1830 .] 
in the vicinity of Calcutta . 
203 
These will allow of the drainage remaining without alteration, as long as 
the water in the canal does not reach above -f* 3 during the season of rain. 
It is therefore clear, that the lake’s being withdrawn or embanked, will not embar- 
rass the drainage of the town, although the circular canal brings the Sundurbun 
tides in immediate contact with the drain outlets. It remains now to provide 
for the maintenance of the same level of ■+■ 3 during the rains. 
llie klke remaining as it is, and no water being admitted from the river, the 
highest level on the canal, except from the small influence of drain water from 
the town, will not exceed -f- 2, and can scarce reach that mark 3 ; and this influ- 
ence ot town drain water I consider will never, even in flowing tides, raise the 
Chitpur end ot the canal more than 1£ foot under any circumstances. 
It must now be considered that the drains, with the exception of the Dlierm- 
tolah 4 , under the new circumstances of being so much nearer tlieir outlet, will 
have great advantage ; and as the lowest spot in Calcutta is much above® the 
highest ot these drains, there will be rather an advantage than otherwise in now 
and then allowing the tide to enter their mouths. 
I may therefore safely assume, that any scheme may be adopted which will not 
raise the waters above -I- 3 during the rains; and that under the contemplated 
circumstances, an additional level ot a foot may thus be given to the surface of the 
ake, tor the purpose of raising its bed with sediment, without danger to the 
drainage. ° 
Salt-water Lake adjoining Calcutta, covers a surface of 18.5 square miles 
and. from its lowness in level it is at present the receptacle, during the rains, of 
the waters of a considerable surface of country, besides the more immediate drainage 
e city ot Calcutta. The principal influx of water is from the north and west ; 
and m the rains, when this is at a maximum, there is an evident general slope of 
le surface of the lake proportionate to this expenditure, which has been detected 
by the several series of levels which have been carried on at different periods. 
ie surface of this lake is naturally divided into three compartments : two north 
of the present navigable 3 channel and lake outlet ; a third south of that channel. 
Of the two first, the western, containing 5.5 square miles,- at present receives the 
greatest influx of extraneous water from the north towards Dumdama and wesC 
from Calcutta ; but neither yields so great a depth of water, nor presents to the 
eye so great an expanse free from vegetation as the neighbouring compartment 
of 7 square miles, which is separated from it by a natural rise in the bed upon which 
vegetation has taken root, although the surface is almost at every tide under water 
The surface of the upper end of the first named compartment towards the 
Sambazar bridge, is said by Major Sell alch to have an elevation of 2 feet above 
what I have ascertained to be the extreme level near Baliagh&t, which would 
give a slope ot / inches per mile to the surface. Now as I know this elevation to be 
very partial, and owing to a certain admission of tide by the Sambazdr ditches’ r 
must reject such a slope, as at variance with every other observation I possess relative 
to its slope, and particularly the velocity of its waters, which certainly never attain 
to any thing near what would obtain with such fall 8 ; and I believe I shall be within 
, “? ark in assigning a slope of 3 inches per mile as an extreme to the surfW 
of this compartment during the rains, generally from the Sambaz^r enclosure 
the Baliagh&t c/wkis . The expenditure in this case becomes II 6' 12 080 cubic feet 
* A ml 1 1 ’JP 011 y S( l n are miles of the town will give II 616 000 cubic feet of 
water The canal discharge per hour, when sloping 6 inches per mile, will be 4 nna 
cubic feet. It would never be necessary to drain off an inch of water in less link? 
S « 'mm cZ a t\ h ;eTht b : mB raised ,0 9 inches pcr the «»«»». “ill 
uof wo'rbVfe^r/^r 8 ,o do n,ore at 
5 Lowest part of Calcutta at the mark -f. 8ft. Q in. on the gauge. 
« Area of the Western, 5.5 square miles. Eastern, 7 ditto. Southern, 6 ditto Total 
18.5 square uules. } lu> 
Major S -, t00 k ‘his level under the bridge, and neither allowed for the run of one 
enclosures^ 6 e “ closares ° f the lake, nor the afflux in passing through these 
* The section being 15840 square feet, or 5280 x 1.5 X 2 = 15840. 
\ = | rate becomes 1213 feet, or about $ mile per ), our> 
