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Deep Bay is located nearby Hong Kong, South China Sea. it is one of the most productive wetland characterized with a narrow navigation channel and large intertidal zones covered partially by mangroves. The environment of this bay has been facing a threat due to serious pollutions in the upstream and uncontrolled uses of the land for coastal development. 

An initial effort was made to develop a management model system of the Deep Bay by collaborating between the Ecosystem Dynamics Modeling Laboratory and Hong Kong EPA. The objectives of this pilot project are to assess the current environment status of the bay and predict the potential trend of the ecosystem variability in future. See figure on the right for the geometric location of Deep Bay. Click here to view the full size of the image.

The model system

The Deep Bay model was developed using the unstructured grid, finite-volume coastal ocean model (FVCOM). The computational domain is configured with the non-overlapped triangular grid that provides the accurate resolving of the irregular coastline and the slope of narrow navigation channel. The model includes a three dimensional, mass conservative wet/dry point treatment that is capable of simulating the flooding/drying process over the intertidal wetland.

Figure on the right: Horizontal grid of the Deep Bay model. Horizontal resolution varies from 27 m in the upstream creek to 1.7 km over the shelf.  11-sigma levels are specified in the vertical, which corresponds to a vertical resolution of less than 1 m in the most of the shallow area. Click here or figure on thr right to view the full size of the grid image. Green: island. Cyan: intertidal wetland.

In this initial pilot experiment, we drive the model using the tidal forcing at the open boundary. The tidal simulation results are validated by comparising with the tidal elevation data recorded at two stations on the coast. We also run the model with inclusion of river discharge.

Recently the Deep Bay model has been upgraded with the MPI parallization FVCOM code with capability of simulating variable wind/suface heat flux plus solar short-wave isolation, groundwater, precipitation via evaporation, suspended sediment transport and flexible biological model as well as water quality model. To get the updated information of this model, please contact Dr. Chen at c1chen@umassd.edu

Tidal simulation

The model was forced by the tidal forcing consisting of five major tidal constituents (M2, S2, N2, K1 and O1) at open boundary on the continental shelf. The M2 tidal animation is shown here for example of the tidal flushing process over the intertidal zone in the Deep Bay. To make the image viewable on the web resolution, the velocity vectors were selected in a given search radius. The real model resolution is much higher than this animation.

Click here or right image to view the full size of the animation.

Salinity simulation with river discharge

To test the model system, we ran the model with an annual river discharge under a tidal flushing condition. The initial condition of the salinity was specified as constant everywhere, so in this idealized case the salinity gradient was established only by tidal mixing between the freshwater and the ocean water. It should be noticed here that this model run is not for the realistic hydrographic condition. To simulate the realistic distribution of the saliity, one must re-run the model with the observed field of the salinity as the initial condition.

Click here or right image to view the full size of the animation

Particle tracking

An example of particle tracking is given in the animation shown on the right panel. Paricles were released nearby freshwater discharge sites and traced by the flow velocity. No random walk was considered in this particle tracking, so the trajectories of particles shown here are just the path caused by the advection with no inclusion of mixing.

 

Click here or right image to view the full size of the animation.

 

 


 

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