Barn Elms Reach - Thames Tideway Tunnel Putney Foreshore Embankment CSO Diversion/Activation

Mariners are advised that on or around the 6th January 2025 the Tideway Tunnel Project’s new Combined Sewer Overflow (CSO), and associated warning lights, at their site at Putney Foreshore Embankment will become operational. The old CSO outfalls beneath Putney Bridge will cease operation. 

After this date the CSO may discharge onto the foreshore and into the river whenever there is, or has recently been, a significant amount of rain in the local catchment area. The discharge amount and velocity will vary, but during a storm this could be up to 4 knots at low water, lessening the further from the outfall (example modelled flow velocities are included at the end of this Notice). 

The approximate location of the CSO at the Putney Embankment Foreshore site is shown in red on the chartlet below. 

A set of warning lights will be mounted vertically in front of a black backboard on the permanent works structure embankment wall above the CSO with a set of repeater lights mounted above. The location of the CSO warning lights are marked in yellow on the above chartlet.  

The lights will flash a yellow alternating 1 second pattern, visible by day and by night whenever the CSO is discharging or likely to discharge. 

Tideway advise the lights will activate a minimum of 3.5 minutes before any discharge will occur. 

All mariners are advised to exercise caution when passing the site, particularly over the slack water period (around two hours over low water and an hour over high water) if there has been heavy rain or if there is a Met Office weather warning for rain or storms in force for the London area and to pay attention to warnings given. The foreshore in the vicinity of the CSO should be avoided during these times. 

Further information on the characteristics of the CSO discharges, assessments of risk and potential impacts on mariners, which were undertaken by Tideway’s designers, are available on their website. Go to www.tideway.london/contact-us/document-library and follow the link to CSO DISCHARGES - RISK TO NAVIGATION. Mariners should consult these documents when passage planning. 

(This link will take you to a third-party website which does not belong to the Port of London of Authority and may have different security, privacy and accessibility standards).  

Example discharge plumes and velocities in m/sec for a typical year return period discharge 

(1 m/sec = 1.94 knots) 

Typical year return period discharge 10 minutes after low water slacks 

Typical year discharge event at spring low water slack