Application of 3D Deterministic Model on Marine Beach Water Quality Management in Hong Kong, China

Bathing beaches are important marine resources for coastal cities like Hong Kong. Bacterial level (Escherichia coli, E. coli) is adopted as the key indicator of beach water quality. The prediction/forecast of marine beach water quality is always challenging due to the high variability of E. coli level affected by hydro-meteorological conditions. A 3D deterministic hydrodynamic model is developed and validated to provide daily water quality forecasting for Hong Kong marine beaches affected by submarine sewage discharge. The modelling system has been in operation for daily real-time forecast of beach water quality since August 2011. Field surveys are conducted in 2012 to provide data for continuous model validation and assimilation. Compared with the beach E. coli data during the bathing season (April-October) of 2012, the model achieves an overall accuracy of 70-80% in forecasting the compliance/exceedance of beach water quality standard. The 3D deterministic model has been most valuable in the interpretation of the complex variation of beach water quality. Model predictions show that beach water quality is in general better during sunny days with diurnal tide, consistent with field observations. The insights gained can be utilized in the optimization of sewage disinfection dosage and in emergency responses.