The importance of three dimensional modelling in enclosed coastal waters as demonstrated by circulation patterns in manila bay, Philippines

Flow processes found in Manila Bay, Philippines are dominated by wind driven currents. Flow circulation within the bay has a significant impact upon the water quality and sediment transport processes occurring in the bay. This paper presents the outcomes of a study, funded by the International Atomic Energy Agency, which used a combination of field data collection and numerical modelling techniques to assess the distribution of Red Tide algal blooms within Manila Bay. Model verification against nuclear tracer experiments was undertaken for a three dimensional hydrodynamics of Manila Bay. Field experiments were undertaken using radioactive isotope tracers to track flow currents at selected locations in the bay. The data from the field experiments were used to validate a three-dimensional hydrodynamic (RMA-10) model at locations within the bay. This data was used to determine the horizontal and vertical diffusivity as well as the variations - surface flow and flow at depth. The outcomes of the field data collection and numerical modelling work clearly demonstrate the importance of using three-dimensional flow modelling in defining the hydrodynamic behaviour of the bay. The significance of wind generated currents and the resulting three-dimensional flow patterns is indicated by both field data and model results. A comparison against model results obtained using a two-dimensional depth-averaged flow approximation is presented to further highlight this point. Scenarios of red tide movement within the bay using a three dimensional random walk transport model (3DRWALK). These also highlight the importance of three dimensional upwelling in downwelling processes.