Topography

The catchment area of the Ganga falls in four countries, namely India, Nepal, Tibet (China), and Bangladesh. The major part of the geographical area of the Ganga basin lies in India which comprises of three large topographic divisions of Indian subcontinent, namely the Himalayan Young Fold Mountains, the Gangetic Plain, and the Central Indian highlands. The Himalayan Fold Mountains comprises the Himalayan ranges including their foot hills with numerous snow peaks rising above 7000m. Each of these peaks is surrounded by snow fields and glaciers. All the tributaries are characterized by well regulated flows and assured supply of water throughout the year by these glaciers. The Gangetic plains, in which the main stem of Ganga lies, situated between the Himalayas and the Deccan plateau, constitute the most of the sub-basin ideally suited for intensive cultivation. It consists of alluvial formation and is a vast flat depositional surface at an elevation below 300m. The Central highlands lying to the south of the Great Plains consists of mountains, hills and plateaus intersected by valleys and river plains. They are largely covered by forests. Aravali uplands, Bundelkhand upland, Malwa plateau, Vindhyan ranges and Narmada valley lies in this region.

 

The Gangetic plains are mostly divided into three parts, Upper Ganga plains, Middle Ganga plains and Lower Ganga plains. The Upper Ganga plain is the part of the Great Plains lying approximately between the Yamuna in the west covering the parts of Uttarakhand and Uttar Pradesh. The region is delimited in the north by 300m contour which separates it from the Garh - Kum Himalaya west of Sarda while theInternational boundary of Nepal marks the limit towards the east. In the south the
Yamuna demarcates its border with the Bundelkhand. The axis of the topographic trough paradoxically lies nearer the peninsular block or along the Ganga which traverses the area in a south-southeasterly direction. Thus there is, though not perceptible, a tract adjacent to the foot hills where the slope is higher and has resulted in the preponderance of numerous small streams, assigning a somewhat medium to fine texture to this part. The southern counterparts, particularly north of the Ganga are characterized by the sluggishly-flowing streams like the Ramganga and the Ghaghara studded with ox-bows, sandy stretches (the Bhurs) etc. The topographic diversities produced by the changing river courses are predominantly observed in the Ramganga and the Ghaghara valleys, particularly in their flood plains.

 

The streams such as the Kali, the Hindan, and the Pandu etc. have to go a long way parallel to their master streams to empty themselves. Distinct, though areally insignificant, in topographic expressions is the Yamunapar or the Yamuna-lower Chambal tract. The deep valley separated by sharp spurs and buttresses are the main features of Upper Ganga Plain. Topographically most significant and complex part of the region is the submontane belt, running at the foot of the Shiwaliks from west to east across the area on the northern border consisting of the two parallel strips - the piedmont zone, the Bhabar (the Doab region) and the adjoining relatively gently sloping Tarai belt.

 

The Middle Ganga Plain is the largest among the three plains of the Ganga. It covers the Bihar plains and the Eastern Uttar Pradesh lying on the entire side of the Ganga and the Ghaghara within the Himalayan and the peninsular ramparts on the north and the south respectively. Structurally the region is the segment of the great Indo-Ganga trough; however it has some marginal portions of the other two major formations that are Siwaliks in the northern part of the Champaran district and the fringes and the projections of the peninsular block in the south. In general, it is below 100m above the sea level, except that is gradually rises from Domariaganj in Basti up to 130m in the North West and up to 150m in the south in cooperating the projections of the southern uplands; in the east the Kosi plain ranges between 30m in the south to 75m in the extreme north. A more pronounced relief is occasioned when the plain meets the hilly area in the north bearing the stamp of their loosely-set gravelly nature, particularly in the extreme north, where the surface appears to be broken by large rivers like the Ghaghara, the Rapti, the Gandak, the Bagmati, the Kosi etc., which comb the region with their affluents in an intricate pattern.

 

The Lower Ganga Plain includes the Kishanganj district of Bihar, whole of West Bengal excluding the Purulia district and the mountainous parts of Darjeeling district and most of the parts of Bangladesh. The region embraces the area from the foot of the Darjeeling Himalayas in the north to the Bay of Bengal in the south and from the edge of the Chottanagpur Highlands in the west to the border of Bangladesh and Assam in the east. Topographic expressions in the region hardly speak of any well-defined stage of their evolution. The monotonous surface is dissected frequently by the channels of the tributaries or distributaries of the main stream, the Ganga. There are:

 

   The Malda west Dinajpur tract where the inliers of the lateritic alluvium are sufficient to break the general monotony of the plain,

   The tract bordering the Chottanagpur Highlands,

   The Midnapore Coast where the sand dunes on the terraces appear to be more significant element of landforms,

   The Duars of Jalpaigurl and Darjeeling. To the east of the shoreline lies bulge of the Ganga (Sundarbans) where the depositional activity of the stream is prominent and new surface is being continuously added.

 

Many important tributaries of Ganga originate in the Himalayas in India and Nepal; Bangladesh lies in the deltaic region of the basin. The total length of the Ganga River is 2,525 km which makes it the 20th longest river in Asia and the 41st longest in the world (Philips World Atlas). The navigable length of Ganga River is 631 km which mostly lies in Bihar. An index map of the basin is given here.

 

Although the headwaters region of Ganga in the Himalayas is dotted by a number of mighty tributaries, the Bhagirathi River that rises from the Gangotri glacier near Gomukh at an elevation of about 7,010m above mean sea level is traditionally considered to be the source of Ganga River.


