Integrated water modelling and management for bathing water compliance

Due to the increasing cultural and economic benefits of bathing waters and the shellfish industry in the UK, water quality in estuarine and coastal waters has attracted considerable public attention in recent years. However, some bathing beaches have had to be closed on various occasions because the Faecal Indicator Organism (FIO) levels exceeded the minimum mandatory standard. The relationships between faecal bacteria sources in the upstream catchment and the bathing water quality are complex, since multiple processes and driving factors affect the transport and fate of FIOs through the basin. To obtain accurate FIO predictions and better management of bathing water compliance, for a changing environment and more stringent standards, it is necessary to build an integrated modelling system which includes comprehensive dynamic faecal processes from catchments, gullies, pipes, tanks, river networks etc., through to the estuarine and coastal waters. In the paper, details are given of the development of such an integrated numerical model for simulating the transport and dynamic decay processes of FIOs from a catchment region to the coast. The model is used to predict the distribution of FIO concentrations in the bathing waters near Blackpool, which is one of the most popular bathing resorts in the UK. Furthermore, its bathing water quality is governed by multiple faecal sources in the catchments, with different land uses and some highly urbanised regions. In addition, the FIO transformation processes in the riverine and estuarine waters are driven by: tidal currents, wind induced waves, inflow and faecal discharges, unsteady sediment transport etc., and are included in the integrated model by linking a number of processes within a modified EFDC 2-D model. The extensive measured and statistical data from the catchments, river networks, CSOs, WwTWs discharges and estuaries have been collected for determining various model parameters, and for calibration and validation of the integrated model. Model predictions are used to assess the impact of different concentrations and locations of FIOs on the bathing water quality, with the aim being to provide information for deriving more effective management strategies to meet the new EU standards, to be implemented in 2105