Benchmark models for diffuse pollution: the challenges
Dunn, S. M.; Dilks, C. F.
Successful management of diffuse pollution is seen as being an essential factor in achieving the objectives of the EU Water Framework Directive (WFD). The application of numerical models for diffuse pollution is likely to play a key role in the development of River Basin Management Plans designed to achieve the targets of the WFD. Given the extensive range of situations and potential applications for diffuse pollution models, it is important that model users select tools that are appropriate to their application needs. There are many potential sources of uncertainty in diffuse pollution models that can be categorized as input data and parameter uncertainty, model structural uncertainty and validation data uncertainty. Some examples of uncertainties that may be significant in evaluating catchment response to management changes are discussed. The EC 5th Framework project Benchmark Models for the Water Framework Directive has developed a model evaluation tool (MET) to guide policy makers and modellers towards selection of appropriate model codes, through consideration of their model application needs and by highlighting a range of potential issues relating to model functionality. A case study application of the Soil and Water Assessment Tool (SWAT) has been applied to the Ythan catchment in NE Scotland, to demonstrate and evaluate the utility of the MET. The findings of the SWAT application are critically discussed in relation to the utility of the MET and challenges of diffuse pollution modelling in general. It is concluded that significant developments of diffuse pollution models are still necessary if they are to prove of value in the river basin management planning phase of implementation of the WFD. It is proposed that an appropriate way forward for catchment modelling may be to utilize a range of models focused on different aspects of the system with results from the different models loosely chained to provide an overarching representation of the system behaviour.