SHETRAN is continually evolving as improved process descriptions become available, as more efficient solution schemes are developed and as increasing computing power opens up new opportunities for software development and for the range and scale of model applications. Areas likely to receive attention in the future include:
1) New or improved process models, e.g. for channel bank erosion and infiltration of fine sediments into channel beds of coarser material. Further research is required into the evaluation of the soil erodibility coefficients as a function of measurable soil properties. Overland flow sediment transport is also a poorly researched area where improved process equations are needed.
2) Improved user-friendliness. The current versions of SHETRAN are run on Unix-based workstations. Combined with the model’s complexity, this makes it difficult to place the model in the public domain. However, a user-friendly front-end has already been added to help new users and a PC version is under development. In the future SHETRAN will therefore become more generally available.
3 ) Tests and applications. Each new development requires testing; currently, for example, the landslide and gully erosion and sediment yield components are undergoing validation at test sites. Such tests may require field programmes to provide the necessary data. Future applications are likely to concern the impacts of climate and land use change on erosion and sediment yield. Applications at the larger basin scales will require supporting research on scale dependencies. Related to this, there is a need to investigate, and minimize, the uncertainties in model parameter evaluation. SHETRAN has already been integrated with ecological and economic models within decision support systems and such integration is likely to continue in the future. In particular it enables feedback between the physical and other domains to be accounted for in modelling basin response.
Acknowledgements SHETRAN’s development and application at the Water Resource Systems Research Laboratory (WRSRL) has been carried out over many years by a large team of research staff under the overall leadership of Professor P. E. O’Connell (WRSRL Director) and Dr. J. Ewen. Their work forms a basis for some of the discussion in this chapter and its contribution is acknowledged by appropriate references in the text. Particular thanks for help with the diagrams are due to Mr R. Adams, Dr S. J. Birkinshaw, Mr A.
Burton and Mr J. Sheffield. Financial support for SHETRAN erosion modelling has been provided by the Commission of the European Communities, UK Nirex Ltd, the UK Department for International Development and the North Atlantic Treaty Organization.
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