The Sun.
London, England, 1856-04-04 00:00:00

THE SUN, LONDON, FRIDAY EVENING, APRIL 4, 1e56,

METROPOLITAN BOARD OF WORKS.
(This Day.)

that with a bottom velocity of 16 inches per second only
(or 0.9 miles per hour), heavy pieces of briek, stone, &e.,
will be removed, and that with a velocity of 21i inches
(or 1.24 miles per hour), even iron borings and heavy slag
will be removed. The above minimum velocity will there-
fore be sufficient.' Mr. Beardmore, in his work on Hy-
draulics, states (p. 8) that A velocity of 150 feet per
minute (or 1 miles per hour), will generally prevent de-
posit in pipes and sewers.' Mr. John Phillips states (see
first report of Slnitary Commission, 1847, p. 177),
From observation and experiment, I find that it requires
a constant velocity of current to be running through the
sewers, equal to about 2 feet per second, or 1 miles per
hour, to prevent the soil from depositing within them.'
"Professor Robinson, in his ' Theory of Rivers,' states,
at page 465, that " we learn from observation that a ve-
locity of three inches per second at the bottom will just
begin to work upon fine clay for pottery, and, however
firm and compact it may be, it will turn it up. . . .
A velocity of six inches will lift fine sand ; eight inches
will lift sand as coarse as linseed; 12 inches will sweep
along fine gravel ; 24 inches will roll along rounded pebbles
an inch in diameter, and it requires three feet per second
at the bottom to sweep along shivery angular stones of the
size of an egg.'

The weekly meeting of this board was held this after-
noon at the Council Chambers, Guildhall; Mr. Thwaites,
in the chair.
DRAINAGE OF THE DISTRICTS SOUTH OF THE THAMES.

The principal subject brought before the board was
the report of the engineer, Mr. Bazelgette, relating to
the drainage of the districts south of the Thames, which
was read and afterwards ordered to be printed for the
information of the Loard, and its consideration was ac-
cordingly adjourned.

The following is the elaborate report of the engineer
en ttis important subject :
" Greek-street, Soho, 3d April, 1856.
" Mr. Chairman and Gentlemen—ln carrying out the
foregoing instructions, my attention has been directed first
to that portion of the metropolis which lies upon the south
side of the river, where improved drainage is most ur-
gently required. The Board will probably remember that
in 1.53, pursuant to directions by the then Metropolitan
Commissioners of Sewers, designs for intercepting sewers
on the south side of the river were prepared by me. The
plan now submitted for your coasileration will be found to
resemble, in its main features, the former scheme ; it
therefore becomes necessary to recapitulate several of the
leading considerations referred to in my report of 1853, and
in the joint report by Mr. Haywood and myself upon the
northern drainage in 1854, whilst I have at the same time
endeavoured to take advantage of all the information
gained in the subsequent preparation of the northern
drainage scheme, and to profit by the experience of the
last three years. The modifications now introduced will,
I trust, be regarded by you as improvements.
" In 1849 the Commissioners of Sewers publicly invited
plans and suggestions for the main drainage of the metro-
polis, and their invitation was warmly responded to by
many who were interested in the subject. 116 plans were
sent in; all of which I, in conjunction with Mr. Cresy,
examined and classified, and they were reported on by a
committee of the Commissioners of Sewers, consisting of
Sir J. F. Burgoyne, Captain Vetch, Jas. M. Bendel, Esq.,
Captain H. D. Harness, and Robert Stephenson, Fsq.,
whose report was printed and laid before Parliament.
•ther plan sand suggestions subsequently received'
were considered and printed by the Commissioners of
Sewers.

" Mr. Stephenson and Mr. Hawkesley consider a velocity
of two miles per hour ample where there is a continual
stream, and these opinions are further• confirmed by the
experience of Mr. Haywood and myself.
With reference to the fall requisite to produce this
velocity, the calculations universally adopted by hydrau-
lic experimenters and engineers, and upon which my esti-
mates are based, show that in a sewer 9ft. Gin. in dia-
meter with a fall of 2 feet per mile, the mean velocity
would bo about 2 miles per, hour when running three
quarters full, or 1.88 miles per hour when running half
full, and about 1 2-3 d miles per hour when running one-
third fall.

