increase of expense in building semicircular bottoms?—None; and if the
sides are curved also it forms the stronger sewer for the same expense.
How are the sides of the sewers generally built?—As far as I am
informed, they are built with upright walls. I know none but the new
sewers in the Holborn and Finsbury divisions that are built with curved
sides, though I have no doubt that if any new sewers are built under the
superintendence of Mr. Walker, who is president of the Engineers’
Society, he would build them with curved sides.
What are the disadvantages of the flat-sided sewers?—They are not
calculated to afford the greatest strength. In clayey or slippery
ground, where there is a pressure on the sides, they are more easily
forced in. I have myself seen instances where expensive sewers have been
forced in at the sides. The curved side gives the strength of an arch in
resisting such pressure.
Is there any addition of expense in the construction of such forms of
sewers as you describe?—Less expense; there is less brick-work required.
As compared with some upright sewers with footings, the difference will
be two shillings in first size sewers, and four shillings per foot
lineal in sewers of the second size, in favour of the curved sewers.
In respect to the levels, how have you found the sewers?—They appear to
have been entirely constructed with reference to the locality, to drain
to the nearest outlet, and not on an extended view for the whole
district, or with any view to sewerage on a large scale. In the Holborn
and Finsbury divisions the Commissioners now adopt a series of levels
suited from the lowest outlets to the surrounding districts.
Have you heard of any alterations made in the surrounding districts on
the same principle?—I have heard of none as adopted generally. The City
have lowered several of their outlets; and Mr. Donaldson, on the
Westminster, has had the subject under consideration for some time.
What are the chief effects of the piecemeal town drainage without
reference to extended levels?—Chiefly that when new lines of houses are
built and require new sewers, either the old sewers must be taken up and
re-constructed at a great expense, to adjust them to a new and effective
sewerage, or the new sewers, if they are adjusted to the old ones, are
deficient in fall, and they have greater deposits.
Does the existing form or system of sewerage answer fully and at the
least expense the chief objects of sewerage in house and street
cleansing, and the removal of noxious substances?—No, it does not,
except where the outlets have been lowered, and the sewers continued at
a proper level; great accumulations of deposit are occasioned in the
sewers, and from their containing the refuse that was at one time
deposited in the cesspools, the deposit is more noxious than formerly;
the gas is more considerable, it escapes more extensively into streets
and into the houses, where the drains are not well trapped. My opinion
is that the general health of the men who work and have been accustomed
to the sewers, has become still worse; they are more pale and thin, and
lower in general health than formerly. The effect of the noxious gases
upon men working in these places is to lower the general health. Since I
have had the superintendence of the sewers, the men have encountered
about half a dozen accidents by explosions of gas.
But is the health of these men who work in the sewers to be taken as a
criterion of the health of persons who are not accustomed to such
places?—I have had no means of forming a comparison, though I am of
opinion that gases which they encounter without any immediate injury
would be very injurious to the health of susceptible persons, or of any
persons not habituated to it.
The first prejudicial effect of the defective system, then, is to
occasion these noxious accumulations; how are they removed?—Formerly, in
the Holborn and Finsbury sewers, and at present, I believe, in all other
sewers, the streets were opened at a great expense and obstruction (they
are so now, I believe, elsewhere); men descend, scoop up the deposit
into pails, which are raised by a windlass to the surface, and laid
there until the carts come; it is laid there until it is carted away,
sometimes for several hours, to the public annoyance and prejudice. The
contract price for removal from the old sewers without man-holes was
11_s._ per cubic yard of slop removed; where they have man-holes it was
6_s._ 10_d._ per cubic yard. This practice also involves injury and
expense as respects the pavement; a street may be well paved when it is
broken up for the cleansing of the sewers, but the portions of pavements
so disturbed are never so well put down again; neither can accidents be
effectually guarded against.
By what means may these effects be obviated?—In the Holborn and Finsbury
divisions I suggested a plan of flushing the sewers, and of carrying off
all the refuse by water. This plan has been adopted, and it is now in
operation. The breaking up of the streets is avoided by the formation of
side entrances; cast-iron flushing gates are fixed in the sewers; the
ordinary flow of water in the sewers accumulates at these gates; the
gates are opened, and the force of the water is sufficient to sweep off
the deposit; and the system may be further extended.
What is the comparative difference in the expense of construction?—The
cost of side entrances and flood-gates, as compared with the cost of
man-holes, is from 6_d._ to 1_s._ less per foot lineal of the length of
new sewers.
What other expense is attendant on this improved practice?—The main
expense is the attendance of a man to shut and open the flood-gates.
