Modelling catchment-scale nutrient transport to watercourses in the UK

Water resource managers require catchment-scale nutrient transport models t o help in the investigation and control of diffuse pollution. Many differen t models exist for water and pollutant movement, causing problems of select ion because each model has often been constructed for specific purposes, an d the choice of an appropriate one is difficult: wrongly applied models can lead to unreliable results and misleading information. The selection of a model for estimating phosphorus loss from a lowland English catchment is de scribed. 14 models, whose underlying principles had been published, were ev aluated. 'SWAT' was found to be the most suitable. It has several favourabl e qualities, but also several shortfalls which may impair its predictive ab ility. Their identification enables the model code to be re-written. Reliab ility estimation is needed to ensure that the ranges of model prediction ar e known.