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. 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 valley in Uttarakhand State is a place of breath taking natural beauty. It is the home of the world renowned Valley of Flowers, a protected area. The famous high altitude Nanda Devi Biosphere Reserve is now a part of the Unesco’s Global Network of World Heritage sites. This reserve will be soon included in the Man and Biosphere program to assess the global changes in biosphere reserves in mountains.
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
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 :