" But the velocity of a stream is governed by the di-
mensions of its channel, as well as by its rate of fall. Thus,
in a sewer 10 feet in diameter with a fall of 2 feet per
mile, there will be the same mean velocity of stream when
running half full, as in a sewer 2 feet in diameter with a
fall of 10 feet per mile.
" Where ecoeomy of fall is required, it is desireable, so
far as other considerations will permit, to graduate the
declivity of the sewers so as to produce an uniform rate
of flow in them, and thus to avoid a waste of fall in one
portion of the design, and an insufficient velocity in an-
other.

" When the proper velocity and the practicable limits
which can be assigned to the fall are ascertained, it is easy
to determine the size of the sewer requisite to carry off a
constant and defined quantity of sewage in a given time.
"On the other hand, when in dealing with drainage
()Wiens, we have to provide for rains variable in amount
and duration, and where absorption, evaporation,
and the time occupied by the waters in flowing
from the points on which they fall, over various
surfaces and levels to the point of discharge have
to be taken into account, the question is more com-
plicated, and it is under such conditions that we are in-
dobted to Mr. Hawkesley's formula, with respect to which
➢sir. Stephenson and Sir William Cubitt in their report of
the 11th December, 1854, stated that, 'No part of engi-
neering science has been more industriously investigated
than the laws that govern the flow of water in pipes and
open channels ; and it is probably not too much to say,
that the formula which represent these laws rank amongst
the most truthful that the professional man possesses.
They- have been the subject of laborious experimental in-
vestigation of the most elaborate character, and their re-
sults have been tested by the practical under every variety
of conditions, without their truth being impugned in
the slightest degree. The principles upon which they
are founded have been sanctioned and adopted by Prong,
Eytelivein, Du Beat, and others; and it is to them that
we are indebted, in a great measure, for the simple practi-
cal form which they present. Our own engineers have
modified them to suit particular circumstances, and given
them more extensive usefulness. Mr. Ilawkesley, amongst
others, has especially contributed to render the principles
which they embrace applicable to almost every variety of
condition which the complete drainage of large towns in-
volves, and we shall have occasion, almost immediately,
to adduce some instances within the metropolis, where the
facts confirm theoretical deductions in a very remarkable
manner, and lead irresistibly to the conclusion that they
may be implicitly depended on.'
"The sizes of the sewers required at the various points
of interception are given in the tables and sections ap-
pended to this report. A circular form has been adopted
in this preliminary design, in order to facilitate the pre-
paration of the estimates, and calculations of discharging
power ; but it is proposed to execute them of a slightly
eliptical form, which is preferable in pGint of strength,
and the alteration will have no appreciable effect upon the
estimates or design.
" Having thus briefly touched upon several of the more
leading general principles which govern the design, we
now procesd to the consideration of the works proposed.

" The late Commission expressed their unwillingness to
receive further plans and suggestions, and about 27 were
sent in and are now before this Board. They have been
arranged and classified, and a summary of them is ap-
pended to this report (see Appendix A), whilst it is diffi-
cult to select any one of them as deserving your exclusive at-
tention, many of them boar marks of great thought and
labour, and I acknowledge with pleasure that most of them
contain some useful information or hint.

"Almost every suggestion which can be made upon the
subject has been now so often repeated in some shape or
other, that it would be difficult to determine who were the
first authors of the various schemes and theories pro-
pounded. Having had the advantage of access to all, I
cannot pretend to much originality, my endeavour has
been practically to apply suggestions, originating in a large
measure with others, to the peculiar wants and features of
the different districts, with which my position has made
me famigar.

