Engineering Wonders of the World
Volume III

THE DRAINAGE SYSTEM OF LONDON. 211 The old Sewers and Cesspools. miles of the earth’s surface has contributed in no small degree to the difficulties, since the rainfall on this great area must be dealt with by entirely artificial drainage. The rain that falls in a country district is mostly absorbed by the ground. Only when the fall is very heavy do the ditches fill and overflow. In a town a thunderstorm would soon convert the streets into lakes were not suitable arrangements made for carrying off the water as fast as it falls. The old sewers of London were constructed to deal with the rainfall only, and mostly- followed the lines of old water courses. Early in the nineteenth century cesspools were introduced to receive the sewage from houses. Until 1815 the law forbade the discharge of house sewage into sewers ; but as the cesspools proved to be quite insufficient for their purpose, legislation first permitted and then (1847) compelled house drainage to be discharged into the sewers. Within a period of about six years no fewer than 30,000 cesspools were abolished in the London area, and all house and street refuse was turned direct into the Thames. Now, a large part of London lies so low that sewers running through it into the river must discharge below high-water level. This fact had most unpleasant conse- Difficulty in quences Sewage could escape discharging , , . , . „ • / only at or near low water. As Sewage into J the Thames. rose sewage from the high ground as well as the low was ponded back in the sewers. The heavier ingredients settled and accumulated. During rainy periods, and especially at high tide, the sewers overflowed into the houses. Even if the sewage did find its way into the Thames it was merely washed backwards and forwards by the tides, and served to form foul accumulations on the river banks. At last the situation became so intolerable that public opinion demanded a remedy. In Reforms urgently needed. The Present System of intercepting Sewers. 1856 the recently formed Metropolitan Board of Works requested their chief engineer, the late Sir Joseph Bazalgette, to draw up plans for a system of discharging all the sewage of the Metropolis into the river at a point below London where it would prove less obnoxious. The fact that the land rises gradually from the Thames both northwards and southwards greatly assisted the evolution of a scheme of intercepting sewers running roughly west and east. The scheme authorized in 1856 and executed between that year and 1874, may be sum- marized briefly thus. On the north side were made three inter- cepting sewers—a high-level sewer, 7| miles long, running from Hampstead to Old Ford, at which point it met a middle- level sewer, 9J miles long, from Willesden, both of which sewers flow by gravitation. From Old Ford these two sewers discharged into the Thames at Bark- ing through an outfall sewer, 51 miles long, and consisting of two culverts 9 feet by 9 feet, from Old Ford to Abbey Mills, and three lines from the latter point to Barking, raised above ground in embankment. Closely following the north bank of the river for a considerable part of its course, a low-level sewer ran 13| miles from Hammersmith to Abbey Mills, a point on the main outfall sewer. As the area drained by this sewer is very low-lying, the necessary gradient to Abbey Mills would have been too deep for one lift, and to obviate this difficulty there was constructed an intermediate pumping station at Pimlico, raising the sewage west of this point about 19 feet into another sewer, which falls to 18 feet below Ordnance datum at Abbey Mills. Here the sewage is further raised a height of between 36 and 40 feet into the main outfall sewer referred to above.