Modeling Coastal Environment Using Random Walk Method

Coastal areas are often locations for important cities and ports, where the economy develops rapidly with a high population density. The frequent human activities inevitably have an impact on the coastal environment. With the development of science and technology, human disturbance on the marine environment is growing more and more intensely with a wider range. To protect and improve the eco-environment of coastal waters, people need to understand the migration and transformation of pollutants in the water bodies and the self-purification capacity of water bodies. Based on the knowledge obtained, the policies and methods for preventing and controlling of the pollution of marine environment could be established.In this paper, the development history of Lagranian particle models was introduced firstly. Then Lagrangian particle models in atmosphere and water environment were reviewed, among which the advancement in coastal and ocean environment were investigated further. The advantages and disadvantages of Eulerian, Lagrangian and Eulerian-Lagrangian transport models were summerized and the scope of application for each was indicated. The concepts of water exchange and time scales in marine environment were breifly introduced. The merits and drawbacks of both Eulerian and Lagrangian methods for calculating water exchange matrix and time scales were discussed. In light of the objective of this study, random walk method was chosen as the numerical approach.The numerical scheme, boundary treatment, parameterization and postprocessing technology for simulating passive solute transport in coastal water were discussed in detail. This model was validated using typical analytical solutions. Based on the model for passive solute transport, the random walk model for suspended sediment transport was developed in this paper. The principle of the model was introduced and the main factors and parameterization for modeling deposition and erosion were discussed detailed. The formular for calculating bed evolement was presented. The numerical results of the deposition and bed evolvement were in good agreement with the experiment data. The water exchange matrix generated based on the random walk model was interpretated physically and compared against that based on Eulerian model. The independent-labeled scheme for distinguish particles in simulation was proposed and the flexibility and timesaving of this method was analysed quantitatively by selected cases. Finally, the random walk model was applied to study the water exchange charatistics in Tianjin coastal waters, based on which the optimized region for constructing seawater desalination plants, the rationality of marine function zonation scheme was assessed and the management improvement was suggested accordingly.