Industry experts have called for the prioritisation of work to better understand and remove surface water without it entering overburdened sewers as a key challenge of climate change resilience.
Speaking at the Westminster Forum on priorities for water infrastructure the chief executives of Northumbrian and Thames as well of the National Infrastructure Commission (NIC) outlined the pressures that surface water was placing on sewer networks, which leads to flooding risks.
The Department for Environment, Food and Rural Affairs (Defra) is considering implementing mandatory sustainable drainage through schedule 3 of the Flood and Water Management Act, which would put expectations on developers.
Sarah Bentley, Thames Water chief executive, said: “Developers will really need to think about what they are connecting the surface water to. Why is this so important? Just a small patio of 6×6 on a semi-detached house during rainfall can create as much surface water runoff as sewage from 100 homes.”
Heidi Mottram, chief executive of Northumbrian, added: “We need to get much better at managing surface water. We all need to work together to get substantial amounts of surface water out of our systems, because this will make the biggest difference.”
Bentley added: “It doesn’t make sense in 2022 to collect the water, use electricity to pump it to a treatment works and use chemicals that impact the environment to teat rain that is now contaminated with sewage.”
Instead Thames and others in the sector advocate for catchment working to understand where rainwater is getting into its sewage networks and preventing it.
James Heath, chief executive of the NIC, outlined approaches to manage surface water based on the work the commission is currently undertaking. It will publish a report in November, commissioned by Defra, with recommendations that will form a key part of the second National Infrastructure Assessment (NIA).
He said the study has shown surface water is the single biggest source of flooding in England, yet the least is known about it as a flood risk due to it being “a highly localised and complex risk to model.” This, Heath said, makes it difficult to design solutions.
Without intervention the problem will exacerbate due to the increasing regularity of heavier rain, aging drainage infrastructure and urban creep, the NIA found.
He noted that requirements to manage combined sewer overflows (CSOs) would “eat up a lot of industry investment” during the next few price review periods but said there are opportunities to reduce risks from CSOs and surface water flooding.
He said the work of the commission would focus on delivering flood risk management that better plans for, protects, responds to and helps people recover from surface water flooding.
“Our study is mainly looking at the plan-and-protect elements of resilience as this is where infrastructure, whether nature-based or engineered, has the biggest role to play. But we certainly don’t think that an effective flood management strategy equals protection,” Heath said.
Heath said surface water flooding should be treated as “a tolerable risk problem” rather than trying to eliminate it. Work should be taken to gauge what the scale and frequency of flooding was deemed acceptable by society and future policy should also consider what the appropriate solutions are based on cost-benefit analysis.
Heath explained the NIC was looking at measures to minimise the impact of new development by designing schemes to be climate resilient and exploring how to upgrade or retrofit existing assets.
He said the Commission was also examining how nature-based solutions can be used to hold back water and whether the current regulatory model sufficiently supports it.
The report will make recommendations about “the importance of achievable resilience standards for surface water flooding, and recommend timelines for implementation”. It will set out appropriate levels of investment and how costs might fall between bill payers and taxpayers as well as the best mixture of above and below ground solutions
He added it will “likely” make recommendations on governance of managing surface water flooding to overcome the current challenges of shared ownership and responsibilities for maintaining drainage systems and assets.
“Our study will offer a view on whether the current governance system is fit for purpose and, if not, how should it be reformed, building on the earlier work done in this areas. And, as part of this, consider whether the different parties have the right incentives to work effectively together,” Heath said.