Only a Barrage Can Save! - The Ganga: Water Use in the Indian Subcontinent - page 85

Photograph 7.3 Congestion of ships in the King George's Dock during the bore tide restrictions
in the port of Calcutta
occurred to the south of this section, between Garden Reach and Konnagar which
is 9 nautical miles north of the city; the loss in the latter was 24.6 times more than
in the former. This southerly movement of peak losses is a cause of deterioration
of tidal and navigable status of the river and of removal of the barrier effect to
improve tidal propagation. Hydraulic model studies by the Central Water and Power
Research station, Pune confirmed the findings. Higher energy losses above Kolkata
were gauged from special measurements of low water which showed that in a dis-
tance of 18.7 nautical miles, between Mayapur and Garden Reach, the low-water
rose by about 0.35 m, while in a comparable length above Kolkata, it was three
times more.
It follows, therefore, that to improve tidal propagation, the upper tidal compart-
ment has to be improved. A scrutiny of depths and bore tides in 1935-1936 showed
that in these respects, the Hooghly was better with a depth of over 9 m in the port
area and on low-water crossings it was over 6.5 m, when the governing Balari bar
was at its best. Though incidence of bores was more than in 1920, it was much less
than at present. Thus, it was desirable to bring the river back to the 1920 condition,
or to the second best condition in 1935-1936. To achieve this, the only possible ways
could be (a) dredging the channel and dumping the spoils ashore, and (b) helping
Nature to carry the silt-load to sea.
The reach above Kolkata needs about 3.35 million cubic metres of silt-dredging
in a year and the reach below it up to Diamond Harbour needs about 3.40 million
cubic metres but there was shortage of space for dumping spoils. Besides, dredging
was not a permanent solution even with river-training unless the sand-drift features
are reversed so that sand would not come in the navigation channel and the port
area. Therefore, the only alternative was to optimize the head-water discharge.
Kolkata's need of drinking water is met by drawing from the Hooghly at Palta
in south 24-Parganas, about 24 km north of the city, where a pump was installed