The scope of integrated modelling: system boundaries, sub-systems, scales and disciplines

Integrated modelling has become an urgent issue of urban drainage and wastewater treatment planning. The scope of integrated modelling, system boundaries and disciplines to be involved are addressed in view of future developments and new paradigms in urban drainage, demanding the inclusion of the full urban water cycle. A system analysis is demonstrated to identify relevant sub-systems and components, processes and interactions within the urban water system. The permissibility to exclude subsystems or neglect interactions is evaluated. Integrated modelling of urban water system is characterised as an ambitious task in regard to system complexity, heterogeneous scales and interface problems. The methodical status quo is characterised in preliminary approaches towards integrated modelling. It is concluded that it does not seem promising to create and apply one entity model for the scope of integrated urban water modelling. Instead, the development of adequate and efficient IT frameworks is identified as the key issue of integrated modelling. Harmonising interfaces to facilitate the linking of existing models is presented as the objective of a European research project HarmonlT and the U.S. EPA Multimedia Integrated Modelling System project MIMS.