Advances in Water Treatment and Enviromental Management

RIBBLE ESTUARY WATER QUALITY IMPROVEMENTS 253environment at an economic cost. By combining hydraulic modelling of sewerage systems, bymeans of packages such as WASSP, with hydrodynamic and dispersion models of the receivingwater, it is possible to examine the range of options available in far greater detail than wasthe case previously. Provided both types of model are adequately validated against field data,the task of achieving the desired degree of compliance with receiving water standards becomesmuch more one of objective scientific investigation, rather than one based to a very largeextent on intuition and experience.CONCLUSIONSWhen putting forward proposals to improve water quality it is important that the cause of theproblem is sufficiently well understood, to enable the consequences of various possibleimprovement schemes to be properly evaluated.Mathematical models of the sewerage system and the receiving waters, used in conjunctionwith adequate investigative work, provide a powerful tool for illustrating the probableconsequences of various courses of action. Once it can be established that a number ofdifferent schemes will result in the degree of improvement initially required and, in mostcases, what would be required to achieve a greater improvement, the decision as to which isappropriate to any particular location will then involve weighing the costs of each optionagainst the immediate and future environmental benefits.ACKNOWLEDGEMENTThese investigations involved contributions from a number of people working for NWW andits consultants. The authors would like to thank them for their help in formulating the problemsto be addressed and evaluating possible solutions.REFERENCESCouncil of European Communities. 1976. Council Directive of 8 th December 1975 concerningthe quality of bathing water. (76/160/EEC) Official Journal of the European CommunitiesNo. L31, 1–7.Crawshaw, D H. 1988. Mathematical modelling of sewage dispersal and scientific studies.Appendix H. Fylde Coastal Bathing Water Improvements. Planning Study Final Report.North West Water, Warrington.Crawshaw, D H and Head, P C. 1989. Fylde Coast bathing water improvements environmentalinvestigations for the design of sea outfalls. In: Long Sea Outfalls. Thomas Tel ford,London, 75–88.Department of the Environment/National Water Council. 1983. The Wallingford Procedure.DoE/NWC Standing Technical Committee Report No. 28Head, P C, Crawshaw, D H and Rasaratnam, S K. In press. Fylde Coast bathing waterimprovements—storm water management for compliance with the Bathing WaterDirective. Proceedings of 2 nd Wageningen Conference—Urban Storm Water Quality andEcological Effects upon Receiving Waters. 20–22 September 1989. Pergamon Press,Oxford.