The structural expense being lower, is the ultimate expense of cleansing
lower also?—Yes; the expense of cleansing the sewers is about 50 per
cent. less than the prevalent mode. Our expense of cleansing the sewers
was about 1200_l._ per annum; we save 600_l._ of that, and expect to
save more; but to this must be added the saving to the public of the
cleansing of the private drains, formerly choked by the accumulations in
the sewers. This saving, on a moderate calculation, is found to be
upwards of 300_l._ per annum. There is also the diminution of the
escapes of gas from the old and continued accumulations.
During what intervals are deposits allowed to remain on the old
mode?—The average is in one set of sewers about five years, and in
another about ten years.
During which time the public are subjected to all the escapes of gas
from the decomposing accumulation?—Exactly so. It could not, however, go
on so long but for heavy falls of rain or snow, which occasion partial
clearances.
What is the effect of these accumulations upon the private
drainage?—That the drains to the private houses are stopped: the first
intimation of the foul state of the main sewer arises from complaints of
individuals whose drains are affected; the accumulations in the private
drains also occasion an expense to the individuals and much annoyance.
By flushing the sewers this expense might be, and in the Holborn and
Finsbury division it is, avoided.
Might not the price of sewers be reduced even below those you have now
in use, the egg-shaped sewers?—With the radiated bricks, I think that
the same capacity of sewerage may be secured with less thickness of
brick-work. I have given in an estimate of second-class sewers at 10_s._
6_d._ per foot lineal; which is 7_s._ 6_d._ per foot less than the
common flat-bottomed sewer with footing.
In these main drains a man may go up to examine them. Admitting them to
be necessary for the large towns, might not a smaller and less expensive
drainage suffice for small towns and villages?—There are situations in
courts, alleys, and small streets, where a less expensive form of
drainage would suffice. In fact 18–inch drains for short lengths,
costing, if made of radiated bricks, 4_s._ 6_d._ per foot, would
suffice; they would act well in proportion to the goodness of the falls.
Have you found the system of cleansing the large drains by flushing with
proper supplies of water equally applicable to small drains?—Yes,
equally applicable. A gentleman has tried it on a private drain of
18–inch capacity, and 1200 feet length, and it answers equally well. It
is cleansed by the collection of refuse water from 30 or 40 houses.
Might not the drains from private houses be also cleansed in the same
mode?—Yes, they might have a small and cheap apparatus for carrying away
all ordinary refuse. If in the small drain a brick fell in, it could not
be removed by the force of the small quantity of water which could be
obtained in such a situation. In our large sewers the heads of water are
in some cases strong enough to sweep away loose bricks.
Would it not be of advantage to the occupier, if the private drains were
under the same general superintendence?—I conceive it would in
management. They are frequently put to great expense by getting persons
to attend to them who really do not understand them. They are often now
obliged to have recourse to the contractor’s men. Private property is
often drained through other private property, and when the drains are
choked, if the parties are not on good terms they will not allow each
other facilities for cleansing. Under the Finsbury local Act there is a
power to enforce the cleansing of private drains, and by way of appeal
that power is sometimes resorted to by private individuals.
May we not presume that the same principles of hydraulics, as to the
advantages of a flow over a semi circular bottom, are as applicable to
small drains as to large ones?—More so from the flow of water being
smaller; the greater necessity for keeping it in a body to enable it to
carry away the common deposit.
Then there is a proportionate loss in having the private drainage made
with flat-bottomed bricks or boards?—Yes, there is proportionate loss
from the extra cost of cleansing. Semicircular drains of tiles would be
better, and cheaper than brick, for private houses.
Are there any other defects you have, as an engineer, noticed in the
prevalent mode of constructing the sewers?—Yes, the prevalent practice
is to join sewers at angles, frequently at right angles; this occasions
eddies and deposits of sediment that would otherwise pass off with the
water; it injures the capacity of the main sewers by obstructing the
current of water along them: I ascertained by experiment that the time
occupied in the passage of an equal quantity of water, along similar
lengths of sewer with equal falls, was—
Seconds.
Along a straight line 90
With a true curve 100
With a turn at right angles 140
The Commissioners of the Holborn and Finsbury divisions agreed to
require that the curves in sewers, passing from one street to another,
shall be formed with a radius of not less than 20 feet; it is also
required that the inclination or fall shall be increased at the
junction, in order to preserve an equal capacity for the passage of
water, and of effect in sweeping away the deposit.
When by heavy falls of snow or otherwise the refuse of the streets is
carried into such sewers, is there any difficulty in sweeping it
away?—None whatsoever.
How are the gully-holes or entrances to the drains affected by such
deposits?—Under the prevalent system the gullies and shoots are formed
so as to retain deposit, on the principle that it is cheaper to get the
deposit out of those than out of the sewers. The Commissioners in
Holborn and Finsbury, having adopted the flushing principle, have also
adopted a new description of gully and shoot, which I proposed to them
for the purpose of conveying the whole of the deposit into the sewers;
it is then washed away by the flushing.
