Southern Water is working in the Newnham Valley again to complete further improvements to its sewer network.
The company has invested £12 million during the past two years to survey and seal the sewers in 60 towns and villages prone to groundwater flooding and is spending a further £2 million this year. More than £1.5 million has been invested in improvements in the Newnham Valley alone.
When incessant rainfall occurs, the water table can rise to the surface causing groundwater flooding. This affects the sewer network as groundwater infiltrates it. Sewer manhole covers pop up and toilets back up, potentially causing releases of sewage into streets, gardens and properties. Without immediate action many communities cannot drain their domestic wastewater – including flushing toilets, taking baths and showers.
In the Newnham Valley Southern Water has surveyed over ten kilometres of sewer pipes and drains and 260 manholes, identifying where leaks were allowing groundwater into the system when the water table is high. Engineers have repaired 3.6 kilometres of sewers where infiltration was found.
Most of the repairs have been completed but the company returned to the Valley again in November to conduct repairs in Bishopsbourne and Bridge which will be completed in December.
The sewer serving Bourne Cottages (which, as its name suggests, is a terrace of seven cottages near a water course) in Bishopsbourne has been identified as a major contributor of groundwater to the sewer network so, after inspecting its length via CCTV cameras, repairs are being made.
In Brewery Lane in Bridge the 150mm diameter sewer has been invaded by various roots, causing several points of infiltration, including gushers which are substantial leaks. This sewer is being relined.
Said Phil Barker, Southern Water’s Director of Operations: “Of course, the performance of any sewer system can never be guaranteed due to ground movements, the invasion of tree roots and the like but we are confident that, after such a significant investment, the performance of the Newnham Valley sewer network will have been improved considerably should the winter that is nearly upon us prove to be wetter than usual.
“Indeed, groundwater levels at Little Bucket borehole peaked at 85 metres last winter. This was over three metres higher than the level at which we had to start overpumping in 2013/14.
“However, we did not need to over-pump at all in the Valley during the winter of 2014/15. That winter was not as wet as the record-breaking winter of 2013/14 but it was still a wetter than average winter, underlining that our investment in the local sewer network has improved its performance.
“Meanwhile, we have updated the Infiltration Reduction Plan (IRP) for the Valley which has been submitted to the Environment Agency (EA). IRPs were never heard of until the EA, in its Regulatory Position Statement, required water companies across the UK to publish plans which effectively set out their strategies for dealing with groundwater flooding of the sewer network. Southern Water has responded by publishing the first IRPs to be agreed by the EA in the UK. They now form the template for other water companies to follow.”
The company has also tightened its maintenance regimes and has made improvements to its pumping stations to make sure that, should groundwater enter the network, it can be got away as quickly as possible.
Concluded Phil Barker: “Naturally, we are hoping for a drier than usual winter during 2015/16, but if the elements conspire against us we’re confident that our ongoing investment in the sewer system will again stand us – and our customers - in good stead.”