Thames Water is on track to deliver the UK’s biggest sustainable drainage system (SuDS), despite the challenges of working across several developers’ sites at Nine Elms.
The Nine Elms development on the South Bank in London is set to have 22,000 apartments once complete, along with several hotels, restaurants and office spaces.
In 2014 it was decided that an existing combined sewer at the development, designed by Victorian engineer Joseph Bazalgette, would not cope with the extra waste water generated. The decision was made once progress had already been made at several of the sites, including the US embassy building.
An integrated water management study was carried out by Thames Water in partnership with the Greater London Authority and the Nine Elms Partnership to see what could be done. After considering several options, including building an additional sewer, Thames Water decided to deliver an innovative £16M SuDS programme for the site as it was the least disruptive and most environmentally friendly choice.
Different types of eco-friendly drainage such as roof gardens, ditches with filtering vegetation and rain gardens will all help deal with wastewater in a sustainable way. Excess waste water will flow through a 900m pipe into a 10m wide and 10m deep pumping station, and out into the Thames; easing pressure on Bazalgette’s sewer, which will be used for foul waste only.
Thames Water’s Eight2O alliance is responsible for constructing the scheme under its CABV joint venture, made up of Costain, Atkins and Black & Veatch.
Although construction started in November 2016, the drainage scheme is still set to become operational in October this year and to fully finish in December.
But Thames Water does not control the area where the pipe will be constructed: it travels through several active sites, which are all run by different developers and at different stages of construction. As a result, the team has had to work around obstacles out of their control.
“The biggest challenge on the job has been the combination of all the different land owners,” said Eight2O project manager Paul Clough.
It has meant working closely with other developers at Nine Elms to avoid construction clashes. The drainage system travels through a Royal Mail development site, which is in the early stages of construction; it will eventually house more than 2,000 units, retail spaces and a primary school.
Contamination from a gas works, which had occupied the site remains in the ground. Royal Mail’s contractor is now laying the new infrastructure for the development such as roads and sewers, but has also been removing and cleaning contaminated ground at depths of 2m to 4m for around 18 months. The development will eventually be separated from the contaminated ground by a membrane, which is in the final stage of design.
Thames Water’s drainage pipe had to be dug at the same location, between 4m to 5m deep, after the top 2m of contaminated ground had already been cleaned. It meant the pipe would run through contaminated ground, and as a result the team has had to work closely with the contractor to avoid recontamination. They have also been working together on the best products for the pipe and backfill, as some of the contamination could cause corrosion damage to the pipe and its joints.
Collaboration has been vital in ensuring the scheme has stayed on track: at the neighbouring US embassy site, security issues meant plans for the building could not be shared with Eight2O.
“My key learning point would be early engagement,” said Clough, adding that it was vital to understand each of the parties’ different constraints, and their expectations of the SuDS project.