In what number of years would the saving in cleansing sewers by flushing
repay the expense of applying the apparatus to the existing sewers in
the Holborn and Finsbury divisions?—In seven years.
What would be the expense of the construction of chimneys to remove the
foul air from sewers?—The expense would depend upon the sort and form of
chimney that might be used. A suggestion of Mr. Stable, one of the chief
clerks of the Holborn and Finsbury commission, appears to meet the case
at the least expense. He suggests that the pipes used to carry off the
rain-water from the roofs of houses should be connected with the crown
of the sewers; thus forming a chimney for carrying off the effluvia from
the sewers, and also a conveyance for the rain-water into the sewers.
The cost of connecting one such pipe with a sewer would, on an average,
be about 3_l._ 16_s._ 2_d._
Have you any doubt of the practicability of carrying all the surface
cleansing of the streets into the sewers, and removing it by conveyance
in water, as was proposed at Paris, instead of by hand labour and
cartage?—I entertain no doubt whatever that it might be done, where
there is a good sewer and proper gully-holes and shoots; with a good
supply of water these would carry away rapidly all the surface refuse;
the experience of the sewerage in the Holborn and Finsbury divisions
prove it.
How does it prove it?—At every opportunity the street-sweepers sweep all
they can into the gully-holes, and it is swept away without
inconvenience.
One practical witness states that the expense of the cartage alone of
the refuse from a Macadamised street of half a mile, in the winter time
in the metropolis, is 5_l._ weekly. What would be the comparative
expense of carrying it away by the sewers?—It would save the whole
expense of the cartage; it would be less than the present expense of
sweeping and filling into the carts, and if there were a sufficient
supply of water on the surface, the work might be conducted with great
rapidity.
You are aware that one inconvenience of the existing mode of street
cleansing, independently of the great expense, is the length of time
during which the wet refuse remains to the public annoyance on the
surface, until removed by the slow process of sweeping and cartage?—Yes;
and the men would appear to delay for the purpose of the dirt being
removed, by being washed by rain into the sewers.
Do you conceive that all the business of street cleansing and house
draining might be consolidated advantageously to the public?—Yes,
clearly so, and with great economy.
Have you, as an engineer, had experience in road construction?—Yes, I
have, having taken the levels and surveys preparatory to an Act of
Parliament being obtained for lowering the Long Compton Hills in
Warwickshire; I afterwards constructed the new line of road on Mr.
Telford’s principle.
Considering the drainage of a new district: the under-drainage of the
roads and houses and the surface cleansing, would not the public gain by
putting the drainage, the road-construction, repair and maintenance of
the roads, under the same management?—Yes, the public would get it done
much better by one surveyor and one Board than by two. In the old
districts, besides the double expense of officers, inconveniences arise
from the want of unity between the contractors for the paving and the
contractors for the drainage; there is always conflicting interests
between the two, and the work is not in many cases done with the economy
and expedition which would be practicable.
If the public, who may be ignorant of the science of sewerage and of
what it may accomplish, make no complaints, and do not agitate for the
adoption of any improved system, in how long a time do you think the
improvements demonstrated in the Holborn and Finsbury divisions would
reach the other end of the metropolis by the force of imitation and
voluntary adoption?—From the apathy shown and prejudice against anything
new, however valuable it may be as an improvement, and the various
interests affected, such as the contractors for cleansing, I do not
expect that they would become general in the metropolis during my
life-time. The public are passive, and the adverse interests are active.
You know the description of persons engaged as surveyors of various
descriptions in the rural districts and in the smaller towns?—Yes, I do.
Unless care be taken, is it to be apprehended that any new expenditure
will be made on imperfect and unwholesome drains with flat bottoms and
on false principles at a disproportionate expense?—Undoubtedly, except
they have to act on rule, it will certainly be so throughout the
country. The drainage that I have seen in the country districts is worse
than in the metropolis.
Have you found the sewerage produce any effect in the drainage of the
surrounding land?—Yes, we have found it lower the water in the wells,
often at great distances. For instance, in forming a sewer in the City
Road we found that it lowered by four feet a well nearly a quarter of a
mile distance. The only remedy we could advise to the parties was to
lower the well: they did so. We afterwards had occasion to lower the
same sewer three feet, when the well was lowered again in proportion; so
that the construction of the sewer, in this instance, drained an area of
40 or 50 acres on that side, and perhaps further. The water is sometimes
in such quantities and so strong in the land springs as to require
openings to be left in the side of the sewer for its passage.
Are there any fees taken in the Holborn and Finsbury divisions?—None.
Do you think the system of the payment of officers by fees
objectionable?—Yes, highly so.
