Tideway

The Tideway is a name given to the part of the River Thames in England that is subject to tides. This stretch of water is downstream from Teddington Lock and is in its widest definition just under 160 kilometres (99 mi) long. The Tideway includes the Thames Estuary, the Thames Gateway and the Pool of London.

Tidal activity

Depending on the time of year, the river tide rises and falls twice a day by up to 7 m (24 ft) and due to the need to overcome the outflow of fresh water from a significant part of England takes longer to subside (ebb) (6–9 hours) than it does to flow in (4–5 hours).

London Bridge is used as the basis for published tide tables giving the times of high tide. High tide reaches Putney about 30 minutes later, similarly Teddington/Ham.

Low-lying banks of London have been defended against natural vulnerability to flooding by storm surges. The threat has increased due to a slow but continuous rise in high water level, caused by the extremely slow 'tilting' of Britain (up in the north and down in the south) due to post-glacial rebound and the gradual rise in sea levels due to climate change. The Thames Barrier was constructed across the Thames at Woolwich to deal with this threat.

Thames Tideway Scheme

The Thames Tideway scheme or Thames Tideway Tunnel is an under-construction 25 km (16 mi) tunnel running mostly under the tidal section of the River Thames through central London, which will provide capture, storage and conveyance of almost all the combined raw sewage and rainwater discharges that currently overflow into the river. The tunnel will be owned by Thames Tideway Tunnel Ltd (a new regulated Infrastructure Provider), constructed by Bazalgette Tunnel Ltd (a consortium of companies including Thames Water) and operated by Thames Water. On 3 November 2015, Bazalgette Tunnel Ltd received its operating licence from OFWAT, ensuring the start of the project.

Starting in 2016, construction of the Thames Tideway Tunnel will take seven to eight years, giving a target completion date of 2023. Once constructed, the main tunnel will have an internal diameter of 7.2 m (24 ft) and will run from −30 m (−98 ft) at Acton in the west of London for over 25 km (16 mi) under central London down to −70 m (−230 ft) at Abbey Mills in the east. It will connect 34 of the most polluting combined sewer overflows (CSOs), via transfer tunnels, and is expected to reduce the number of overflow events to a maximum of four per CSO per year at time of commissioning, increasing gradually due to effects of climate change and population growth. The tunnel will transfer the captured sewage to the Lee Tunnel for onward delivery to Beckton Sewage Treatment Works for treatment. The recycled clean water is then released into the River Thames.