Decline of Bhagirathi-Hooghly Channel - The Ganga: Water Use in the Indian Subcontinent - page 70

to the silt-load. The annual silt-load in the Hooghly, south of Haldia, is about
40-50 million cubic metres. Besides, because of continuous upland discharge
through the feeder canal, the ebb-tide in the river is continuously supplemented,
increasing the velocity of the ebb-tide and reducing the flow-tide. This has taken the
slack-zone from Santipur-Kalna reach in the pre-barrage days to somewhere below
Diamond Harbour in the post-barrage period where the silt-deposit has increased
manifold, obstructing the navigation channel. As a result, Jiggerkhali flat, upstream
of Haldia port, is expanding day by day and the navigation channel from Haldia port
to Kolkata is now totally blocked. Construction of a guide-wall on the upstream
of Nayachara island and other palliatives by the Calcutta Port Authority have
not been able to open up this navigation channel alongside Haldia. Fortunately,
the Rangafalla channel, opposite Haldia, has opened out and the navigation route
through this channel has saved Kolkata port. Until and unless this huge silt-load in
the navigation channel is cleared and further deposits prevented, the fate of Kolkata
port will remain unstable.
The gradual deterioration of the Bhagirathi offtake near Biswanathpur can be
explained by facts and circumstances. The offtake point has undergone a number
of changes in the last 200 years, which were due to eastward shifts of the loca-
tion from Dhulian, then Suti, then Geria and finally to Raghunathpur before the
construction of barrages at Farakka and Ahiran near Raghunathpur. Each one of
these changes assumed importance as long as they lasted. Their typical circum-
stances were associated with the opening of a new takeoff point as the former closed.
Throughout their tenures, offtake points shifted continually toward east and the sup-
ply of water accordingly diminished from the parent river. Whether this arose out of
alluviation at the heads, or from tectonic change of shifts in the remaining delta fol-
lowing change in the river courses in some place or other (i.e., the great shift of the
Teesta), or because of swing of the river to the east, are matters of debate. None of
these can, jointly, or separately, explain these unique phenomena of the Bhagirathi,
near its offtake point from the Ganga. Dhulian offtake point was probably near the
present Dhulian-Ganga railway station. Gradually, this offtake point, together with
the Bhagirathi channel, was engulfed by the Ganga. Disastrous bank erosion, caused
by high floods, between 1730 and 1740 is said to have given rise to the situation. At
present, the Ganga near old Dhulian offtake point is about 5 km wide with a 2 km
wide char island inside the river but the old Bhagirathi is nowhere to be seen. After
it closed, the offtake point shifted to Suti, about 10 km downstream. In the begin-
ning, the angle of obliquity of the off take point was probably acute, like that of any
other distributaries, which gradually changed to an obtuse angle before it finally got
choked. The remnant of the old channel can be seen here, even now. The next exit
was formed at Geria, about 10 km further down and the same process was probably
repeated, from acute angle to obtuse angle before it finally closed by silt deposition
at the mouth. The closure of this offtake was first noticed on 26th November 1919,
according to Basu and Chakravarty in 1972. Swamps, marshes and low pockets at
Geria are tell-tale signs of an old channel. The point then shifted to the present
location at Raghunathpur and the process repeated again. The mouth also gradually
silted, reducing discharge into the Bhagirathi from the Ganga. When the mother