黄河下游游荡型河段洪水演进与河床变形过程的数值模拟

黄河下游游荡型河段的河床变形过程相当复杂，横向变形尤为突出，现有水沙数学模型一般仅能模拟河床纵向冲淤，不能模拟滩岸横向冲刷与崩塌，本文将平面二维水沙数学模型与粘性河岸冲刷的力学模型相结合，建立河床变形的平面二维混合模型。然后以黄河下游花园口至夹河滩的游荡型河段为例，采用该混合模型，首次较为全面地模拟了1982年汛期的洪水演进与河床变形过程。沿程最高水位、出口断面流量过程等计算值与实测值符合较好。计算结果还表现为大水时主槽冲刷，滩地淤积；小水时主槽淤积，滩地崩塌。该计算结果与游荡型河段的年内冲淤变化规律一致。

Numerical simulation of the flood routing and bed deformation processes in the wandering reach of the Lower Yellow River

The fluvial process is considerably complicated in the wandering reach of the Lower Yellow River, and the lateral or transverse bed deformation process is pronounced especially. This paper analyzes the state of the art of simulation techniques for the bed deformation in the Lower Yellow River, and such a conclusion is drawn that existing sediment mathematical models can only simulate the longitudinal bed deformation, cannot simulate the lateral deformation such as bank erosion and failure. Then a new 2D composite model consisting of a 2D flow sediment mathematical sub model and a riverbank erosion sub model is established in this paper for the first time, through using all kinds of enhanced measures. The new model not only can simulate the longitudinal and lateral deformation of riverbed, but also can be used to simulate the fluvial processes of natural rivers, especially the Lower Yellow River. Through using the proposed composite model, the flood routing and bed deformation processes during the August 1982 flood are simulated comprehensively. The maximum stage along the reach and the discharge hydrograph at the outlet so obtained are in good agreement with the observed data. Simulated results of the bed deformation processes show that during the flood season, the main channel scours and the flood plain deposits; during the dry season, the main channel deposits and banks of the floodplain retreat due to lateral erosion by flow and failure under gravity. The results accord with the annual law of scouring and deposition variation in the wandering reach.