It has been suggested that the Thames Tunnel is intended to ‘stop some sewage flowing into the river when it rains heavily’. In fact, the problem is more serious than that.
The Thames Tunnel is actually intended to capture almost all of the 39 million tonnes of untreated sewage that pours into the river in an average year. These discharges take place once a week on average and they can be triggered by as little as 2mm of rain. The largest discharges would fill an Olympic swimming pool in a couple of minutes.
It is a sizeable problem and if it isn’t tackled now it will get steadily worse. The question is how can this be done most efficiently and at least cost to bill payers.
Studies of various options go back to at least 2001 and they have all been looked at carefully by a wide range of experts. Many of the alternatives to a storage and transfer tunnel, such as sustainable drainage, green roofs, off-line storage and permeable surfaces have an important part to play in new developments, to avoid adding to the existing problems. That is why we have supported the inclusion of all these measures in the London Plan. But they are not sufficient to cope with the sheer volume of the existing discharges, in a highly developed and crowded city.
London’s first sewage ‘system’ was developed two hundred years ago by turning much of the natural drainage of the London basin into sewers. Reversing that process now would involve building a new sewerage system and could only be achieved at astronomical cost and disruption.
That is presumably why the coalition Government, in announcing their support for the Thames Tunnel described it as ‘…. by far the most cost-effective solution to the unacceptable problem of raw sewage being regularly discharged into the Thames.’ The same statement also said that ‘Defra and Ofwat will continue to scrutinise the costs and options to ensure that Thames Water’s proposals represent proper value for money.’
We have just launched a 14-week public consultation on the route of, and need for, the Thames Tunnel. This process will allow alternative schemes to be put forward and assessed alongside the currently preferred option.
More detail is available here about the three proposed route options for the tunnel, our video about tackling sewage in the Thames, where our public meetings will be held and how to provide feedback.
It is also important to recognise that the proposed Thames Tunnel will be the third of three important projects to deal with problems of sewage in the Thames: we have just started major upgrades, costing £675m, at London’s five major sewage works and building the £635m, four-mile Lee Tunnel in east London, to capture overflows to the River Lee and convey them for treatment at Beckton sewage works.
The proposed Thames Tunnel is the third and most challenging piece of the overall plan. It will build on the Victorians’ legacy, enabling us to leave the River Thames cleaner than when we inherited it. We believe it is the most appropriate and cost-efficient way of tackling the problem of sewage entering the Thames, as well as being fundamental to the economic andsocial wellbeing of this magnificent city both now and in future.
Richard Aylard is director of external affairs and sustainability at Thames Water
