A. The Thames should be kept free from sewage whatever the state of the
tide.
B. There should be intercepting drains to carry off the sewage (so
keeping the Thames unsoiled by it) wherever practicable.
C. The sewage should be raised by artificial means into a main channel
for removal.
D. The intercepting sewers should be so constructed as to secure the
largest amount of effective drainage without artificial appliances.
In preparing his plan, Mr. Forster had the advice and assistance of Mr.
Haywood, of the City Court of Sewers.
The metropolis is divided into two portions--“the northern portion of
the metropolis,” or rather that portion of the metropolis which is on
the north or Middlesex bank of the Thames; and the southern portion, or
that which is on the south or Surrey side of the river.
The northern portion is in the new plan considered to “divide itself
into two separate areas,” and to these two areas different modes of
sewerage are to be applied:
“1. The interception of the drainage of that district, which, from
its elevation above the level of the outlet, is capable of having its
sewage and rainfall carried off by gravitation.
“2. The interception of the drainage of that district, which, from its
low lying position, will require its sewage, and in most localities its
rainfall, to be lifted by steam-power to a proper level for discharge.”
The first district runs from Holsden-green (beyond the better-known
Kensall-green) in the west, to the Tower Hamlets in the east. Its
form is irregular, but not very much so, merely narrowing from
Westbourn-green to its western extremity, the country then becoming
rural or woodland. Its highest reaches to the north are to Highgate and
Stamford-hill. The nearest approach to the south is to a portion of
the Strand, between Charing-cross and Drury-lane. Care has evidently
been taken to skirt this district, so to speak, by the canals and the
railroads. This division of the northern portion is described as “the
district for natural drainage.”
The area of this division is about 25-1/6 square miles.
The second division meets the first at the highway separating
Kensington-gardens from Bayswater; and runs on, bordering the river,
all the way to the West India Dock. Its shape is irregular, but,
abating the roundness, presents somewhat of that sort of figure seen
in the instrument known as a dumb-bell, the narrowest or hand-part
being that between Charing-cross and Drury-lane, skirting the river
as its southern bound. At its eastern end this second district widens
abruptly, taking in Victoria-park, Stratford, and Bromley.
The area of this division of the northern portion is 16-1/8 square
miles.
There are, moreover, two small tracts, comprising the southern part of
the Isle of Dogs, and a narrow slip on the west side of the river Lea,
which are intended to allow the rainfall to run into the Thames and the
Lea respectively.
The area of the two is 1-3/4 square mile.
The area to be drained by natural outfall comprises, then, 25-1/6
square miles as regards rainfall, and the same extent as regards
sewage; while the area to the drainage of which steam power is to
be applied comprises 14-1/3 square miles of rainfall, and 16-1/6
square miles of sewage; the two united areas of rainfall and sewage
respectively being 39-1/2 and 41-1/3 square miles.
The length of the great “high-level sewerage” will be, as regards the
main sewer, 19 miles and 106 yards; that of the “low-level sewerage,”
14 miles and 1501 yards.