Geoscience Reference
In-Depth Information
Nepal as well as from the Indian soil on the south of Himalayan foothills. The major
tributaries from the north are the Rama Ganga which joins the Ganga much above
the confluence with the Yamuna at Allahabad, the Gomati, the Ghagra with its three
tributaries - the Sarda, the Karnali and the Rapti, the Gandak and the Kosi with its
two tributaries - the Buri Gandak and the Bagmati, the Kamala, the Sun Kosi and
the Arun Kosi. The Gomati flows entirely within the Indian territory; the Sarda flows
in India except a small portion in Nepal, the Karnali, the Rapti, the Gandak and the
Kosi and their tributaries originate in Nepal. On the south, Yamuna joins the Ganga
at Allahabad where its total annual run-off is more than that of the Ganga. The aver-
age annual run-off of the Ganga is about 0.06 trillion (10
12
) cubic metre against
0.09 trillion (10
12
) cubic metre for the Yamuna. Thus, the combined run-off of the
Ganga below the confluence is about 0.15 trillion (10
12
) cubic metre. With the con-
tribution from the tributaries on both sides the average annual run-off of the Ganga
at Farakka increases to about 0.4 trillion (10
12
) cubic metre, owing to contribution of
the tributaries from both sides. Out of this total run-off, the contribution from Nepal
is approximately 20% only, which flow through tributaries originating in Nepal.
As stated, the catchment area of the Ganga basin between the Himalayan (north-
ern side) and the peninsular sub-basins (southern side) is in the ratio of about
60:40, but the discharge contribution is just the reverse, i.e., about 40:60 owing
to more intense rainfall in the Himalayan range and also over the foothills than
that of the peninsular region. Thus, hydrologically, the Himalayan rivers contribute
more to the management of water resources than the peninsular streams. Of the
Himalayan streams, the Ghagra with its tributaries contribute maximum run-off -
about 94,500 Mm
3
and the Gomati up to about 7,400 Mm
3
cusecs. Of the penin-
sular streams, the Sone contributes run-off up to 32,000 Mm
3
and the Kosi gives at
least 5,000 Mm
3
run-off. The Yamuna is not a peninsular stream, as it originates in
the Himalayan range, not far from the origin of the Ganga. The details of catchment
area of the tributaries are shown in Table 14.1 below.
Average annual run-off of the Ganges at Farakka varies from 0.35 to 0.40 trillion
(10
12
) cubic metre.
Above the confluence with Yamuna at Allahabad-
Run-off of the Ganges — 0.053 trillion (10
12
)m
3
— 13%
Run-off of the Yamuna — 0.098 trillion (10
12
)m
3
— 25%
Total — 0.151 trillion (10
12
)m
3
— 38%
Therefore, the average annual run-off between Allahabad and Farakka is (0.40 -
0.151) 0.249 trillion (10
12
)m
3
.
Now, contribution from Northern side is about 60% and that from Southern side
is 40%.
Therefore, contribution from Northern side is 0.149 trillion (10
12
)m
3
.
Say, 0.150 trillion (10
12
)m
3
.
Considering 50% run-off from Nepal, contribution from Nepal is 0.075 trillion
(10
12
)m
3
. This is about 19%, or say, 20% of the annual run-off available at Farakka,
or about one-fifth of the average annual run-off at Farakka. A schematic diagram of
the Ganges river with its tributaries on either side and of other rivers of India and
the neighbouring countries is shown in Fig. 14.1.
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