The Sun.
London, England, 1853-10-21 00:00:00

that fully ten times this amount will ba required to put
the drainage of London into a proper condition.

SOUTH SIDE OF THE THAMES.
SURREY AND KENT DRAINAGE.

REPORT OF MR. BAZALGETTE.
" Pursuant to your instructions of the 20th ult., I have,
.in consultation with Sir William Cubitt, prepared a de-
sign for a high level or catchwater sewer ; which, in con-
junction with the low level sewer (the plans for which have
already been laid before you), will complete the main fea-
tures of a design for the effectual drainage of the metropo-
litan districts on the south side of the Thames, and the di-
version of the sewage to a lower point in that river ; whence
it will admit of still further removal from the metropolis,
as soon as the commissioners shall be enabled to carry out
the necessary works.
" In preparing this design, it has been sought, as far as
practicable, to comply with the resolutions of the commis-
sioners in 1850, communicated to their engineer, the late
Mr. Forster, on the subject of the main drainage; and in
describing the proposed scheme, it will be necessary, first,
to call your attention to the natural features of the district
to be drained, which is represented by the portions re-
spectively coloured green, pink, and blue upon the accom-
panying map, and which covers an area of about 24 square
miles. _ _

" The urban districts and more closely populated suburbs
are bounded on the north by the riwer Thames, on the east
by the river Ravensbourne, and en the west by the river
Wandle; the southern boundary being a summit, or water-
shed level, about Mitcham, Streatham, Norwood, and
Sydenham. The river Thames now receives the drainarge
of this district from the:Heathwall, the Effra, the Battle_
bridge, the Great St. John's, the Duffield, the Ea :74 and
several minor sewers, along its course, for a ler,gth of 11
miles, between, the outlets of the rivers Wardle and Ra-
vensbounae. It is not proposed to intercept the rainfall
upon the lands adjoining these two lareA.nientined rivers;
they will continue to receive it as heretofore. But it is
proposed to divert from those lanr!s, as far as practicable,
the drainage of such roads and:eniklings as may be built
upon them.

