The Landscape Guide

Landscape, environmental and visual impact of the Thames Tideway Tunnel

See index page for Chelsea to Tower Thames Landscape Strategy

For about 300 days/year the water quality in the London Thames is remarkably high. But on the remaining days, when there has been heavy rain, it is polluted and the London is in breach of European Law. This is because much of London is drained by combined sewers. They carry both rainwater and sewage water. In normal conditions they can cope but in flood conditions they discharge into the Thames and its tributaries. Thames Water, the company responsible for London sewage, has a preferred solution: a tunnel sunk in the bed of the tidal section of the Thames. This tunnel would catch all the outflows and prevent sewage pollution of the river.

  • The environmental benefits would be (1) cleaner water on approximately 65 days/year (2) slightly improved habitat conditions in the river (3) removal of a slight risk to public health.
  • The environmental dis-benefits would be (1) the construction of wharfs for underwater pumping stations - they would be a visual intrusion on the riverscape and would narrow the tideway channel (2) a decade of visual and environmental disruption during the construction period.

An alternative to the Thames Tideway Tunnel, proposed by, makes use of Sustainable Urban Drainage Systems (SUDS) techniques. The capital costs of this alternative are estimated to be much lower while the landscape and environmental benefits are (1) much higher (2) evenly distributed throughout Greater London.
The SUDS alternative functions by detaining and infiltrating rainwater close to where it falls. This prevents the combined sewers from becoming overloaded. Their normal operation, as on the other 300 days/year, continues and no sewage is discharged into rivers.