The Ganga’s Hydrology - The Ganga: Water Use in the Indian Subcontinent - page 32

Table 4.9 Average bed slope of the river Ganga

Stretch Section Length (Km) Average bed slope

1 2 3 4

Source to Rishikesh Mountainous 355 1 in 67

Rishikesh to Allahabad Upper Plain 800 1 in 3,196

Allahabad to Farakka Middle Plain 960 1 in 15,795

Farakka to Nabadwip Deltaic nontidal Plain 230 1 in 23,000

Nabadwip to Outfall Deltaic tidal Plain 310 1 in 24,000

The gigantic Brahmaputra-Yamuna joins the Ganga further down in Pabna dis-
trict of Bangladesh; both in length and breadth, the combined river is one of the
largest in the world. In rainy season, the width is nowhere less than 3 km; in some
places, it even exceeds 6 km. The average rainy season discharge often exceeds
42,476 cumecs, i.e., 1.5 million cusecs, and the peak discharge in some years
was over 70,793 cumecs, or 2.5 million cusecs. In discharge, it ranks with the
world's seven largest rivers - the Amazon, the Congo, the La Plata, the Yangtze,
the Mississippi and the Ganga, The total length of the Tsang po-Brahmaputra-
Yamuna is about 2,900 km, draining a total area of about 573,000 km 2 .Ofthis,
about 289,000 km 2 area is in Tibet, 238,000 km 2 area is in India and 46,000 km 2
area is in Bangladesh. The drainage area, north of Bahadurabad and Bangladesh
is about 530,000 km 2 . The highest recorded peak discharge was 71,331 cumecs
(2,519,000 cusecs) at Bahadurabad.
Further down, the Meghna joins the Ganga-Brahmaputra and the combined chan-
nel flows into the Bay of Bengal as Meghna. It alone has a peak discharge of about
12,200 cumecs and average of about 7,000 cumecs. It originates in the Barak Valley
in Assam and enters Bangladesh near Sylhet town. The confluence of the Ganga-
Brahmaputra-Meghna is more than 11 km wide in rainy months, making it again
one of the largest rivers of the world.
Thus Bangladesh receives a vast quantity of water, round the year, from the three
separate streams, estimated at 1.096 million cubic metre on an average in a year. If
the total rainfall, estimated at 0.25 million cubic metre is added, a mind-boggling
1.346 million cubic metre of water flow through Bangladesh. A part of this huge
water percolates under ground but the rest flows to the sea. This vast flow is second
only to that of the Amazon and the total yearly volume of flow of the Padma-Meghna
makes it the second largest river in the world. However, owing to large seasonal
fluctuations in the flow, correlating with the quantum of rainfall in the Himalayan
region in India, Nepal and Bhutan, the flow in August is almost seven times of that
in February. The average monthly flow in these three rivers through Bangladesh is
shown in Table 4.10.
It may be noted that the Brahmaputra gains the discharge from April, whereas
the Ganga gains it from July, i.e., nearly 3 months afterward, each year. Moreover,
high discharge prevails in the Brahmaputra for about seven months, from April to
October but peaking in July and August. In the Ganga, high discharge obtains for