" The northern half of
districts coloured, pink a- the entire area, comprising the
ur-
ban, and its general P:
are blue upon the map,
is
high-water to 6 fes", varies.from the level of Trinity
mostly
doubtless, at
one period, bes below it. This tract has,
names,
alt 'n a marsh covered by the waters
of the
basement-, cough many of the houses upon it have now
Tsae -soantd cellars below the ground.
se!...eirb u hern half, coloured green upon the map, is
an, and its surface falls rapidly towards its northern
or lower margin ,
from an elevation of 350 feet higher ; so
that, during heavy rains,
from the floods the whole of the
upper district descend
with great rapidity into the sewers
of the two lower districts •
and the mouths of those sewers
being closed by the waters; in the Thames for about eight
hours each tide, the sewers themselves moreoverin-
sufficient to store the storm waters
the
being
during that period the lower districts ,are
flooded.result is, that
"It will be evident that it is impossible
maintain to a
continual and unintermitting flow in the sewers of the two
lower districts, or to drain the cellars and subsoil, and
make them dry and healthy, without the aid of pumpins.
" The first object, therefore, has been, so to intercept
the waters from the suburban, or high district, as to carry
off the largest possible amount by gravitation ; and having
thus relieved the low districts from periodical inundations
whereby their size is reduced to a manageable limit, to
deal with them as hereinafter described.
" The high level intercepting sewer commences at the
north-west corner of Clapham-commas, being of the ordi-
nary form. (3' x2' 6"), and falling at the rate of lix
341 to its, junction with its northern branch, at the point
marked B on the accompanying map ; its route to this
point beins. through Clapham Park-road, Acre-lane, and
Cold Harbour-lane, where it intercepts the Effra Sewer
near the Brixton-road, its size increasing in proportion to
the amount of drainage to be received by it, up to 9 feet
6 inches in diameter at the point B, where it receives the
drainage from 2,200 acres. From this point the main line
falls as the rate of 1 in 1,760, or 3 feet per mile, to its out-
let. And from the junction with the northern branch
to the junction with the southern branch, viz.,—
between B and D, it is twelve feet in diameter, and
drains 3,500 acres, its direction being through Cold
Harbour-lane, Love-walk, and fields to the point D,
in the Lyndhurst-road, where it receives the southern
branch. From this point to the outlet, it is increased
to two parallel culverts, each 11 feet in diameter,
passing mainly through fields and garden ground, and under
the Brighton and North Kent Railways, near New-cross
stations, to the mouth of the Ravensbourne, at Deptford-
creek, into which it will discharge the drainage from 7,850
acres by gravitation, at high water of the highest tides.
" The northern branch commences with a sewer 4 feet in
diameter, by a junction with an existing sewer in Rectory.
grove, Clapham ; and it falls at an inclination of 1 in 175,
through Larkhall-lane to Union-road. Here it increases to
6 feet in diameter, and falls to its junction with the main
line at the point B, in Cold Harbour-lane, at the rate of 1
in 1,472, again intercepting the Effra sewer at a lower
point in the Brixton-road, and draining 650 acres through
a seven feet sewer.
" The southern branch, or Effra diversion, commences
by a junction with the Efrra sower at Croxted-lane, near
Dulwich. It falls, at an inclination of from Ito 273 to 1
in 100, in a direct line, to its junction with the main sewer
at the po int D, in the Lyndhurst-road ' being 9 feet in
diameter, and receiving the drainage from 3,100 acres.
" These branches are important parts of the high level
sewer, and without them it will not answer. In particular
the southern branch will save the covering of an equal
length (about 2 miles) of the present open Effra sewer, the
waters of which, instead of descending by a circuitous
route, and with a flat gradient, into the lower districts,
will be diverted at a high level to a point nearer the out-
-fall ; and thus the size and cost of the upper portion of the
main line will be reduced to one-half of what would other-
wise be required, whilst a deep outfall for a new district
now subjected to floods, namely, Dulwich, will be pro-
" Taking the more comprehensive view of the drainage of
the whole area, it is proposed to extend and slightly alter the
design for the low level sewer laid before the committee, on
the 20th ult., so as to include the drainage of Battersea and
Battersea-fields. The present scheme commences with a
circular sewer, 5 feet in diameter, at the level of the bed of
the Falcon-brook, Battersea. It passes along Battersea-
road, under the South-Western Railway, along Priory-
road, Lansdowne-road, and the Clapham-road, to St.
Mark's Church, Kennington-common ; up to which point
its inclination will be one in 1,760, or three feet per mile,
and its size will then have been increased to 8 feet in dia-
meter. From this point it proceeds in the direction of
Mr. Forster's line, by the side of the Surrey Canal to Old
Kent-road, at an inclination of 1 in 2,212, or 2 feet 6 in.
per mile ; being at this point 9 feet in diameter. It
then proceeds along the Old Kent-road, in Cold Blow-
lane, where it leaves Mr. Forster's lino ; taking a direct
course across the fields and market gardens, under the
Brighton and North Kent-railways, along New Douglas-
street, and Griffin-street, to High-street, Deptford ; its in-
clination for this length being 2 feet per mile, or 1 in
2,640 ; and its size 13 feet in diameter. Up to this point
it receives the drainage from 4,450 acres, coloured pink
