Based on the topography, the river systems of India can be classified into four groups. These are:

        Himalayan Rivers    Deccan Rivers    Coastal Rivers     Rivers of the Inland Drainage Basin

The Himalayan Rivers

The Himalayan Rivers receive input from rain as well as snowmelt and glacier melt and, therefore, have continuous flow throughout the year. During the monsoon months of June to September, Himalayas receive very heavy rainfall and experience maximum snow melt and these are the periods when the rivers carry about 80% or more of the annual flows. This is also the time when these rivers are prone to flooding.

The main river systems in Himalayas are those of the Indus and the Ganga-Brahmaputra-Meghna. The Indus rises near Mansarovar in Tibet. Flowing through Kashmir, it enters Pakistan and finally falls in the Arabian Sea near Karachi. A number of important tributaries of Indus flow through India, namely, the Sutlej, the Beas, the Ravi, the Chenab and the Jhelum.

Bhagirathi and Alakhnanda are two important rivers that originate in Garhwal Himalayas. These join at Devprayag to form Ganga which is the most sacred river of India. This river traverses through Uttaranchal, Uttar Pradesh, Bihar, and West Bengal and thereafter enters Bangladesh. The important tributaries of Ganga are the Yamuna, the Ramganga, the Ghaghra, the Gandak, the Kosi, and the Sone. Many of these tributaries are mighty rivers themselves. Yamuna River is an important tributary of Ganga and its own important tributaries are Chambal and Betwa.

The Brahmaputra rises in Tibet where it is known by the name Tsangpo. It enters India in Arunachal Pradesh and after traversing through Assam, enters Bangladesh. Its important tributaries are the Dibang, Lohit, Subansiri, Manas and Teesta. Ganga and Brahmaputra rivers meet at Goalundo in Bangladesh. The Barak River, the head stream of Meghna rises in the hills in Manipur. The Meghna is the part of Ganga-Brahmaputra-Meghna-System. The combined Ganga-Brahmaputra River meets Meghna in Bangladesh and their huge volume of water flows into the Bay of Bengal.

Harnessing the waters of the major rivers that flow from the Himalayas is of paramount importance for India, Nepal, and Bangladesh. Through a close collaboration and pooling resources, huge benefits can be realized from flood control, assured irrigation, hydroelectric power generation, employment generation, and improvement of environmental quality. As these countries grapple with the political compulsions and realities, both domestic and international, of utilizing the flow of the Ganga-Brahmaputra system, precious water, largely unutilized, continues to flow to the sea. At times, it also inflicts large losses to life and property.

 Principal Himalayan rivers of India

The Deccan Rivers

The rivers of Deccan can be further classified in two groups: west flowing rivers and east flowing rivers. The Narmada and the Tapi rivers flow westwards into Arabian Sea. The important east flowing rivers are the Brahmani, the Mahanadi, the Godavari, the Krishna, the Pennar, and the Cauvery. These rivers fall into the Bay of Bengal.

The Mahanadi, rising in the state of Madhya Pradesh, is an important river in the state of Orissa. In the upper drainage basin of Mahanadi, which is centered on the Chhattisgarh Plain, periodic droughts contrast with the situation in the delta region where floods damage the crops in the rice bowl of Orissa. Hirakud Dam, constructed in the middle reaches of Mahanadi, has helped in alleviating these adverse effects to a large extent by creating a reservoir.

The source of the Godavari is near Nasik, northeast of Mumbai (Bombay) in the state of Maharashtra, and the river follows a southeasterly course for 1,400 kilometers (km) to its mouth on the Andhra Pradesh coast. The Godavari basin is second in size only to Ganga; its delta on the east coast is also one of the country's main rice-growing areas. It is known as the Ganga of the South but despite the large catchment area, its discharge is moderate. The reason is medium depth of annual rainfall, for example, about 700 mm at Nasik and 1,000 mm at Nizamabad.

The Krishna rises in the Western Ghats and flows east into the Bay of Bengal. Its flow is not very large because of low rainfall in its catchment area: 660 mm annually at Pune. The Krishna is the third longest river in India.

The source of the Cauvery is in the state of Karnataka and the river flows southeastward. Its main tributaries are the Bhima, the Tungabhadra, the Ghatprabha and the Malaprabha. The waters of the river have been a source of irrigation since antiquity; in the early 1990s, an estimated 95% of the Cauvery flow was diverted for agricultural use.

The Narmada and the Tapi are the only major rivers that flow eastward into the Arabian Sea. The Narmada rises in Madhya Pradesh and crosses the state, passing swiftly through a narrow valley between the Vindhya Range and spurs of the Satpura Range. It flows into the Gulf of Khambhat (or Cambay). Tapi which is of shorter length follows a generally parallel course, between 80 km and 160 kilometers to the south of the Narmada, flowing through the states of Maharashtra and Gujarat on its way into the Gulf of Khambhat.

The Coastal Rivers

There are numerous coastal rivers which are comparatively small. While only handful of such rivers drain into the sea near the deltas of east coast, there are as many as 600 such rivers on the west coast. The West Coast rivers are important as they contain as much as 14% of the country’s water resources while draining only 3% of the land.

Rivers of the Inland Drainage Basin

The rivers of the inland system, centered in western Rajasthan state, are few and frequently disappear in years of scant rainfall. A few rivers in Rajasthan do not drain into the sea. They drain into salt lakes or get lost in sands with no outlet to sea.