Southern launches pilot to cut CSO discharges with wetlands

Southern Water has begun a pilot in West Sussex to reduce the use of combined sewer overflows with nature-based solutions.

The work at Bosham, which is adjacent to Chichester Harbour where the company has created a dedicated taskforce to improve water quality, is intended to alleviate the currently overloaded network.

A wetland scheme is being built, due to complete in 2027, at the Bosham wastewater treatment plant. Elsewhere Southern will reline and seal 10km of sewer, and seal private pipes to reduce infiltration into the sewer network.

The pilot scheme follows Southern getting the green light from government last month to accelerate £10 million of investment over the next year to tackle storm overflows.

It is directing £10 million into real-time digital wastewater catchment control, accelerating its Chichester Harbour wetland scheme and managing surface water.

Chichester Harbour has proved a challenging area for the water company. Its deteriorating water quality has been blamed on Southern, which in turn has pointed to myriad pollution sources causing damage to the area. An action plan has been agreed upon between the water company and stakeholders to recover the environmental status of the harbour.

Southern’s taskforce lead Joff Edevane said: “We’re really excited to begin work on another pilot that will make a real difference to reducing storm overflows in and around Chichester Harbour.

“We know that this area of our region suffers with significant groundwater challenges, so we are keen to employ a mixture of approaches that have proven successful elsewhere to tackle this problem and reduce storm overflows. We are looking forward to working closely with the local community during these efforts, for the benefit of customers and the local environment.”

Southern’s plan to drive down the number of discharges from storm overflows across its region includes optimising sewer networks and treatment plants with sensors and monitors as well as nature-based solutions.

Its Clean Rivers and Seas taskforce has outlined £1.5 billion of investment to be carried out in the 10 years to 2035. At PR24, the company has proposed spending £682 million to reduce the use of storm overflows by 40% by 2030 at 179 priority locations.

It plans to cut overall pollution incidents by half and eliminate serious events by installing new mains and increasing power resilience at pumping stations as well as adding monitoring across wastewater networks. The plan, submitted to Ofwat in October 2023, specifies spending £600 million on upgrading 38 sewage works to meet statutory nutrient requirements.