floods the

low-lying parts

of the town to the

of several rents

depth

feet, and even, it is stated,re verse curtake place, and the sewage mixed with the

water flows up the sewers and into the sub-soil.

It also appears that the pumping power re*quired to empty the sewers is only competent to deal with

weather sewage, but not with the or flush water, so that when

dry

addition of rain

or flush water is present in the is and the the penstock sewers, pumping stopped is opened and the flow through the sewers is then

either rain water

Julian JP 4 dip I

dependent

NOVEMBER 1892.

Salt Lakes. present

SEWERS OF CALCUTTA.

THE

sewer

We have carefully studied Mr. Baldwin Latham's report on the Drainage of Calcutta, together with Mr. Kimber's notes thereon. Mr. Latham's reply and Mr. Kimber's rejoinder, which form a bulky and somewhat intricate of the sewerage of Calcutta, and of the measures which have been proposed to remedy its defects and to extend account of the

present condition

its benefits to the

"

added

The

area

existing only the

to carry off not the rainfall, street washalso but sewage proper, as well as the water and the sub-soil water, ings, sewers

intended

were

flushing and the tidal water. They are, therefore, of enormously larger size than is required for the removal of the sewage alone, and it is an inherent defect in their original construcused for

tion that the flow of their contents is influenced twice a day by the state of the tides. The general trend of these sewers is from the

Hooghly eastwards

to

fortunately happens

Lakes is

the Salt that

Lakes,

high

and it

un-

tide in the Salt

three hours later than high tide in the Hooghly. The result of this is that the flush water, entering the sewers during high some two or

tide in the

half

to

Hooghly

three hours

sewers, meets with

and

taking

to traverse

high tide

from one-and-alength of the

the

at the outfall towards

the Salt Lakes, and the consequence is stagnation in the sewers in the place of flushing; aud as

stagnation

deposit, the result is that self-cleansing, but have to be

means

sewers are not

and

the en-

deposited troop of boys, contents, chiefly road detritus, removed by hand. Not only is this the case, but when heavy rainfall tered

by

coincides, sewers

a

as

being

their

ifc often does with high tides, the occupied with sewage and tidal

water, the rain-fall is unable

on

to enter the sewers,

the level of the water in the tidal Another inherent defect in the

is, that the

sewers

is

higher

surface of

at the

tance from the outfall

of the

city

of the outfall

station than the

pumping

of the town at

parts

some

crown

works

; and

is to be effected

as

through

dis-

some

the

drainage

the outfall

sewer, it happens when this sewer is full that the lower parts of the city become a reservoir for rain and mixed sewage, which cannot until the sewers have been relieved by escape the comparatively slow flow from them. There

storing

is,moreover, a the

intended

constant

leakage going

aud the sub-soil.

sewers

to

necessarily

on

between

Sewers which

were

carry away the sub-soil water must be porous, aud the Calcutta sewers

are so porous that the leakage into t he sewers, which is constantly going on, varies, at different seasons of the year, from two to fifteen millions

of

in

gallons

the tides.

twenty-four hours, according

Now

considered

a

leakage

into the

sewers

positive advantage

if it

might

to

be

were never

It has resulted, as Mr. Kimber points out, iu lowering the level of the sub-soil water of Calcutta from 4 to 9 feet ; but when the with mixed sewage and rain sewers are reversed.

gorged

the facilities for for

leakage

leakage

in

are

to those the sub-soil

equal

out of the sewers, and

then becomes the resevoir for the mixed contents of the sewers, aud there can be no question that Such an interchange between the soil and the health. We cannot sewers is most dangerous to with Mr. Kimber in his opinion that the dilution of the sewage with eight times its volume of water can be regarded as in any way rendering concur

the sewage innocuous, and we agree with Mr. Latham that energetic means should be at once taken to remedy this evil. Mr. Latham gives which show that at certaiu seasons aud figures O in certain conditions of the tide the leakage from the

sewers

into the sub-soil takes

place with

INDIAN MEDICAL GAZETTE.

336

[Nov.

1892.

the high tides this low level outfall reservoir for both the sewage form a would Latham proposes that the existing sewers should water and rain flowing through the sewers, and be lined with bricks set in Portland Cement, and that 110 lime such as has been hitherto used in on the tide falling, the gate would be opened To

alarming facility.

the construction of the Calcutta be

ever

employed,

tliia

remedy

evil

sewers

Mr.

