CSO legislation derailed water company drainage and wastewater plans

Water companies were forced to rip up their Drainage and wastewater management plans (DWMPs) just weeks before they were due to be finalised, after the government introduced last-minute rule changes around combined sewer overflows (CSOs).

Speaking at the Utility Week WWT Wastewater conference, Northumbrian Water’s sustainable drainage manager Richard Woodhouse said years of work was effectively thrown out the window after the government released its Storm overflows discharge reduction plan, leaving the firm with just six weeks to revise its plans.

The last-minute legislation added requirements for the first time for companies to deal with individual combined sewer overflows (CSOs), which had to rapidly be incorporated into plans.

He described the DWMP journey as “quite long and quite challenging” as plans had to adapt overtime, however the legislation was the biggest change.

“That came out just three months before our draft was due to be published,” Woodhouse said. “We were instructed to include those targets in our draft plan. We had been working on a catchment based approach for a number of years and we literally had six weeks to change everything, so that’s what we did.”

This limited timeframe to incorporate the legally-binding expectations forced a move away from a risk-based, best-value approach for each drainage area to an individual asset approach, and a shift away from catchment-wide solutions.

Defra’s Storm overflow reduction plan called for an 80% reduction in discharges by 2050 in its discharge reduction plan. It said companies should prioritise CSOs in sensitive catchments and eliminate risks from 3000 sites by 2035.

This move to end of pipe rather than holistic was, by necessity, reliant on grey engineering solutions instead of multi-capital approaches at catchment level and nature-based solutions.

Reflecting on the nature-based solutions in Northumbrian’s DWMP, Woodhouse said he was disappointed that blue-green solutions were very expensive and were therefore not more widely opted for in the plan.

He explained Northumbrian had created a catchment-wide approach in its DWMP for each part of its region, however some of these were prohibitively expensive compared to adding storage and end of pipe solutions.

This was exacerbated for work to tackle CSOs, Woodhouse said, when the legislation from Defra resulted in a lot of last minute additions and changes that would not have been the company’s first choice.

The company was given feedback on its draft plan that said it needed more short-term detail. “We had to shift from long-term planning to short term detail,” Woodhouse added. “We were told our DWMP and PR24 planning should match.”

Chris Walters, senior director of price control at Ofwat, also expressed disappointment that DWMPs had not featured a higher proportion of nature-based solutions.

He said the regulator had hoped to see more of a shift away from traditional grey engineering towards blue-green infrastructure in plans.

Speaking on the same panel, Clare Seymour, strategy implementation manager at Yorkshire Water defended the value of creating the DWMPs, even if they are not wholly adopted in 2025-30.

Seymour said if options were not picked up for 2024 business plans, they would be ready to be incorporated at the following price control (PR29).

Ofwat previously warned that environmental legislation due to be published by government this year would be required to be reflected in business plans.

Walters said at Utility Week Forum last month that companies should be prepared to change plans between the draft and final determinations to include new legislation.