Using nested grids to simulate sediment transport in the Caspian Sea with account taken of global and local scales

Introduction. The paper provides information on hydrodynamic and lithodynamic characteristics of processes in the Caspian Sea. A description of applied hydrodynamic models is presented. The numerical simulation of circulation, wave and lithodynamic conditions in the waters of the Northern Caspian Sea, middle and southern parts of the Caspian Sea was first conducted using composite computational grids. Simulated sediment transport results are presented. Results of numerical calculations of sediment accumulations in the second sweep of the Volga-Caspian canal are discussed. Materials and methods. Numerical modeling of coastal wave and hydrodynamic processes is performed using the Delft3d morphodynamic computer model. The Delft3D wave module includes a SWAN (Simulating Waves Nearshore) model for calculating the propagation and generation of waves. The hydrodynamic flow is simulated using the FLOW module, that solves non-stationary hydrodynamic equations and has a sediment transfer unit. Results. Computational grids are generated; they have a large step equal to 5,000 m. One grid is built for the middle and southern parts of the Caspian Sea and the other is made for the Northern Caspian; the grid step is equal to 1,000 m. The height and direction of significant waves in the Northern Caspian are provided. Sediment flows, averaged over 210 days in the SC, are provided. The authors also provide graphs of cumulative accumulation/erosion in the second sweep of the Volga-Caspian canal. Conclusions. The authors show that the average yearly shore-parallel sediment flow in the area of the marine edge of the Volga river delta has a southwesterly direction, and an estimate of its magnitude is provided. An assessment of sediment accumulation in the Volga-Caspian canal is made, and its results are compared with the data obtained in the course of dredging works.