Agreements & MOUs - The Ganga: Water Use in the Indian Subcontinent - page 204

more than 39% up to 1996 and thereafter, fell to about 29% in 1998. The cubic
capacity increased by more than 43% in 1996 and thereafter, fell to about 32% in
1998. However, in the lower reach the effect of discharge has been less. The average
depth increased by about 1% up to 1996 and thereafter, remained same. The gradual
reduction of depth from 1996 could be due to the effect of the Treaty, under which
the flow has been fluctuating every 10-day in the lean season. The change in cubic
capacity in the lower reach was not significant.
The impact of upland discharge from Farakka on the third reach of the river
(upper tidal reach of the Hooghly), in terms of its cubic capacity in both high and
low water level is shown in Table 10.11.
The table shows that the condition of the Hooghly reach from Nabadweep to
Triveni had been deteriorating in pre-barrage days. The analysis of cubic capacity
shows that it decreased from 157 to 148 million cubic meters at High Water Level
(HWL) between 1974 and 1975, but in spite of induction of upland discharge of
40,000 cusecs from April 1975 and 1977, the reach did not improve. The cubic
capacity showed decline by 8-10% at high and low water levels. Improvement was
not expected so soon, as the silt load that was moving down, did not have enough
time to move further down and get deposited in this reach. Had there been sufficient
discharge of 40,000 cusecs for a longer period, the silt load could move further
down gradually, leaving the Port area to the lower estuary region. This did not hap-
pen owing to fall of lean-season discharge from 1978 as per the previous year's
agreement. A part of the silt load, following the scouring of the Bhagirathi bed,
had also deposited in this reach. This process continued up to 1982 and thereafter,
as shown in the table. Though the condition improved in 1987 and 1996 over the
earlier years, it could never be even that of pre-barrage days of 1975. The improve-
ment was due to the creation of silt-trap zones by yearly dredging of about one

Table 10.11 Effect of Ganga discharge on the upper tidal compartment of the Hooghly (Nabadwip
to Triveni)

Cubic capacity (10 6 m 3 )

Percentage variation
w.r.t. 1975 (+)/(-)

Percentage variation
w.r.t 1975 (+)/(-) Year H.W.L. L.W.L. Remarks

1 2 3 4 5 6

1974 157.0 - 134.0 - Overall adverse effect

on the reach.

1975 148.0 - 127.0 -

1977 136.0 (-) 8.10 115.0 (-)9.45

1982 124.0 (-)16.20 105.0 (-)17.30

1987 135.0 (-)8.80 114.0 (-)10.20

1992 133.0 (-)10.10 114.0 (-)10.20

1996 142.0 (-)4.05 120.0 (-)5.50

1997 133.0 (-)10.10 (-6.30) 113.0 (-)11.0 (-5.80) Further adverse effect

1998 132.0 (-)8.10 (-7.0) 112.0 (-)11.80 (-6.70)