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Understanding drainage capacity for the 21st Century

Posted: 07-Aug-2018
How much capacity is available in the UK's drainage systems now? What capacity might be available in the future? And what investment will be needed in the long term?

The expansion of our towns and cities, resulting in fewer green spaces to absorb rain, combined with more unpredictable weather due to climate change, make it essential to ensure the resilience and sustainability of our drainage infrastructure in the future. On behalf of the Water UK led 21st Century Drainage Programme, HR Wallingford has produced the first National Picture of available capacity in the UK’s foul and combined sewerage systems. 

The vision of the 21st Century Drainage Programme is to enable the UK water industry, in partnership with the UK’s governments and regulators, to take action now that will ensure the resilience and sustainability of the UK's drainage systems. This project has focused on understanding the available capacity in the UK’s foul and combined drainage systems to accommodate present-day flows and flows expected in the future, reflecting changes in population, urbanisation and climate. 

The first phase of work resulted in The 21st Century Drainage Programme Capacity Assessment Framework. This is a consistent, transparent and high-level approach to assess how much capacity is available in drainage systems now, what capacity might be available in the future, and the investment needed in the long term. The initial framework focused on capacity in the foul and combined sewer network, but with the potential to be extended to surface water sewers. 

The second phase of work involved HR Wallingford supporting the 12 UK sewerage companies in putting the new framework into practice, and producing a first National Picture of available drainage capacity. 

Helen Udale-Clarke, Project Manager for HR Wallingford, said: “This is only the first step for the industry in being able to share a common understanding of drainage capacity. But it is a significant one. Never before has it been possible to show information at a national scale like this. We have also learnt a great deal from this process, which will feed into future use of the Capacity Assessment Framework.”

Better information about surface water drainage

The third phase of work investigated the potential for the Capacity Assessment Framework also being used to assess the capacity of surface water drainage assets, focusing on surface water sewers owned by the UK’s sewerage undertakers. Typically, surface water drainage assets in any particular area are owned by a number of risk management authorities who may have different ways of monitoring and measuring their performance, as well as varying degrees of information about these assets. Having better and more consistent information about surface water drainage across asset owners would improve understanding of the risks associated with these assets.

Co-funded by Defra and Water UK, and referred to in Defra’s Surface Water Management Action Plan, this research has identified that the Capacity Assessment Framework has the potential to achieve a better understanding of surface water capacity.

Full details of the framework approach, the results from the assessment of the present day available capacity of the UK’s foul and combined sewer networks, and HR Wallingford’s report on the trial using the framework to assess the capacity of surface water sewers are available to download from Water UK’s website.
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