The London sewerage system is
part of the water infrastructure
serving London. The modern system
was developed during the late
19th century, but as London has
grown the system has been expanded
and needs further investment.
History
During the early 19th century the
River Thames was practically an open
sewer, with disastrous consequences
for public health in London, including
numerous cholera epidemics. Proposals
to modernise the sewerage system had
been made during 1856, but were neglected
due to lack of funds. However, after
The Great Stink of 1858, Parliament
realised the urgency of the problem
and resolved to create a modern sewerage
system.
Joseph Bazalgette, a
civil engineer and Chief Engineer
of the Metropolitan Board of Works,
was given responsibility for the work.
He designed an extensive underground
sewerage system that diverted waste
to the Thames Estuary, downstream
of the main centre of population.
Six main interceptory sewers, totalling
almost 100 miles (160 km) in length,
were constructed, some incorporating
stretches of London's 'lost' rivers.
Three of these sewers were north of
the river, the southernmost, low-level
one being incorporated in the Thames
Embankment. The Embankment also allowed
new roads to reduce traffic congestion,
new public gardens, and the Circle
Line of the London Underground.
The intercepting sewers,
constructed between 1859 and 1865,
were fed by 450 miles (720 km) of
main sewers that, in turn, conveyed
the contents of some 13,000 miles
(21,000 km) of smaller local sewers.
Construction of the interceptor system
required 318 million bricks, 2.7 million
cubic metres of excavated earth and
670,000 cubic metres of concrete.
Gravity allows the sewage
to flow eastwards, but in places such
as Chelsea, Deptford and Abbey Mills,
pumping stations were built to raise
the water and provide sufficient flow.
Sewers north of the Thames feed into
the Northern Outfall Sewer, which
feeds into a major treatment works
at Beckton. South of the river, the
Southern Outfall Sewer extends to
a similar facility at Crossness.
During the 20th century,
major improvements were made to the
sewerage system and to the sewage
treatment provision to reduce substantially
pollution of the Thames Estuary and
the North Sea.
Modern development
needs
Victorian pipes now comprise less
than 1% of the total sewerage network
in London.
The original system
was designed to cope with as much
as 6.5 mm (1/4”) of rainfall
within the catchment area, and supported
a smaller population than today’s.
London's growth has therefore put
pressure on the capacity of the sewerage
system. During storms, for example,
high levels of rainfall (in excess
of 6 mm) in a short period of time
can overwhelm the system. Sewers and
treatment works are unable to cope
with the large volumes of rainwater
entering the system. Rainwater mixes
with sewage in combined sewers and
excess mixed water is discharged into
the Thames. If this does not happen
quickly enough, localised flooding
occurs (surcharge). Such sanitary
sewer overflow can mean streets becoming
flooded with a mixture of water and
sewage, causing a health risk.
Increasing the carrying
capacity of London’s sewerage
system has been debated for some years.
Proposals for the 'Thames Tideway'
include a wide diameter storage-and-transfer
tunnel (internal diameters of 7.2
m and 9 m have been suggested), 22
miles (35 km) long, underneath the
riverbed of the Thames between Hammersmith
in the west and Beckton/Crossness
in the east, but as the cost of such
a megaproject is likely to be substantial
(estimated at £1.7 billion in
2004), investment decisions have been
slow to be forthcoming. In March 2007
the Mayor of London announced that
the project will proceed with completion
expected by 2020.
Because design and construction
of such a tunnel will take an estimated
15 years, a shorter-term (and slightly
lower cost) interim solution has also
been developed. This £1.6 billion
scheme (2006 prices) involves two
shorter tunnels (one taking storm
water from Hammersmith to Battersea
for treatment or storage, the other
carrying water from Abbey Mills south
to the river at Beckton) and improvements
to associated treatment facilities.
These four steam massive steam engines
were used to pump sewage out of Leicester
up to the treatment works at Beaumont
Leys. They were completed in 1891
and ran until 1964 when they were
preserved. They can be seen running
at special events throughout the year.