"Before entering into the details of the plan of drainage
now proposed, it may be well briefly to consider what are
the natural features and requirements of the district to be
dealt with, and what the objects sought to be gained.
" Half of the southern area extends along the south bank
of the Thames, and the surface of the ground is generally
below high water in the river, varying from its level, to
six feet below it.

" This tract is by nature a marsh, which has been re-
claimed from the river by artificial embankments, and is
now closely built over, and thickly inhabited, forming a
large and important portion of the metropolis. Many of
the houses have basements and cellars below the surface,
and the sewers which are beneath them are necessarily so
low that they can only discharge their contents into the
river for about four hours each tile. The sewers being
closed at their outlets for the remaining eight hours, be-
come reservoirs of stagnant sewage for 16 hours in every
day, and unavoidably accumulate deposit. To maintain a
continual and unintermitting flow in the sewers of this
low district and to drain the cellars and subsoil effectually
so as to make them dry and healthy, demands the aid of
pumping. The effect of which has been described by Sir
Wm. Cnbitt and Mr. Stephenson in their report of the
17th Oct., 1853, as being tantamount to raising the level
of the district _0 feet, producing iu its sewers a continu-
ous and free discharge, and entirely overcoming the natu-
ral disadvantages of its situation.
" The remaining portion of the South Metropolitan area
is at preseut thinly covered with buildings, which are,
howevbr, rapidly increasing as the suburbs of the Metisa
polls extend. The surface of the ground rises gradu-
ally from the level of the low district to an extreme ele-
vation of about 350 feet, and the rain waters which fall upon
the high district descend with great rapidity into the
sewers of the low district, which being tide-locked, as
already described, and of insufficient capacity to store a
large and sudden influx of storm waters, during high
water in the river, become overcharged, and in such cases
the sewage floods and destroys muc valualil,3 property.
The suddenness and destructiveness of these inundations
increases in proportion to the progress of building and
drainage in the upper district. To remedy the evil arising
from this cause, it is proposed to intercept the waters of
the upper district, so as to prevent their descending into
the low district, by forming a highlevel or, catehwater sewer,
with a free outlet and a constant discharge by gravita-
tion. The risk and expense attending the process of pump-
ing a large body of water pouring down suddenly at
irregular intervals, where any interruptions in the process
would be productive of great inconvenience and loss, ren-
ders it, in my opinion, expedient to get rid of all the up-
land waters in the manner proposed, by a high level or
catchwater sewer, instead of allowing them to add to the
difficulties, sufficiently formidable in themselves, arising
from the waters falling upon the low district.
"In the plan now proposed, the objects sought to be
attained are twofold and distinct,-Ist, to provide im-
proved outfalls for the drainage of the entire area, and 2d,
by a system of interception to relieve the Thames from the
pollution to which it is now subjecteo. Some of the sewers
proposed are designed to serve the double purpose of drain-
ing and interception, whilst others are simply " Intercept-
ing Sewers," and do not, of themselves, drain the district
through which they pass, but merely supply artificial
channels by which the sewage is diverted from the drain-
age sewers, and carried away to a new and less objection-
able point of discharge into the river.
" With regard to the point of discharge, I cannot do
better than quote from the report of Mr. Stephenson and
Sir William Cubitt, dated the 11th December, 1831,
wherein they give the following brief summary of a series
of experiments made by the late Mr. Frank Forster upon
the anhject.
" On the 15th of July, 1851, a float was put into the
centre of the river, opposite Barking Creek, two hours
after high water. This time was chosen because it was
found that sewage discharged into the river two hours
before high water, arrived at about the same point above
Barking Cresk that sewage discharged two hours after
high water did by the next flood tide. At low water it
reached 11i miles below that point, and returned with
the next flood tide to one mile above it, having gone 12i
miles that flood, it being then the period of spring tides.
" As the neaps came on the float continued to work
lower down each succeeding high water, and by the 24th
of July it was 13 miles below Barking Creek at high
water, having gone down the river 14 miles during the
falling off of spring tides to neap tides. As the flood again
