Managing urban flooding remains one of the key challenges for the operators of sewerage systems in the developed world. In the UK it has been an important area of investment over the last five-year asset management period, and will be even higher on the agenda for the next five. Although modern software tools are extremely sophisticated in estimating the probability of sewer surcharging and surface flooding, the science of assessing individual property flood risk is still in its infancy.

The authors have developed a flood risk tool to identify the consequential effects of sewer system overloading in terms of individual property flood risk. This is post-processing software using the output from conventional modelling software. The tool recognises two separate causes of property flooding: backing up flow through connecting drains when sewers are surcharged, and the conveyance of flood flows over the surface. The severity of each is combined with return period to give a flood risk score for each property within a catchment.

The tool has been trialled by UK water companies as a proactive way of managing flood risk and has been shown to offer significant advantages over traditional methods of urban flood management.

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