During

should and the contents discharged. It is almost inconceivable that have

constructed

been

should

sewers

because it is unable to with-

the

stand the action of the sewage, and all sewers principle should be set in Portland Cement mortar, or which is revealed in this correspondence?made with the intention that they should reconcrete. Clay, he says, should 011 no accouut porous the move sub-soil water as well as the sewage, be used to cement the joints of pipes, as it is liable at the and same time with au outfall higher than to shrink after it dries; and if it does not dry, it remains soft and plastic, and the weight falling 011 many parts of the town, so that the currents the sewers when they are " running full" the sewer trench squeezes it out and leaves ju be reversed, and the subsoil converted into openings at the top through which interchange may a storage of the contents of the the of soil contents gorged sewers, between the takes ever

on

O

place

and

the

It

sewers.

is,

essentially

moreover,

necessary that all sewers should be provided with valves at their openings into the main sewer to prevent reflux and reverse currents set up

being

leakage ing found are

110

stripped.

?which he

into the

sewers

sub-soil,

evidence of this when the But

Latham,

examined

joint leaking

Kimber denies the

within them.

from the

a

and the

011

one

was

evident

sewers

occasion

011

pipe sewer, found every pipes half full of earthy

matter washed into them from the

it

hav-

by comparing

with the tidal records of ever the tides are low and

the

outside;

sewer

and

gaugings

that when-

Calcutta, rapidly falling,

are

at

when

the flow in the that time of the day sewers is increasing, there is either a direct loss of the contents of the sewers or little gain. While on the other hand even at low water periods, if the tides are rising during the time that there is an increase in the flow within the sewers, there is a gain in the volume flowing within the latter. This constant

interchange

between the contents

of the

and the soil

seems

sewers

to us to be of

most serious and urgent importance ; and taking it into consideration it is 110 longer difficult to understand why it is that, while the health of

without valves

regurgitation

on the branch sewers to prevent and reversed currents; and that

non-hydraulic

lime

impossible for us provision of flushing

the

instead

sewers

reverse,

from

fever,

steady as

death-rate

shown in the annual reports of

the Health Officer. To obviate this difficulty Latham proposes to make the sewers water-tight and to facilitate

through them by providing a low level would be guarded against the which outfall, influx of the tides by a self-acting flood gate. the flow

to

enter, such

tanks

of the

general

tidal

flushing,

which commend themselves to a non-professional mind, but which involve technical encriueerincr CD '

O

questions

which

could not

we

profitably discuss;

but there are others which we should have liked Mr. Latham to have settled, such, for instance, as the disposal of the sub-soil Avater if the

present

proposes, for the

depends the

city

and

we

are

as

the

stands.

water-tight as he absolutely necessary

of Calcutta

salubrity 011

made

seems

purity On this

confess to

so

far

of the soil

question

having

found

as

that

on

which

he is

silent,

great diffi-

in

culty his

sewers

and

discovering any clear statement of of providing a low level outfall original report. It is only alluded to in

scheme

in his

paras. 30 and 38, in which the

new outfall works twelve aud-a-half lacs far from his seeming to have

estimated to cost

ment, there

the

withstanding

at the heads of all minor sewers, and that of sectional flushing gates in the interior of the larger as

are

increase in

of

into which it is

of rupees; and so originally intended

a

incapable

the effect of sewage should have been employed in their construction. There are other points

Calcutta has

undergone such marked improveespecially as regards cholera, of late years, is no similar diminution, but rather the

J

a

over

low level

to the additional cost of

outfall,

pumping

he alludes the whole or

part of the sewage a second time between the present pumping station and the proposed point of outfall. We cannot help thinking that the ?low level" portion of the scheme was an afterthought, else this which appears as the leading

feature of the scheme in the latter portions of the correspondence would surely have been more

Nov.

SEAMEN IN CALCUTTA.

1892.]

clearly stated. Such being the deprecate the discourteous, not to

case,

we

must

say contemptuous, tone of many of Mr. Latham's remarks as uncalled for and unjustifiable and in marked contrast with the dignified attitude assumed by

Mr.

throughout the someunpleasant correspondence our sympathies entirely go. All of this unpleasantness and Kimber,

with whom

what

misunderstanding might have been avoided if the original plan of a joint report had not been departed from by Mr. Latham. C5

O

337