became stronger, it worked up the river each succeeding
tide until the 29th of July, when it again became within
five miles below Barking Creek at high water, having
worked up the river 9 miles from high water neap tides to
high water spring tides, the excess of the ebbs over the
floods being only 5 miles in 14 days.
" Another experiment was tried at the same place on
the 6th of August, 1851, it being then lowest neaps, and
the float being put down two hours after high water. It
worked up each succeeding high water till top springs on
the 12th of August, when it reached 6} miles above Bark-
ing Creek at high water. The float then again worked
down the river till the 20th of August, being neaps when
at high water, it reached 9i miles below Barking Creek,
being a distance of 16 miles, during the falling off of spring
tides to neap tides. The excess of the ebbs overthe floods
would, in this case, have been about 7 miles in 14 days.
The wind and other causes would vary the result ; but it
may be roughly assumed that a substance in suspension
works up the river about one mile a day each high water
as the springs strengthen, and down the 'river two miles
a day as they fall off.
" The main object was, of course, to determine how
near to London the sewage could be discharged into the
river at or near high water, without finding its way back
again to the inhabited parts of the town. The experiments
proved that it was essential to go as far as Barking Creek,
and also as regards the level of discharge, they demon-
strated that it should take place at or near high water as
practicable.'
" Now, although it is• desirable to fix the place of dis-
charge as far below the metropolis as possible, it will be
found that a practical limit to it is imposed by the neces-
sity of maintaining sufficient fall in the sewers to keep
them clean, and at the same time of preserving as a safety
valve a discharge into the river at low water by gravitation,
in case of accident to the pumps, as well as during exces-
sive floods. It must be borne in mind 'that the delivery
of the sewage at high water into the river at any point, is
equivalent to its discharge at low water at a point 12 miles
lower down the liver ; therefore the construction of 12
miles of sewer is saved by discharging the sewage at high
instead of at low water.'
"The position selected is Plumstead-marshes, and the
period of discharging the sewage into the river would be
from two to four hours nearest to high water.
" The amount of sewage proposed to be intercepted from
the more closely inhabited districts has been estimated
; upon data, which makes provision for the increase of future
generations.
"Thus, where the population, as at present existing,
exceeds 30,000 to the square mile, the actual numbers are
estimated for ; and where it is less allowance has been
made for that number, in order to provide for future in-
crease. The supply of water per head has been reckoned
at five cubic feet per diem, being on a more liberal scale
than now actually obtained ; and of this quantity it is
contemplated that one-half will pass away during six hours
of the day.
" For reasons more fully set forth in former repent, it
is proposed, in the urban districts, to intercept a quarter
of an inch of rain in 24 hours, which is at the rate of
about 100th part of an inch per hour ; any excess beyond
that amount, falling on occasions of heavy storms, being
discharged into the river by the drainage sewers.
" With a view to economy by the reduction of the sizes
of the sewers, as far as practicable, it is now proposed to
continue the drainage of all those portions of the suburbs
which are not likely to be built upon for many years to
come, into their natural valley outfalls ; and where build-
ing has already commenced, and is likely to be extended,
to provide for an increase of population varying from
10,000 to 20,000 to the square mile instead of 30,00 Tt
is further proposed, from the more thinly-peopled suburbs,
to carry off by the intercepting sewers only one-half of
the quantity of rain water for which provision is made in
the more crowded districts.
" The different areas drained, and the quaiitities pro-
posed to be intercepted, are stated in detail in a table ap-
pended to this report. (See appendix B.)
" The sizes of sewers, their inclinations, and their dis-
charging powers, under various conditions, are important
considerations in forming a drainage scheme. In the pre-
sent instance it is a matter of moment to economise the
fall so as to reduce the amount of pumping, and, as
far as practicable, to preserve safety outlets
into the river, and in order thereto to adopt
the minimum velocity sufficient to keep the seweis free
from deposit ; the velocity depending upon the fall in the
sewers of a given size. Upon this point Mr. Wickstead in
his report upon the drainage of Leicester (p. 19), states,
, ' From experiments made by me with great care, I find