Integrated water quality modelling: Application to the Ribble Basin, U.K.

Abstract

This paper reviews the traditional approach of linking models to cover integrated water management from the upper reaches of catchments through river basins, into estuaries and to the coastal/marine environment. It highlights some of the deficiencies in the approaches currently being adopted in many non-integrated studies, where artificial boundaries are included in the system, and then highlights the need for a more integrated conceptual approach. A case study is discussed, namely the non-compliance of bathing waters along the Fylde Coast and Ribble Basin (U.K.) from riverine inputs, with the inputs arising from Waste water Treatment Works (WwTW), outfalls and drainage systems. A more integrated approach was applied to this estuary, with refinements to the artificial boundaries. Both hydrodynamic and solute transport processes in 1-D and 2-D domains of this estuary were modelled for a wet event in June 1999. The bio-kinetic decay process representation included the impacts of salinity, solar irradiation, turbidity and water temperature on the decay rate. Solutes modelled included faecal coliform, water temperature and salinity. This paper demonstrates that a similar or better accuracy of the coliform concentrations can be achieved using an integrated model based on a realistic representation of physical and biochemical processes. This is significant because the integrated model does not need extensive calibration to give good results. This is therefore a much more robust model which is not influenced significantly by the position of boundaries. The robustness of the model gives increased confidence in predicted results for new scenarios where measured data is not available. This is particularly important for all types of real time water quality prediction (e.g. toxic spills) including bathing water quality. Hence better decisions can be made when considering investment strategies, appropriate for various treatment options and catchment management solutions in the river basin upstream.