Geoscience Reference
In-Depth Information
As desired by Prof. Hensen in 1957, the Hydraulic Study Department of the
Calcutta Port Trust undertook studies on increase of siltation in the Hooghly, grad-
ual decline of bars and crossings, increase of tides, salinity, fall in the water volume
etc. and sent the findings to him and also submitted to the Government of India
for reviewing the need of fresh water supply in the river for its resuscitation.
Prof. Hensen visited Kolkata in 1966 and 1977, reviewed the collected data and
came to the conclusion that the minimum requirement would be 40,000 cusecs. He
told the Director of the River Research Institute, Kolkata, the Chief Engineer of the
Farakka Barrage Project and the Chairman and technical officers of the Calcutta
Port Trust that in the first half of May 1957, provisional discharge requirement was
at least 20,000 cusecs, not less as interpreted by an erroneous translation of his
German report. He studied the fresh data and revised the requirement upward to
40,000 cusecs as the minimum in dry months.
The RRI, a State Government outfit, carried out independent investigations by
studying regime relationship of tidal inlets and prototype data and came to the con-
clusion that a maximum of 40,000 cusecs was required in dry season to obtain sta-
bility in the port reach. Studies were also carried out by Dr. D. V. Joglekar, Director
of the CWPRS, Pune, A. C. Mitra, Chief Engineer (Irrigation) of Uttar Pradesh,
Dr. J. J. Dronkers, Chief of Hydraulics and Research, Netherlands Government,
Dr. K. L. Rao, India's Minister of Irrigation and Power and Debesh Mukherjee, the
first General Manager of the Farakka Barrage Project.
Views of Indian Experts
Dr. Joglekar studied the siltation above Kolkata and the downstream shift of
the effective barrier and thus of tidal energy and said in his report, dated
22nd January 1968:
Loss in capacity above Calcutta has resulted in the increase of ranges
...
of flood currents
in the dry season and incidental increase of re-distribution of sand in the dry season in the
port reach, causing progressive loss of navigable depths.
Studies by him to evaluate the pattern of energy losses from the observed simul-
taneous spring-tide gauges, reach by reach, showed that in 1917, the peak losses
occurred in the Chinsurah-Dumurdaha section, 40-60 km above Kolkata but in
1955, the region of heavy losses moved down to Calcutta-Konnagar reach within
12 km of the port. This downward shift of peak energy losses was due to down-
ward movement of effective barrier and hence to the decline of tidal propagation.
Increase in the frequency of bore tides in recent years also confirmed this. He was
confident that with 40,000 cusecs from the Farakka Barrage and by adopting mea-
sures, mentioned above, the Hooghly can be restored to its 1936 condition. Though
the required discharge had been assessed at 46,000 cusecs, Dr. Joglekar did not con-
sider that this reduction of available discharge would have any adverse effect, as the
supplied water would be relatively silt-free.
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