Ratcliff beach in London's East End is where the ESO (Emergency Sewer Overflow) for North London discharges into the Thames river. The brick sewer outfall is 100" or 2.6m in diameter and dates from 1861. It was built during the modernisation of London’s sewer system devised and overseen by Joseph Bazalgette.
As is typical of Victorian sewers constructed during this period, the sewer is egg-shaped and thus not easy to find a check valve solution for it. However, given the wide tidal range of the Thames, it is important to prevent backflow putting strain on the drainage system upstream, while at the same time ensuring that any large flows generated during storms can be released into the Thames.
The existing flap valves have had many modifications made to them over the years, but the sewer was always half full of water. Closer inspection of the sewer revealed evidence of even older flap valve constructions that had obviously failed and/or been removed at some stage over the sewer’s life.
The GuvNu solution proposed by MeasurIT is a custom fabricated assembly in 316 stainless steel that is easily assembled on site and requires no confined space entry. The four 24"/600mm flanged Tideflex Ultraflex Checkmate valves allow an aesthetically acceptable short length without protruding into the river. CheckMate valves have a low headloss and are also not very vulnerable to blockage by debris.
The municipal owner has fitted a camera behind the valves and the sewer upstream is now drained down. Shortly after fitting, there was a substantial quantity of silt carried through the valves as the pipe was no longer filled at each tide.
The increased storm storage that is now possible alleviates flood risk and the reliable backflow prevention provided by the GuvNu valve array prevents salt water intrusion to the network, reducing treatment cost significantly.
This short video gives an overview of the valve functioning with a little bit of steam punk flair to suit its location history.