Modeling of tides and spreading of saline water in the Arabian Gulf and in the coastal area of Abu Dhabi with a flexible mesh model

Abstract

The coastal area of Abu Dhabi is characterized by a complex network of tidal channels and shoals. This area is rapidly evolving, and the increasing amount of desalination plants to provide the growing population with fresh water can have large consequences for the local ecology through the emission of highly saline water. In this study, tidal motion and the spreading of salt released by desalination plants in the Abu Dhabi area and the adjacent Arabian Gulf are investigated with the help of several numerical models, which use either a conventional curvilinear or an unstructured (finite volume) grid. The software that was used for modelling with unstructured grids (D-Flow FM) is still under development. Therefore this software is compared to conventional software as well.

In the first part of this study, the Arabian Gulf is represented as a rectangular basin, for which an analytical solution is available (Taylor, 1920). Different numerical models, which employ curvilinear and unstructured grids, have subsequently been used to simulate tides for that same idealized configuration. It was found that both Delft3D and D-Flow FM compare well and that they simulate overall tidal propagation patterns well.

In the second part, numerical models (using structured and unstructured grids) are discussed that simulate the Arabian Gulf using realistic coastlines and bathymetry. All models compare well to observations, and D-Flow FM has been found to be suitable for building a detailed model of the coastal waters around Abu Dhabi.

In the third and last part the fine-resolution, unstructured grid model around the area of Abu Dhabi is used to describe the spreading of highly saline water discharged by desalination plants. The results indicate that the effect of a single desalination plant is widespread. Close to a desalination plant a dynamic salinity equilibrium is reached approximately 2 months after the desalination plant started to emit brine. The flushing time and the residence time of salt have been computed for a channel neighboring a desalination plant. The total salt transport is separated in a mean and fluctuating part and fluctuations in salinity and water transport are found to be dominant at locations where the bathymetry or coastline varies strongly.