The Ganga Morphology - The Ganga: Water Use in the Indian Subcontinent - page 39

8TH

BANK LINE 1 980

8 TH M E

9 TH M E

SERIES OF SPURS
TAGGED TO 8TH.
MARGINAL EMBKT.

NAVIGATION
LOCK AFFLUX BUND

E. RAILWAY

NATIONAL HIGHWAY - 34

FARAKKA
BARRAGE

FEEDER CANAL

Fig. 5.3 River Ganga upstream of Farakka Barrage

cannot carry the required discharge in the present form and even at lower discharges
causes flood. Otherwise, the channel will try to adjust its capacity by eroding the
bed and the bank, if the materials are of friable nature. In an alluvial stream, the
bed and the banks are normally made of materials which once got deposited during
the change of courses, easing adjustment of their capacity. If the bed goes exces-
sive low, it endangers structures on the bank, energy dissipation devices are affected
and protection works and cut-offs downstream are disturbed, or damaged. Because
of reduced depth of tail-water, the surrounding ground-water table also goes down
which affects irrigation and drinking water supply downstream. However, aggrada-
tions and degradation give certain benefits too. The former raises the ground-water
level which facilitates irrigation, drinking water-supply and navigation while the
latter reduces flood hazard but their ill effects are severer than benefits. In both the
cases erosion of bed and bank at some locations increase owing to reduced bed-
gradient, inviting more concentration of the flowing water. A study of the Ganga's
course revealed that it tends to both aggrade and degrade at many places.
The interference of the Ganga's regime by construction of the Farakka Barrage
gave rise these problems and disadvantages. Changes in the water-level, discharge,
sediment movement, bed-slope etc. caused aggradations and degradation of the bed
and the entire reach from Rajmahal to Farakka in upstream and from Farakka to
quite a distance downstream. Alluvial fans formed on the right side and the deep
channel shifted to the left above the barrage. Bank erosion got worse, forming