Decline of Bhagirathi-Hooghly Channel - The Ganga: Water Use in the Indian Subcontinent - page 68

June 1865, reviewing the general hydraulic factors in maintaining the river channels
and the conditions at the critical points for investigation. He agreed with the majority
of the 1853-1854 Committee that the Hooghly would certainly deteriorate, howso-
ever slowly, because of the agencies at work. The enormous quantity of silt, carried
down every year, would be deposited in, or about, the debouche, lengthening the
sand-heads and thus decreasing the scouring power of the stream.
In the latter part of the 19th century, traffic and trade in Kolkata port increased
gradually and vessels of larger size and bigger capacity with more draft frequently
visited the port. In 1853, the largest vessel to berth was 1810 tons' capacity. This
steadily increased and in 1917, the biggest vessel that visited the port was of
12,989 ton capacity. The length and draft of vessel also increased from 368 feet
in 1870 to 511 feet in 1917. Between 1830 and 1913, the draft increased from 17 to
28 feet but because of restrictions by the port authority, the pilots were not allowed
to travel with vessels of more depth between Kolkata and Diamond Harbour. In
1830, a rule was revised to strictly forbid pilots, on threat of dismissal, to ply a
vessel of more draft than 20 feet at any time of the year, even with the aid of compe-
tent steamers. Vessels with more draft had to discharge part of their cargo either at
Sagar, or at Diamond Harbour, where transit facilities existed. In 1912-1913, before
the 1st World War, 49 ships of over 27 feet and 12 of over 28 feet draft plied on the
Hooghly. However, the increases in size and depth of vessels were not so much due
to hydrological and hydrographical improvements in the navigation channel as to
the change in the design of the cargo vessels and ships as well as to increase in port
facilities. The navigation channel deteriorated owing to siltation in spite of increase
in traffic and dredging as well as other measures, adopted to maintain the draft.
From Kolkata to sea-face, 14 submerged sandbars exist, spread over, more or less,
the entire cross-section of the river in different orientations which change according
to seasons. Because of siltation, these also gradually choked and created more haz-
ards for navigation. These bars needed constant survey and dredging to keep clear
the passage of ships to and from Kolkata port.
To sum up on the basis of these opinions as well as causes and extent of deteri-
oration of the Bhagirathi-Hooghly and according to records of Calcutta Port Trust,
in olden days, it was the mainstream of the Ganga. It was through this channel that
the Ganga found its way to the sea. From the 16th century, the Ganga tended to flow
more and more through its eastern arm, the Padma across Bangladesh to flow into
the sea. Because of heavy siltation in the mouth and reduced depth, the Bhagirathi
drew less and less water into it, causing more and more siltation over its bed and
the mouth. The bed of the mouth rose gradually and the mouth moved from Dhulian
to Biswanathpur by 1950. The flow through it was possible in only three monsoon
months and for nine remaining months it remained high and dry. The mixture of
clay, silt and sand that enters the Bhagirathi with the Ganga water during monsoon
months could not be flushed to the sea through the choked mouth, because of weak
current after the rains. On the other hand, tides push this silt up and leave deposits on
the bed. The sands deposited near the receiving end help disconnect the mouth from
the Ganga and push the stream eastward. It also raises the river-bed, gradually. In the
Hooghly, though the diurnal tides are evenly distributed below Saugar Island for 5 h
daily, the situation is different near Kolkata. The flow-tide endures about 25% less