A number of papers have been published in the academic press which describe the operations and mechanisms of the CatchIS system and its constituent models. The references below are those most relevant.

Brown, C.D. & Hollis, J.M. (1996). SWAT - A semi-empirical model to predict concentrations of pesticides entering surface waters from agricultural land. Pesticide Science 47, 41-50.
This paper describes the development and testing against measured field data of the CatchIS pesticide 'HOTSPOTS' model, UK SWAT. The model predicts concentrations of pesticide in drainage from fields impacting on adjacent surface water bodies.

Hollis, J.M. & Brown, C.D. (1996). A catchment-scale model for pesticides in surface waters. In: The Environmental Fate of Xenobiotics. Proceedings X Symposium on Pesticide Chemistry, (Eds. A.A.M. Del Re, E. Capri, S.P. Evans & M. Trevisian) Universita Cattolica del Sacro Cuore, Piacenza, Italy), pp. 378 - 379.
This paper describes the development and initial evaluation of the CatchIS pesticide surface water catchment-scale model, SWATCATCH. The model predicts a weekly time series of peak and mean pesticide concentrations in stream / river water at a catchment outlet.

Brown, C.D., Bellamy, P. H. & Dubus, I. G. (2002). Prediction of pesticide concentrations in rivers in the UK. Pest Management Sci.58:363-373
This paper describes a comprehensive national evaluation of predictions from the CatchIS pesticide surface water catchment-scale model, SWATCATCH. The evaluation was carried out on behalf of the UK Environment Agency, who now use the model as part of their Decision Support Tool for assessing the impact of agriculture on the aquatic environment.

Holman, I.P., Dubus, I.G., Hollis, J.M. and Brown, C.D . (2004). Using a linked soil model emulator and unsaturated zone leaching model to account for preferential flow when assessing the spatially distributed risk of pesticide leaching to groundwater in England and Wales. Science of the Total Environment, 318 (1-3), 73-88.
This paper describes the development and initial evaluation of the CatchIS pesticide groundwater leaching model (as part of the EA's POPPIE programme), which combines a meta-model of the MACRO soil leaching model (which accounts for the effects of pesticide losses through preferential or by-pass flow) with the AQUAT subsoil leaching model. The model predicts concentrations of pesticides impacting on groundwater bodies within a 2 km x 2 km grid across England and Wales.

Hallett, S.H. (2006) "CatchIS: A Catchment Information System. An environmental management information system for catchment managers. Water Active Magazine (www.wateractive.com) p8."