While he was recovering, London's Metropolitan Commission of Sewers ordered that all cesspits should be closed and that house drains should connect to sewers and empty into the Thames. As a result, a cholera epidemic (1848–49) killed 14,137 Londoners.
Bazalgette was appointed assistant surveyor to the Commission in 1849, taking over as Engineer in 1852. Soon after, another cholera epidemic struck, in 1853, killing 10,738. Medical opinion at the time held that cholera was caused by foul air: a so-called miasma. Physician Dr John Snow had earlier advanced a different explanation, which is now known to be correct: cholera was spread by contaminated water. His view was not then generally accepted.
Championed by fellow engineer Isambard Kingdom Brunel, Bazalgette was appointed chief engineer of the Commission's successor, the Metropolitan Board of Works, in 1856. In 1858, the year of the Great Stink, Parliament passed an enabling act, in spite of the colossal expense of the project, and Bazalgette's proposals to revolutionise London's sewerage system began to be implemented. The expectation was that enclosed sewers would eliminate the stink ('miasma'), and that this would then reduce the incidence of cholera.
Bazalgette's solution was to construct a network of 82 miles of enclosed underground brick main sewers to intercept sewage outflows, and 1,100 miles (1,800 km) of street sewers, to intercept the raw sewage which up until then flowed freely through the streets and thoroughfares of London. The plan included major pumping stations at Deptford (1864) and at Crossness (1865) on the Erith marshes, both on the south side of the Thames, and at Abbey Mills (in the River Lea valley, 1868) and on the Chelsea Embankment (close to Grosvenor Bridge; 1875), north of the river. The outflows were diverted downstream where they were collected in two large sewage outfall systems on the north and south sides of the Thames called the Northern and Southern Outfall sewers. The sewage from the Northern Outfall sewer and that from the Southern Outfall were originally collected in balancing tanks in Beckton and Crossness respectively before being dumped, untreated, into the Thames at high tide.
The system was opened by Edward, Prince of Wales in 1865, although the whole project was not actually completed for another ten years.
The unintended consequence of the new sewer system was to eliminate cholera everywhere in the water system, whether or not it stank. The basic premise of this expensive project, that miasma spread cholera infection, was wrong. However, instead of causing the project to fail, the new sewers succeeded in virtually eliminating the disease by removing the contamination. Bazalgette's sewers also decreased the incidence of typhus and typhoid epidemics.
Bazalgette's work had a longer term impact in that he designed the diameter of the sewage pipes to be far in excess of what was needed at the time, stating, “…we're only going to do this once and there's always the unforeseen”. His foresight allowed for the unforeseen rapid increase in London’s populations and the sewers are still in use today,
Bazalgette died on March 15th 1891, and was buried in the nearby churchyard at St Mary's Church.
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