“Have you met with instances where the drains have not acted, owing to
the inadequacy of the supplies of water?—I have not had my attention
called particularly to any private drain, so as to notice whether it did
not act owing to an inadequate supply of water, but taking the question
on the broad principle of the effect of a sufficient supply of water to
drains or sewers as beneficial in keeping them free from deposit, I beg
to state that I have noticed the effect on sewers of the same form and
having the same fall or inclination, and I have found that where there
has been an adequate supply of water no deposit has remained in them,
whereas where the supply of water was inadequate, deposit has
accumulated so much as to render cleansing necessary in a few years: the
effect must be the same in private drains.”
[Figure 1 is a representation of the form of the common sewers built in
the Westminster division. It is a transverse section, representing, on a
scale of a quarter of an inch to a foot, a sewer of the larger sort, the
greatest height being five feet six inches and the width three feet. The
smaller sewers are made of the same form, but only five feet high and
two feet six inches wide. It chiefly differs from the more common form
of sewers in not having a perfectly flat bottom.
[Illustration:
_Fig. 1._
]
The following figures, 1, 2, are representations of the sewers in the
Holborn and Finsbury division of the metropolis, on the same scale as
the above. The part in which the joints are marked in the cut is,
according to the directions, to be worked in blocks with cement.
[Illustration:
_Fig. 1._
]
[Illustration:
_Fig. 2._
]
The sides of these sewers form the curves of large radii struck from the
centres on the lines _a_ _a_, the radius for the larger size being about
13 feet, and that for the smaller size in proportion.
The spaciousness of the sewerage in the Westminster division of the
metropolis has been an object of pride; and it is stated that the
commissioners have walked in procession down one main sewer prepared for
the purpose. It was the glory of Rome that some of its cloacæ were so
large that boats and chariots might pass through them. All this,
however, appears to have been mistaken in principle, and in ignorance of
the mischiefs of the generation of gases and of the principles of
hydraulics, and their application for the attainment of the objects in
question. Mr. Smith, of Deanston, who has introduced the greatest
improvements in land drainage, advances the general principle, that the
size of sewers should be so adjusted as to have them always as full as
possible, with a quick flow; and he contends that the drainage of a city
might and should be so constructed as to give rise to as little occasion
for men to go through the main drains as there is for men to go through
the main pipes for conveying supplies of water. He would make the drains
narrow. “Their transverse section should exhibit an oval or egg-shape,
having the vertical diameter at least double the length of the
horizontal. The bricks used should be made on purpose, with radiating
sides.” “Care should be taken to make the building water-tight and
air-tight, and to prevent the foul water and effluvia passing into the
contiguous soil. Where land drainage is to be received, special openings
can be made at intervals to receive it. All private drainage should pass
into the sewers under ground by well-secured channels or pipes. Strong
clay pipes, of an oval section, hard burned, and with a good arrangement
for secure jointing, might be cheaply procured for the purpose.” It may
be said that there is scarcely any drainage, even in the opulent
districts, that at present meets these conditions. E. C.]
2.—_Evidence of_ MR. JOHN DARKE, _Contractor for Cleansing, as to the
Obstacles to Cleansing, and the Conversion of the Refuse of the
Metropolis to Productive Use_.
What are the practical difficulties you find in the way of the cheap
cleansing of the streets and houses of the metropolis?—The great
difficulty of the cleansing of the metropolis arises from the want of
proper receptacles for the filth. There is no filth in the metropolis
that now, as a general rule, will pay the expense of collection and
removal by cart, except the ashes from the houses and the soap lees from
the soap-boilers; and some of the night-soil from the east end of the
town, where there happen to be in the immediate vicinity some
market-gardens, where it can be used at once, without distant or
expensive cartage. The charge for removing night-soil from the poorest
tenements may be about 1_l._ per tenement. One house with another, the
expense may be said to be in London about 10_s._ per year, as the
cesspools may be emptied once in two years. One house with another they
will not produce more than a load of refuse from the cesspools, which,
not being composed, there is great absorption of the liquid refuse. I
have given away thousands of loads of night-soil; as we have no means of
disposing of it, we know not what to do with it.
What is the distance from the metropolis at which refuse is used?—The
expense of cartage of course increases with the distance. The average
extent of use of it as deposit does not exceed three miles from the
Post-office district in the city of London. Some night-soil has been
dried, packed up in the returned sugar hogsheads, and sent to the West
Indies for use as manure.
Is it not conveyed away from London by canal?—We do not at present, but
it might be. There is a penalty in the local Act of 5_l._, for
depositing it on the wharf.
Cannot you convey such manure by railway?—No, there is no mode of
conveyance provided. The charge, I believe, is a halfpenny per mile, but
that is for the use of the rails only; and the company do not favour the
transit of manure, and the farmer or contractor who would convey it must
provide engines for himself, which again would not pay. Night soil has
not yet been used systematically, and there are no places provided for
its reception.