What Went Wrong? - The Ganga: Water Use in the Indian Subcontinent - page 220

cusecs, but these do not tally with the figures of prototype observations in several
years. In some critical years, if the flow falls to about 45,000 cusecs, minimum
35,000 cusecs are to be released to one side, as per the Treaty, the other side gets
only 10,000 cusecs, bringing down the discharge, instantly, by 25,000 cusecs from
one 10-day period to the next. Even if the average flow is around 50,000 cusecs,
a guaranteed discharge of 35,000 cusecs would flow to one side and only 15,000
cusecs to the other side, reducing the total flow by 20,000 cusecs in the next 10-day
period. This abrupt fall will severely affect the canal-bed and the banks owing to
sudden fall in external water-pressure, of the tractive force of flowing water and
cause bank-slips, silt deposits on the bed, rendering the canal cross-section unsta-
ble. However, the Ganga being more wide than deep, the vertical difference owing
to such falls in discharge would not be much and bank-slips would not be severe.
As the canal is much narrower than the Ganga, vertical fluctuations would be appre-
ciable and bank-slips and slides would be more severe. This occurred in 1997 and
affected the banks of the canal in about 30 places, following big and small slips in
March and April. Sharing of the Ganga water from 1977, as per the Treaty, actu-
ally increased siltation in the river-bed. The envisaged benefits did not accrue to
the extent desired. The Bhagirathi-Hooghly did not receive 40,000 cusecs, round
the year, from 1978. In the lean seasonpreviously, flow-tides carried huge silt-load
which could only be reduced by maximum upland discharge. After 1977, water
became almost silt-free and its scouring capacity reached the maximum. Tides were
quite high in the lean season and a steady flow of 40,000 cusecs, round the year
for at least five years, could degrade the river-bed gradually, to the desired extent.
Expected benefits of Calcutta Port after the commissioning of the barrage included
up and down movement of vessels of 7.93 m, or 26 feet, draught, round the year,
of 8.54 m or 28 feet draught for 200 days and of 8.84 m, or 29 feet, for 100 days,
but this was not achieved. Only vessels of 6.71 m or 22 feet draught, plied round
the year until 1996; vessels of 8.54 m could not come to the port, even for a single
day. The salinity of water, supplied to Kolkata and Howrah regions also, was not
reduced, to the desired extent. Thus, although the barrage brought some benefits
to the port, they were far less than those envisaged before the construction of the
barrage.
The discharges in the lean season being much less than required, navigation
did not improve much and chars emerged, particularly below Diamond Harbour.
Navigation on the Haldia channel was blocked by silt and loaded ships could not ply
through the Haldia channel now. The ships now pass through the Rangafalla chan-
nel, near Kulpi. The bores during flood-tides in Kolkata region continue to occur but
less frequently than before the barrage, in about 50 days as against 120 days before.
Unstable flows caused erosion of banks and left a huge volume of silt on the bed,
making it unstable too. It has to be admitted, however, that although some envisaged
benefits eluded, some were indeed achieved.
After the signing of the 1996 Treaty, siltation, salinity, bore tides, bank erosion
etc. increased because of fluctuations in flows - 10 days less and 10 days more - in
the lean season, the water current also varied. The silt-load that, entering the river,
moves upward with flow-tide and is deposited in the bed cannot be wholly scoured.