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Separation of stormwater ‘key to health of sewer networks'

Greater stormwater separation by utilities is the key to extending the life of sewers and ensuring the wastewater network remains effective, speakers agreed at WWT's Wastewater 2017 conference yesterday.

Faced with the twin challenges of climate change and population growth, water and sewerage companies can no longer afford to allow so much surface water to enter the wastewater network, where it overwhelms treatment infrastructure and leads to polluting discharges from combined sewer overflows (CSOs).   

“The use of our asset base is changing – foul water sewers are transferring more storm water than they were ever designed to do,” Nevil Muncaster, Director of Asset Management at Yorkshire Water, told the conference in Birmingham. “We’ve got to start thinking about separation, and not just treatment. Removing the storm water problem is the key to giving us more headroom on capacity.”

However tackling stormwater requires new models of collaboration. Along with the Environment Agency and local authorities, Yorkshire Water has contributed to Strategic Drainage Management Plans across its region. Better drainage in an area conveys multiple benefits - including a better environment and flood prevention as well as a more efficient wastewater service – and Muncaster said that to convey these benefits it requires a different conversation with stakeholders, where people were treated as ‘citizens’ rather than ‘customers’.

“Strategic drainage management planning is very much the future for our industry. SDMPs are the way we can have a different conversation where we can talk about those multiple benefits,” he said.

The conference heard a case study of stormwater separation in action from Dr Stephen Blockwell, Head of Strategic Investment Planning at Northern Ireland Water. He outlined how Northern Ireland Water was investing £5.2M in resilience measures around Belfast, which is subject to both tidal and pluvial flooding. The pilot programme is using a powerful GIS modelling tool to identify the sources of stormwater flows, potential ‘sinks’ where the water can flow away and pathways where the water could be taken from one to the other. In total, 55 possible projects had been identified under the pilot with solutions considered including green roofs, swales and bioretention.

“The tool gives us a standardized method we can use to identify the best opportunities to invest; it’s much better than placing dots on maps or just choosing sites where politicians would like us to spend money,” said Blockwell.

However, he added that some of the projects were more difficult to get off the ground than others: for example, drainage interventions around schools often met resistance from local stakeholders and issues over the timing of the work.

In a later conference session, Richard Woodhouse and Ellis Furlong of Northumbrian Water presented a case study in the utility’s collaborative work at Brunton Park in Tyneside, where the combined drainage solution arrived at with local stakeholders included a diversion of the River Ouseburn; this ultimately led to 100 properties being removed from the flood risk register.

WWT's Wastewater 2017 conference took place in Birmingham on January 31st and was sponsored by Tarmac and CDEnviro.

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