The other main stream that originates in the Uttarakhandl state of India is the Alakhnanda. Flowing downhill, Bhagirathi and Alakhnanda are joined by a number of streams, such as the Mandakini, the Dhuli Ganga, and the Pindar. These two rivers (Bhagirathi and Alakhnanda) meet at a place called Devprayag and thereafter the combined flow is known by the name Ganga.

 

Ganga enters into plains near Haridwar and from here it flows in south/southeasterly direction. Yamuna is the most important tributary of the Ganga that joins it on the right bank at Allahabad. After confluence with Yamuna, the Ganga River flows in an eastward direction and is joined by a number of tributaries, such as the Ramganga, the Gomti, the Ghaghra, the Gandak, the Bagmati, the Kosi, the Sone and the Damodar.

 

The delta of Ganga is said to begin at a place known as Farakka where a barrage has been constructed to control river flow. At about 40 km downstream of Farakka, the river splits in two arms. The right arm, the Bhagirathi River, flows towards south and enters the Bay of Bengal about 150 km downstream of Calcutta. The left arm, known as Padma, turns towards east and enters Bangladesh. While flowing in Bangladesh, Padma meets the Brahmaputra River at a place known as Goalundo. The combined flow, still known as Padma, is joined by another mighty river, Meghna, at Chandpur, 105 km downstream of Goalundo. Further down, the river ultimately flows into the Bay of Bengal.

 

The Ganga basin extends over an area of 1,086,000km2. It lies between east longitudes 73 30' to 89 0' and north latitudes 22 30' to 31 30'. The drainage area lying in India is 862,769km2 which is nearly 26.2% of the total geographical area of the country. Some tributaries, such as the Ghagra, the Gandak and the Kosi, drain areas in Nepal amounting to 190,000km2. The delta of the Greater Ganga basin covers an area of 56,700km2. The Ganga basin is bounded on the north by the Himalayas, on the west by the Aravalis and the ridge separating it from the Indus basin, on the south by the Vindhyas and Chhotanagpur plateaus and on the east by the Brahmaputra ridge. The basin lies in the States of Uttarakhand, Uttar Pradesh, Madhya Pradesh, Bihar, Rajasthan, West Bengal, Haryana, Himachal Pradesh and the Union Territory of Delhi. The State-wise distribution of the drainage area is given in Himalayas, on the west by the Aravalis and the ridge separating it from the Indus basin, on the south by the Vindhyas and Chhotanagpur plateaus and on the east by the Brahmaputra ridge. The basin lies in the States of Uttaranchal, Uttar Pradesh, Madhya Pradesh, Bihar, Rajasthan, West Bengal, Haryana, Himachal Pradesh and the Union Territory of Delhi. The State-wise distribution of the drainage area is given in below:

State-wise distribution of the drainage area of Ganga River in India

State

Drainage area (km2)

 Uttarakhand and Uttar Pradesh

294,410

 Madhya Pradesh

199,385

 Bihar

143,803

 Rajasthan

112,490

 West Bengal

72,618

 Haryana

34,271

 Himachal Pradesh

4,312

 U.T. of Delhi

1,480

Total

862,769

 

From a hydrological studies point of view, the entire run of Ganga River in India can be divided in three stretches or reaches. The upper reach extends from the origin to Narora, the middle reach from Narora to Ballia, and the lower reach from Ballia to its delta. The main physical sub-divisions of the Ganga basin are the Northern Mountains, the Gangetic Plains and the Central Highlands. Northern Mountains comprise the Himalayan ranges including their foothills. The Gangetic plains, situated between the Himalayas and the Deccan plateau, constitute the most fertile plains of the basin that are ideally suited for intensive cultivation. The central highlands lying to the south of the Great Plains consists of mountains, hills and plateaus intersected by valleys and river plains. They are largely covered by forests. Aravalli uplands, Bundelkhand upland, Malwa plateau, Vindhyan ranges and Narmada valley lie in this region.

 

The terrain of the basin is very rugged in the north-eastern part and flat towards downstream side. The Himalayan region of the basin contains nine of the fourteen highest peaks in the world over 8,000m in height, including Mount Everest which is the highest point of the basin. The other peaks over 8,000m in the basin are Kangchenjunga, Lhotse, Makalu, Cho Oyu, Dhaulagiri, Manaslu, Annapurna and Shishapangma. The Himalayan portion of the basin includes the southeastern portion of the state of Himachal Pradesh, the entire state of Uttarakhand and the extreme north-western portion of the state of West Bengal. Major area of the basin falls within 300-500 m elevation zone. The elevation variation the basin is given below :

 

Elevation zones

Sl. no.

Elevation (m)

Area (Sq.km.)

% of Total Area

1

< 5

10441.16

1.21

2

5-10

8320.58

0.97

3

10-50

58940.57

6.84

4

50-100

122902.46

14.27

5

100-200

200790.42

23.31

6

200-300

123124.65

14.29

7

300-400

105002.90

12.19

8

400-500

114920.62

13.34

9

500-750

59722.04

6.93

10

750-1000

8741.36

1.01

11

1000-1500

11636.73

1.35

12

1500-2000

10699.95

1.24

13

2000-3000

9540.63

1.11

14

3000-4000

4886.73

0.57

15

4000-5000

6320.05

0.73

16

5000-6000

5096.32

0.59

17

> 6000

364.8297

0.042351

 (Source: India_WRIS)