upon the map. At High-street, Deptford, its size is in-
creased to 12 feet in diameter, being intended, eventually,
to receive here an important branch sewer from the lower
Deptford-road, which will divert from the Thames the
drainage of about 3,300 acres, coloured blue upon the map.
The main line then passes between the Gas and Vitriol
Works, near the Greenwich Railway, and under Deptford
Creek to a vacant piece of ground, well adapted for a
pumping-station, or for sewage manure works, or for con-
tinuing the lino at some future time further eastward.
" The lift from the bottom of the sewer to Trinity high-
water ma, k, would here be 30 feet ; and from 1,500 to
2,000 horse-power would have to be provided at the pump-
ping station.
" The lengths of the proposed sewers would be as fol-
low :—High Level Sewer, main line, 6 miles 2 furlongs;
north branch, 2 miles ; south branch, 2 miles 1 furlong :
total, 10 miles 3 furlongs. Low Level, main lice, 7 miles
4 furlongs; north branch, 2 miles 3 furlongs; total, 9 mil es
7 furlongs. Grand total, 20 miles 2 furlongs.
" The sections of these sewers are of a favourable cha-
racter : their inverts generally average from 20 to 30 feet
below the surface ; and a very small portion of the work
will have to be tunelled.
" Careful attention has been paid to the character of
the surface under which the sewers aro to be constructed ;
private property and houses have been avoided as much as
possible; but, owing to the streets being irregularly laid
out, it has not been practicable to effect this altogether,
and in such cases the comparative value of the property
has been duly considered.
" It will be observed that, to save the permanent cost of
pumping, the gradients of the low level sewer have been re-
duced ; but the increase in the size of a sewer compensates
for a loss of fall and the sewers will still maintain,
through their whole length, a velocity of current varying
from 1 to 2 miles per hour, with the ordinary flow of
sewage, and during rains that velocity will bo increased.
In this sewer there will be a constant current of a largo
body of water, so that the average velocity will be suffi-
cient to keep it clear from ordinary deposit ; but there
will also be a good opportunity of flushing it, together
with the other sewers in this district, from the catchwater
sewer and the Thames at high water.
" The minimum velocity of current in the high level
sewer will be about 2i miles per hour •
; whilst at the upper
end it will be considerably more.
" The sizes of the sewers now proposed are larger than
any heretofore recommended to the commissioners ; and I
would here beg leave to refer to that part of the report of
Mr. Haywood and myself, on the Great London Drainage
Scheme, contained iu page 23, wherein we argue—
" ' That the drainage of those portions of the metropolis
at present requiring a deeper outfall, must not bo made
dependent upon any scheme of interception, unless such•
scheme is adequate to carry off the rainfall as well as the
sewage from them. It, therefore, follows, that whatever
scheme of interception is eventually adopted, if it be short
of such capacity, the sewerage and drainage of the metro-
polis must be perfected and completed independently of it.'
" If this seasoning be sound, it is manifestly more eco-
nomical to construct one work which will answer every
purpose, than to complicate it by the execution of dupli-
cate sewers, in order to gain the same object which Islay
obtained by one ; and it remains only to show s well
these sewers are sufficient to carry off the rainfall, v
as the sewage, from the districts for which they will be
the outfall,
amounting to 30
"An average of an annual rainfall amoun would
inches, added to the maximum daily flow ofn sewag
e,
u dis-
give only 3,000 cubic feet per minute upo p t per
whilst
trier, and 4,000 cubic feet upon the lower th
etdel
one or two
extraordinary thunderstorms, amounts
h7,wover, generally
inches in an hour, are recorded ; these,
ound absorbs and
occur during the hot seasons, when 9.2,e_girin. Such storms
the air evaporates a large potion Jaw.
small district at one
are generally partial, covering u
btion so that the whole of
time, and are never of long dare;
the
'district do not reach
the waters that have fe.lionrupeel
storm has abated ; and
the outfall sewer until after
being pre-occupied at the
small portion only of the tester
the remaining portion for
commencement of the s ters A heavy anl
floe( wa • orm
some time stores the
,zobably the most severe ordeal to
rain of long durationl
subjected, when the roundg and the
which sewers are
to their full extent,
e charged absorption and
air
having becom
• tion abstract , but little from the sewers, and the
feeder sewers
evapoiahaving also become charged, would be deli-
veriug to their full extent.
" The largest quantity of rain which fell
during the wet season of 18.:2
day in London in one
measured 1 inches, but
storms amounting to 2i inches in a
occurrence, have been recorded , and day, alth-ough of rare
into the high level sewer 45,000 cubic these would deliver
it is capable of discharging feet per minute, wLilst
level sewer will discharge 21 ?wards of 46,000. The low
it is here proposed that the 00. cubic feet per minute, and
districts shoal.'act existing main sewers in the low
as resery •
storms. From their ens during such extraordinary
construction and the remarkable flat-
ness of their level, they •
are peculiarly adapted to this ob-
ject ; and it
would store is estimated that, on these occasions, they
the surplus floods without the rising of the lat-
ter to an inconvenient height, and would again deliver their
contents into the Thames at low water, or into the inter-
cepting sewer 34 it became free to receive them. Thus the