The Ganga Morphology - The Ganga: Water Use in the Indian Subcontinent - page 42

M A L D A

C H A R
L A N D

C H A R
L A N D

G A N G A

AURANGABAD

DHULIAN

BENIAGRAM

NAVIGATION
LOCK

M U R S H I D A B A D

Fig. 5.5 River Ganga downstream of Farakka

very irregular; it used to be quite high in August and September but nominal, or nil,
during rest of the year.
The Hooghly's flow is oscillating; the water-level fluctuates twice a day, owing
to the tides and changes its hydro-morphology. Its estuary below Diamond Harbour
being funnel-shaped, it restricts the optimum tidal influx which primarily governs
the channel regime and its navigability. Before induction of the upland discharge
from Farakka, the flow pushed the sand further up and made the river shallower. The
induction of upland flow has reduced the sand movement considerably, degrading
the river-bed.
In the pre-Farakka era, before the induction of upland discharge, the Bhagirathi-
Hooghly reached a moribund state in its upper reach and a mature state in the middle
reach from Nabadweep to Kolkata. However, the lower reach, south of Kolkata,
remained active under tidal influence. Its cubic capacity decreased owing to depo-
sition of silt and sand at the mouth and bed. After a barrage came up at Farakka, a
discharge of 1,132 cumecs, or 40,000 cusecs, flows into the river in most part of the
year, restrictions are imposed for the dry season, i.e., from January to May, when the
discharge through the Feeder Canal reduced considerably, substantially improving
the overall performance of the river. The bed started degrading and channel param-
eters, like width, hydraulic mean depth, cross-sectional area and the cubic capacity
of the river increased. The moribund stage of the pre-Farakka condition gave way to
the active stage in post-Farakka period.
An analysis of the channel pattern shows numerous meander stretches, sepa-
rated by braids and also straight reaches at some places. There are four prominent
braided reaches in the entire 450 km course of the river from Jangipur to Diamond
Harbour, namely, the outfall to Raghunathpur (3 km), Chowrigachha to Suti (3 km),
Katwa to Baladanga (12 km) and Zirat to Bansberia (3 km) - all north of Kolkata. In
three braided reaches, the course is divided by the point-bars in mid-stream. There
are many channels in Katwa-Baladanga reach where point-bars are intercepted by
cross-channels. The river has a number of apparently straight reaches, uniting either