Numerical modeling of flood routing for the middle-lower Yangtze River system

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.