Accommodating the permanent structures required to operate the tunnel.

The multi-billion project to reduce sewage overflow into the Thames will involve construction in two sites along the river in and around Putney. The consultation documents were released today and include a proposal for a worksite to connect the local combined sewer overflow (CSO), known as the Putney Bridge, to the main tunnel of the proposed Thames Tunnel project and one on Barn Elms Sports Grounds.

In their consultation document Thames Water states:
" We need a significant number of sites in order to construct the Thames Tunnel project. Large ‘shaft sites’ are required at certain points along the route to allow the construction of the main tunnel. Smaller ‘CSO sites’ are also required near each of the most polluting CSOs to connect them to the main tunnel."

They continue:
"We shortlisted four possible work sites on the foreshore close to where the CSO discharges under Putney Bridge. The configuration of the existing drainage network and the high density of local buildings meant the only viable CSO interception locations are within the foreshore of the river and
therefore all of the sites are located within the Putney
Embankment Conservation Area. We assessed the suitability of each site by taking into account engineering, planning, environment, property and community considerations. From this process we identified our preferred location as the foreshore site immediately to the west of Putney Bridge.

Shortlisted sites:
Site 1 – Foreshore, end of Brewhouse Lane and
Site 2 – Foreshore, adjacent to Putney Bridge and St Mary’s Church.
Both sites located to the east of Putney Bridge would be adjacent to the Grade II* listed St Mary’s Church, The Boathouse public house and the riverside walkway.
Use of site 2 could have a greater impact upon the residential and commercial properties at Putney Wharf Tower. These residents would be in closer proximity to the works and would not benefit from the highway separation that exists between sites west of Putney Bridge and the associated adjacent residents.
Site 3 – Junction of Lower Richmond Road and Putney Embankment
This site is considered the less suitable of the two sites west of Putney Bridge. It is located further away from the CSO discharge point beneath Putney Bridge and would therefore require increased construction in the foreshore. The reduced clearance of the site to adjacent amenities could cause greater disturbance to residential properties and commercial buildings on
Lower Richmond Road and the bars and restaurants on Putney Embankment.

Site 4 - Their preferred site is at Putney Bridge Foreshore
Their preference according to their consultation document :
" Compared to the alternatives, the buffer provided by the road has the potential to reduce the impact of the construction works on the nearest residential and business premises and users of the Thames Path. The shaft site is located further away from Grade II listed Putney
Bridge and Grade II* listed St Mary’s Church than two of the alternatives considered. It is also relatively close to where the CSO currently overflows into the River Thames. This preferred site would also provide greater separation between the working area and the Putney Bridge Pier to the west, thereby minimising the impact of the works upon vessel movements and navigation to and from the pier."

The CSO itself is located within the southern supporting arch of Putney Bridge, all the possible
work sites would require works beneath the arch and against the structure of the listed Putney Bridge. Access from the local road network is possible but, due to the space constraints, limitations would need to be imposed on the size of vehicles that can get to the site.

Thames Water indicate that the location as a construction site would be required for approximately two years. It would then be vacated as much as possible but a smaller area kept
secure for subsequent equipment installation.  They propose that the construction traffic would enter and leave the site at the location of the existing slipway to reach Lower Richmond Road.
As the site would be located in the foreshore we would need to construct a temporary cofferdam around it to protect the works from the river.

Their plans include some above-ground structures on this site after the construction work has finished -  they propose to extend the existing river wall to create a new area of hard-standing. With a new, realigned, slipway will be constructed as part of the work.  The structures to be located on this new area would include a ventilation column (approximately 10m high and 1m diameter), along with a rectangular kiosk (approximately 1.5m high, 1m wide and 3.5m long)
housing electrical and control equipment.   They would leave the area around these structures as hard-standing to allow vehicle and pedestrian access to this new area of river frontage and the relocated slipway.

Barn Elms is the preferred site to connect the local combined sewer overflow (CSO), known as the West Putney Storm Relief Sewer, to the main tunnel.In teh consultation document they state it is the preferred site because:
"This allows us to combine the works for the construction of the main tunnel with those required to connect to the local CSO, sited on Beverley Brook. Combining all the works in one location would help reduce the overall impacts. As the Barn Elms sports fields site is a very large
area, our work site would only occupy a part of the south-eastern corner of the site, adjacent to the river.  While this would temporarily disrupt the use of the sports pitches in this area, and will have some effect on recreational river users, we believe our proposed works can be positioned to minimise this disruption. We also believe we can provide suitable mitigation for
the potential impacts on the rowing and sailing club and the scout hut and community hall located on the eastern boundary of our proposed site."

Two other sites had been investigated; Leader Gardens & the boat worskshop on eth Embankment beside Leader Gardens, but they are more residential adn Thames Water believe Barn Elms would:
"... reduce potential impacts of construction on the surrounding community and minimise any impact on the Putney Embankment Conservation Area. The site would allow good vehicular access to the local road network. We are currently considering two route options. Option 1
would be a new dedicated route along the southern perimeter of the sports field and connect to Rocks Lane. Option 2 would be to share the existing access passing through the sports field and connect to Queen Elizabeth Walk. Option 2 would require a local extension of the existing access route between the Boat House facility and our proposed site. The access options are illustrated on the plan on the previous page. These options would avoid the general issues associated with routing construction traffic through narrow residential streets or the Putney Embankment Conservation Area to the south of the site."

Thames Water will need to build a 25m-diameter circular shaft big enough to put the machine used to dig this section of the main tunnel into the ground and remove the excavated material.

Permanent use of the site - Thames Water will propose above-ground structures on this site after the construction work is finished. Most likely a ventilation column (approximately 15m high and 3m diameter) and a building (approximately 10m high, 12m wide and 20m long) to provide ventilation and filtering of the air in the tunnel.
Thames Water state that:
" We would leave the area around these structures as hard-standing to allow vehicle and pedestrian access for maintenance. We could soften this with appropriate landscaping.
Above is an example of how the site could look after construction has finished. As part of our public consultation we would like to know your views on the permanent look and use of the site.

September 10, 2010