Numerical modeling of flood routing for the middle-lower Yangtze River system
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摘要: 以长江中下游(宜昌-大通)防洪系统为对象,在水文、河道及湖盆地形现状条件下,建立了一个能适应各种复杂条件的一二维非恒定流模型,来进行长江干流、河网、湖泊、分蓄洪区垸及水库的洪水演进和调度仿真.所建模型的洞庭湖部分采用无结构网格二维非恒定有限体积格式,以适应湖区复杂的边界形状和保持水量平衡.河网区部分采用一维非恒定流显隐结合的分块三级算法,以准确实现河网汊点流量的自动分配和往复流动.为了提高模拟精度和扩展模拟功能,在水流数值模拟的范围内侧重讨论了内外动边界处理、分蓄洪运用及阻力项计算等环节,提出了合理可行的数值处理方法.采用20世纪80年代至90年代共6年汛期洪水资料对所建模型进行了严格的率定和检验,高精度的模拟结果证实了模型的合理性和有效性.Abstract: In order to study flood management problems of the middle-lower Yangtze River system,a 1D-2D combined unsteady flow model is developed for simulating complex flood routing behaviors in the river-lake coupled system.A finite-volume method for computing 2D unsteady flows on an unstructured mesh is used to fit the complex configuration of the Dongting lake and to preserve mass balance; a 1D explicit-implicit-three-level difference scheme is applied to simulate branched and looped river network flows for accurately realizing automatic allocation of discharges at channel junctions and reversing flows.To increase modeling accuracy and extend modeling capacity,some essential problems arisen in the process of model building,including treatments of interior and exterior boundary conditions,flooding storage-discharge effects,and calculations of variable resistance terms,are discussed.Finally,the model is calibrated and verified against five flood events observed during 1954 - 1991 for illustrating excellent performances of this model.
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