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canal and the Bhagirathi. Its moribund channel and the tidal channel of the Hooghly
have been somewhat rejuvenated. Calcutta Port and the city got a fresh lease of life
following voluminous flow of sweet water. Much less than the required and agreed
quantity of 40,000 cusecs did pass, which was not enough to restore the navigation
channel to the 1935 condition. The overall effect of letting in the Ganga water into
the Bhagirathi-Hooghly navigation channel from 1978 to 2000, as against that of
1975, can be seen from the records of the Calcutta Port Trust, as summed up below,
in four periods.
i) Period from 1978 to 1982, covered by the 1977 agreement,
ii) Period from 1983 to 1988, covered by the MOUs of 1982 and 1985,
iii) Period from 1989 to 1996, covered by no. agreement, MOU or Treaty, and
v) Period from 1997 to 2000, under the 30-year Treaty of 1996.
The navigation channel can be divided into six parts:
i) Ahiron to Berhampur-108 km (upper reach of the Bhagirathi),
ii) Berhampur to Nabadweep-122 km (lower reach of the Bhagirathi),
iii) Nabadweep to Tribeni-82 km (upper tidal zone of the Hooghly),
iv) Triveni to Kashipur (Calcutta Port area)-63 km (lower tidal zone of the
Hooghly
v) Kashipur to Hooghly Point-63 km (upper estuary of the Hooghly), and
vi) Hooghly Point to Sagar Island-84 km (lower estuary of the Hooghly).
An index plan of the Bhagirathi-Hooghly is shown in Fig. 10.11. The effect of
the upland discharge on the two reaches of the Bhagirathi in terms of the aver-
age Hydraulic Mean Depth (H.M.D), its cubic capacity and the percent variation in
different years from 1975 (pre-barrage period) is shown in Table 10.10.
The table shows that the effect of upland discharge on the upper reach of the
Bhagirathi is far better than in the lower reach. The average depth increased by
Table 10.10
Effect of Ganga discharge on the river Bhagirathi at dominant stage level
Upper reach (108 km)
(Ahiron to Berhampore)
Lower reach (122 km)
(Berhampore to Nabadwip)
Cubic
capacity
(post-
monsoon)
(10
6
m
3
)
Cubic
capacity
(post
monsoon)
(10
6
m
3
)
Percentage
variation
(+)/(-)
w.r.t.1975
Percentage
variation
(+)/(-)
w.r.t.1975
Percentage
variation
(+)/(-)
w.r.t. 1975
HMD
(average)
(m)
HMD
(average)
(m)
Percentage
variation
Year
1
2
3
4
5
6
7
8
9
1975 4.37
-
98.20
-
5.10
-
187.20
-
1982 5.92
(+)35.50
114.40
(+)16.50
4.85
(-)4.90
190.00
(+)1.50
1992 5.49
(+)25.60
128.00
(+)30.30
5.07
(-)0.59
199.60
(+)6.62
1996 6.09
(+)39.40
140.90
(+)43.50
5.15
(+)1.00
192.60
(+)2.88
1998 5.63
(+)28.80
129.20
(+)31.60
5.10
0.00
194.00
(+)3.63
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