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In the UK, and many other parts of the world, combined sewer systems are used, in which surface run-off mixes with foul sewer water.

During heavy rainfall, sewers may exceed capacity, causing diluted wastewater to be discharged from combined sewer overflows into rivers, or even cause flooding. Wastewater contains contaminants, parasites, bacteria and viruses.

Contamination of urban areas from combined sewer overflows or surcharged sewers (where water backs up in the sewer) during extreme events represents a serious, growing health risk for urban residents.

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Manholes create changes in shape and direction, leading to non‐uniform flow paths.

Professor Ian Guymer

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Standard 1D advection-diffusion equation model performance degrades when the underlying assumptions are not met. In the case of manholes, their highly irregular shapes differ from the assumption of a uniform cross-section. This often leads to under predictions of peak concentrations.

Research at the University of ��«Ӱҵ has shown that within manholes, mixing conditions vary depending on manhole surcharge level (Guymer and Stovin, 2011).

Guymer et al. (2020) recently published over 4,500 dye traces across more than 1,100 manhole configurations carried out at the University, along with residence time distributions to describe the fundamental mixing processes.

With this knowledge, a new compartmental model has been developed to better predict water quality in combined sewers, which can be used to reduce risk to both humans and the environment.

Relevant articles and projects

• Guymer, I. and Stovin, V. (2011). . Journal of Hydraulic Engineering, 137(10), 1160-1172.
• Guymer, I., Stovin, V., O'Brien, R., Dennis, P., Saiyudthong, C., Lau, S.-T. D., and Sonnenwald, F. (2020). 
• CENTAUR Project