Methods to accompany and evaluate planning of combined sewer overflow treatment concepts for complex sewer systems

Simulation tools are in common use to evaluate combined sewer overflow (CSO) treatment concepts in complex sewer systems. However, the planning of CSO structures in a sewer system is a matter of local constraints, expert knowledge and trial and error. Common standards only provide general recommendations to plan CSO structures and work out management strategies. Additionally, modelling the emissions of complex sewer systems tends to result in comprehensive findings. Although, it is essential to understand local behaviour and interaction of CSO structures in a system to improve local and overall performance there is a lack of tools to illustrate comprehensive simulation results in a simple way. In this context the methods presented here are developed. These include clear illustrations of the as-is state in the catchment using Sankey diagrams to show relevant volume and pollutant flows. Furthermore, loading and treatment indicators are suggested to illustrate local loading conditions and treatment capabilities of CSO structures in relation to the overall system. Additional emission indicators provide information on local emissions and show interactions of CSO structures. The results indicate that the suggested methods contribute to an efficient evaluation of interactions and performances to improve treatment strategies in the planning phase.