The country's rivers are classified as Himalayan, peninsular, coastal, and inland-drainage basin rivers. Himalayan rivers are snow fed and maintain a high to medium rate of flow throughout the year. The heavy annual average rainfall levels in the Himalayan catchment areas further add to their rates of flow. During the monsoon months of June to September, the catchment areas are prone to flooding. The volume of the rain-fed peninsular rivers also increases. Coastal streams, especially in the west, are short and episodic. Rivers of the inland system, centered in western Rajasthan state, are few and frequently disappear in years of scant rainfall. The majority of the South Asia's major rivers flow through broad, shallow valleys and drain into the Bay of Bengal.

The Ganga River basin, India's largest, includes approximately 25 percent of the nation's area; it is bounded by the Himalayas in the north and the Vindhya Range to the south. The Ganga has its source in the glaciers of the Greater Himalayas, which form the frontier between India and Tibet in northwestern Uttar Pradesh. Many Indians believe that the legendary source of the Ganga, and several other important Asian rivers, lies in the sacred Mapam Yumco Lake (known to the Indians as Manasarowar Lake) of western Tibet located approximately 75 kilometers northeast of the India-China-Nepal tripoint. In the northern part of the Ganga River basin, practically all of the tributaries of the Ganga are perennial streams. However, in the southern part, located in the states of Rajasthan and Madhya Pradesh, many of the tributaries are not perennial.

The Brahmaputra has the greatest volume of water of all the rivers in India because of heavy annual rainfall levels in its catchment basin. At Dibrugarh the annual rainfall averages 2,800 millimeters, and at Shillong it averages 2,430 millimeters. Rising in Tibet, the Brahmaputra flows south into Arunachal Pradesh after breaking through the Great Himalayan Range and dropping rapidly in elevation. It continues to fall through gorges impassable by man in Arunachal Pradesh until finally entering the Assam Valley where it meanders westward on its way to joining the Ganga in Bangladesh.

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

The source of the Godavari is northeast of Bombay (Mumbai in the local Marathi language) in the state of Maharashtra, and the river follows a southeasterly course for 1,400 kilometers to its mouth on the Andhra Pradesh coast. The Godavari River basin area is second in size only to the 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 its discharge, despite the large catchment area, is moderate because of the medium levels of annual rainfall, for example, about 700 millimeters at Nasik and 1,000 millimeters at Nizamabad.

The Krishna rises in the Western Ghats and flows east into the Bay of Bengal. It has a poor flow because of low levels of rainfall in its catchment area--660 millimeters annually at Pune. Despite its low discharge, the Krishna is the third longest river in India.

The source of the Kaveri is in the state of Karnataka, and the river flows southeastward. The waters of the river have been a source of irrigation since antiquity; in the early 1990s, an estimated 95 percent of the Kaveri was diverted for agricultural use before emptying into the Bay of Bengal. The delta of the Kaveri is so mature that the main river has almost lost its link with the sea, as the Kollidam, the distributary of the Kaveri, bears most of the flow.

The Narmada and the Tapti are the only major rivers that flow 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). The shorter Tapti follows a generally parallel course, between eighty kilometers 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.

Harnessing the waters of the major rivers that flow from the Himalayas is an issue of great concern in Nepal, India, and Bangladesh. Issues of flood control, drought prevention, hydroelectric power generation, job creation, and environmental quality--but also traditional lifestyles and cultural continuities--are at stake as these countries grapple with the political realities, both domestic and international, of altering the flow of the Ganga and Brahmaputra. Although India, Nepal, and Bangladesh seek to alleviate problems through cooperation over Himalayan rivers, irrigation projects altering the flow of Punjab-area rivers are likely to continue to be an irritant between India and Pakistan--countries between which cooperation is less likely to occur--in the second half of the 1990s. Internally, large dam projects, such as one on the Narmada River, are also controversial.