Table of Contents Section headings and selected papers: Foreword. Principles of Modelling. Principles of modelling, M B Beck. Designing experiments for model identification of the nitrification process, P J Ossenbruggen et al. Investigation of a new approach to predict water quality extremes with a case study of chemical determinands in stream water, A J Jakeman et al. Optimizing water quality modeling in an uncertain environment, J J Warwick. Policy and Planning. Application of systems analysis in water pollution control: perspectives for Central and Eastern Europe, L Somlyody. The development of best optimum solutions to drainage problems, R M Ashley & M J Goodison. Development of a personal computer-based system to support basin-wide management of water quality in lakes and rivers, M Okada et al. Operations and Control. A network algorithm for the optimum operation of urban drainage systems, K Neugebauer et al. Optimization of the operation of the oxidation ditch process incorporating a dynamic model, M von Sperling & J P Lumbers. Stochastic control of the activated sludge process, J C Kabouris & A P Georgakakos. New Technologies and Expert Systems. CORMIX: an expert system for mixing zone analysis, G H Jirka et al. Rule-based expert systems in the control of wastewater treatment systems, R Laukkanen & J Pursiainen. Aspects of intelligent tutoring systems applied to small water treatment plant expert systems, A G Collins et al. Appendix A. DBAPE - A database and model parameter analysis system for agricultural soils to support water quality management, J C Imhoff et al. Appendix B.Computer demonstrations. Index.