Qmax and peak sediment concentration Smax in different processes. Using these regulated flood processes and our coupling model, we calculate flood routing and channel deformation, and analyze the influence of different flow-sediment processes on riverbed deformation in the braided reach. The results show that different flow-sediment processes produce significantly different channel deformation. In term of channel deposition volume, the combination of Qmax = 10000 m3/s and Smax = 60 kg/m3 would create the largest while Qmax = 4000 m3/s and Smax = 30 kg/m3 the smallest. According to the comprehensive effect of floodplain deposition and main-channel scour, the combination of Qmax = 6000 m3/s and Smax = 40 kg/m3 would be most advantageous to riverbed evolution in the LYR braided reach. Keywords: one-dimensional morphodynamic model; overbank flood; erosion and deposition; braided