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towards it. These conduits fall in an easterly direction, and are continued down to points on the banks of the river below London, where the sewage, intercepted and carried off by them, is discharged.

In such of these intercepting conduits as are at sufficient altitude, the sewage flows away by gravitation. But as many parts of the metropolis lie so low as to render this impossible, the contents of the intercepting conduits there have to be pumped up by steam power, in order to raise them to the necessary level of discharge. The entire system is naturally separated into two great divisions, lying on the north and south of the river respectively.

(151) Northern Interception. (See map.)

On the north side there are three great lines of interception:1. A line called the Northern High Level Sewer, which, beginning in the north-west at Hampstead and Highgate, passing by Hackney, descending by Stratford, and crossing over the river Lea near Bow, abuts upon the Thames at Barking Creek. This conduit acts entirely by gravitation.

2. A line at a lower level called the Northern Middle Level Sewer, which begins in the west at Kensal Green, passes through Oxford Street, Clerkenwell, and Bethnal Green, and joins the Northern High Level Sewer near Bow. This conduit also works entirely by gravitation.

3. A line at a still lower level called the Northern Low Level Sewer. It begins in the extreme west at Chiswick, and passes through Chelsea, near the bank of the river, as far as the Grosvenor Road, Pimlico. Here, near the Victoria Railway Bridge, its contents are pumped into another conduit lying slightly higher, which runs along the northern Thames embankment, and near the river to the Tower, then striking off to the north-east through Stepney to Abbey Mills, near Stratford, where the contents are again pumped up to the level of the Northern High and Middle Level Sewers.

From this point the whole of the northern drainage flows through the Northern Outfall Sewer to the Thames; this outfall sewer is formed of three parallel conduits, which take the contents of the three sewers, but can be made to communicate when necessary to equalize the flow.

(152) Southern Interception. (See map.)

On the south side of the river there are two great lines of interception

1. A line called the Southern High Level Sewer, which begins at Balham and passes through Clapham, Brixton, Camberwell, and New Cross, crosses under Deptford Creek by iron syphon pipes, and continues through Greenwich, Woolwich, and Plumstead Marshes to a pumping station on the right bank of the river at Crossness. The sewage reaches that point by gravitation.

2. A line called the Southern Low Level Sewer. It begins in the extreme south-west at Putney, and passes through Wandsworth, Battersea, Vauxhall, Kennington, Peckham, and New Cross, to a pumping station on the Ravensbourne, near Deptford, where the contents are pumped into the Southern Outfall Sewer.

At a certain point near Nine Elms there is a pumping station, which lifts into this sewer the drainage brought down by the sewers on the river Effra.

There is also a branch conduit from the districts of Bermondsey and Rotherhithe, which delivers to the Deptford pumping station, the contents being then pumped into the Southern Outfall Sewer. From Deptford the united sewage flows down to Crossness by the Southern Outfall Sewer.

At Crossness the whole is pumped by steam power to the height necessary to allow it to flow into the river.

The following data, given in evidence before the Royal Commission by Sir Joseph Bazalgette, will give a general idea of the magnitude of the works :

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Area of Metropolis [North] not drained into intercepting sewers.

1.47B

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A. Of this area 3.40 square miles is common or park land, and 0.87 square miles is water.

B. This area consists of parts of Hackney marshes, North Woolwich, and a detached part of the metropolis near Muswell Hill.
c. In addition to the above, the district of the Hornsey Local Board contributes sewage from a present population of about
22,000, the quantity being restricted ultimately to 500 cubic feet per minute. A part of the Stamford Brook drainage area
contributes also the sewage from a small population, but its number cannot be ascertained. The same area also contributes
surface water to the metropolitan system, but the Metropolitan Board have determined to intercept this from their sewers and
discharge it into the river at the extreme western boundary of the Metropolis. This is one of the works included in the
1,500,000l. to be expended to prevent floodings from rain.

49.97

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