202 
On the Salt- Water Lakes 
[July 
channel, receiving some little water from the great river, the tide, in its run up a 
long continuous channel, gradually spends itself by the length of its course and 
friction of the bed. 
It is a question of some difficulty in hydraulics to determine the level of the sur- 
face of the highest and also of mean tides in these jhils, or what may be called the 
point of dissipation of the creek tides, relatively with the highest level of the tides 
of the bay from which they are fed ; and when I hazard the assertion, that the 
point of dissipation is below the highest level of the parent tide, even at the dis- 
tance of 70 miles from the sea, which I believe to be the case universally, I na- 
turally do so with some caution, as the subject has not been considered by any 
mathematical writer upon the subject of tides. 
It is not my purpose to enter more particularly into the reasons that have led 
me to such a conclusion in this place 1 . 
The jhils above mentioned, and the salt lakes in the present case, from their 
depression below the general surface of the country, naturally become the recep- 
tacles of all its superfluous water ; and where this supply is considerable, the ge- 
neral level of the jhil, as also of the creeks which run up into it, is influenced in 
proportion during the season of such supply. In no case, however, does there exist 
a rise from such cause at all in proportion to the influence, in parallel latitudes, of 
the permanent freshes of the great river, when admitted into a branch like the 
Hoogly. The effect of such supply creates a general slope of the surface of the 
lake or jhil, proportionate to the expenditure required, and in the creek, which is 
the outlet of the Salt-water Lake for this expenditure, the summit level is found 
very little (not 1 foot) above its extreme summit level in the dry months, when 
only the tide of the sea enters it; and the discharge is then effected by an inequa- 
lity in the duration of the flood and ebb, in the same way that the freshwater of a 
river is carried off. 
The supply of fresh water which now enters the salt-water lakes is found to 
raise Us mean surface towards the centre or opposite Baliaghat 2 feet. This level 
is, however — which would not be at first supposed — still below the summit level 
of the tides of the sea. 
I have made the above remarks to explain particularly the nature of these back- 
water creeks, because in case of the obliteration of the lakes by their being filled 
up or embanked against the tide, and a canal connected with these creeks being 
brought in circuit round one half of the city to be drained, it is essential to 
know what will be the state of the tides tinder these new circumstances. Indeed 
the whole question of the expediency of recovering the lake for agriculture, as 
well as the means to be adopted for the purpose, will turn much upon this point. 
The first case to consider is — Supposing the removal of the lakes, and substitu- 
tion of a closed canal of the above nature to Chitphr ; what would he the effect 
tipon the present tide levels at Tarda, below the confluence of the lake outlets, 
and Tolly’s nulla ? Also to assign a position to the summit level of the present 
Tarda tides upon our general tide-gauge. 
Upon the general principle that the extreme level in a creek nearer the parent 
tide must be above the highest surface in the lake of dissipation when there is no 
foreign supply of jhil or rain water, and no supply into this lake but direct from 
the sea by this creek, I have supposed that the present extreme tide at Tarda in 
the dry season, April and May, is nearly the mark 4- 1 ; while the highest level near 
Baliaghat is at Q ) ; and that the extreme levels at Tarda and in the center of the 
lakes during the rains nearly correspond to -+* 2. Upon like reasoning it may be 
shown, that by withdrawing the influence of the lakes, the extreme level at Tarda 
will be raised a little ; but as the tide will have a lengthened canal in which to 
dissipate part of its force, (while all influence of the river is withheld,) the extreme 
tide can never exceed what it is at Tdrda at present, or + 1 in the dry months, 
unless the dimensions of the dhial are much enlarged. Its highest level in the 
rains will depend upon the method of draining the town, and the waters of the 
surrounding country into this outlet, as also upon the question hereafter to be 
discussed, whether any additional quantity of water is to be thrown in for filling 
the lake, and where its discharge is to be effected. 
The floors of the present Circular- Road drains have an altitude on our guage 
fit the respective places, as follows: ft. *• 
Head of Dhermtdlah, ^ + 2 1 
,, Bowbazdr, H fen % -j- 5 1 
,, Match uubaz&r, > ;g < -f- 2 4 
,, Maniktdlah road, 3 ^ 
,, Sa'mbaziir road 2 , 3% C. -j- 2 10 
1 4 ide notes on the Tides, published in former numbers of this journal. 
8 Marhatta Ditch. 
