The Geography of the Ganges: River Systems and Urban Development?

The Ganges flows 1,560 kilometres from its source in the Himalayan glaciers of Uttarakhand to the Bengal delta, draining a basin of 1.06 million square kilometres. It is the lifeblood of northern India: the water that irrigates the rice and wheat of the Indo-Gangetic plain, fills the wells of villages across the Doab, and supplies drinking water to the cities that line its banks from Rishikesh to the Bay of Bengal. Roughly half a billion people depend on it directly.

The river's distribution is unequal and becoming more so. The monsoon brings the bulk of the annual discharge—roughly 71,000 cubic metres per second in a normal year—between June and September. By March, before the rains return, flow in the middle reaches can drop below 1,000 cubic metres per second. The dry-season discharge at Allahabad has fallen from a historical average of 3,200 cubic metres per second in the early twentieth century to roughly 2,100 cubic metres per second by 2000, a decline attributed to both dam construction upstream and to glacial retreat in the high mountains. The All-India Institute of Hydrological Research estimates that Himalayan snowmelt now contributes only 30 percent of summer flow, down from roughly 50 percent a century ago.

Irrigation claims the largest share of the Ganges waters. The Upper Bari Doab Canal system, completed in stages between 1858 and 1975, draws water near the Sutlej confluence. The Ganges Canal, built between 1842 and 1854, serves more than 5 million hectares of wheat and sugarcane across Uttar Pradesh. The Indira Gandhi Canal, extended into Rajasthan after 1975, carries water hundreds of kilometres from the Sutlej, not the Ganges proper, but competes for the same dry-season flow. In total, irrigation consumes an estimated 64 percent of the Ganges basin's available discharge. Industrial demand accounts for another 8 percent, and urban and domestic consumption for roughly 6 percent. The remaining 22 percent reaches the delta during the dry season and flows into the Bay of Bengal.

Urban water demand has grown faster than the cities that depend on it. Kolkata, the largest city in the delta, draws roughly 1,200 million litres per day from the Hooghly—the main eastern distributary of the Ganges—to supply a metropolitan population of roughly 15 million. The Calcutta Metropolitan Development Authority's water supply plan of 1998 projected that demand would reach 2,050 million litres per day by 2020. In Varanasi, one of Hinduism's holiest cities, domestic consumption rose from 34 million litres per day in 1990 to 84 million litres per day by 2015, even as the dry-season flow of the river fell by roughly a third. The competition between riparian cities has produced bitter disputes: upstream users—Delhi, Mathura, the textile mills of Kanpur—deplete the river before it reaches downstream cities, and the delta cities pay the cost in salinity and scarcity.

The quality of the water has become as urgent as its quantity. Industrial effluent from tanneries and petrochemical plants, untreated municipal sewage, and agricultural runoff rich in nitrates and phosphates have reduced the Ganges to a biological desert across much of its middle reach. The Central Pollution Control Board reported in 2005 that stretches of the river in Uttar Pradesh carried biochemical oxygen demand levels ten times higher than drinking water standards. Many cities have no treatment capacity: in Kanpur, whose 2.7 million people discharge roughly 250 million litres of untreated municipal sewage daily into the river, the water is dark brown from mid-April through May.

The Ganges Action Plan, launched in 1986 and extended four times since, has built treatment plants and restored embankments in major cities, at a cost of roughly 200 billion rupees spread across thirty years. Yet water quality below major urban centres has continued to degrade. Scholars disagree on whether the causes are mainly urban and industrial, or whether agricultural runoff now constitutes the larger burden. The Ministry of Environment and Forests published estimates in 2006 suggesting that agricultural chemicals account for 52 percent of the biological load entering the river; the Indian Institute of Technology at Kanpur contends the figure is closer to 38 percent and attributes the difference to measurement bias in rural collection points.

The delta itself faces an existential threat from the same dry-season decline that pinches the cities upstream. The Sundarbans mangrove forests, which once covered 16,000 square kilometres, have shrunk to roughly 9,600 square kilometres, partly from agricultural clearing but substantially from saltwater intrusion as freshwater flow from the Ganges has diminished. A study by the West Bengal Directorate of Forests estimated in 2008 that the remaining forest had contracted by 102 square kilometres in the previous decade. Loss of the Sundarbans has meant loss of habitat for the Bengal tiger, whose population in the delta fell from roughly 3,000 individuals in 1980 to 68 animals by the 2004 census. Cities and agriculture have together wrung the delta dry, and the consequences are now visible in the extinction of species and the submergence of islands.

Climate projections for the basin expect the monsoon onset to become less predictable and the dry season more severe. The hydrological regime that sustained Indian civilization for millennia is altering on a timescale of decades, and the institutions that manage the river—built for the climate of the twentieth century—have not yet adapted to it.