Ganges River

The Ganges River flows from the Himalayas through the northern and eastern portions of India, continuing through Bangladesh to the Bay of Bengal. Although the Ganges is not a long river, it is the second-muddiest river in the world, depositing sediment along the fertile floodplains and at the delta. The Ganges system annually floods and periodically causes great loss of life and damage.

History

The Ganga River is known in the Western world by its anglicized name of the Ganges River. The Ganges River has been one of the most important Asian rivers in recorded human history. Indian civilizations dating back to the kingdom of Ashoka in the third century BCE developed along the Ganges River or in the floodplains of the Indo-Gangetic Plain. Today, millions of people in India and Bangladesh rely on its waters. The population of the Indo-Gangetic Plain is over 800 million people, making it one of the most heavily populated river basins in the world.

The Ganges River is the holiest of rivers for Hindus, and its creation is featured in mythology. Many devout Hindus travel long distances to bathe in its waters at Varanasi, which is India's oldest city. This ritual is considered an act of purification, and for many, is the culmination of one’s life. Hindus also believe that dying and having one’s ashes scattered on the Ganges will ensure moksha, or the release from the constant cycle of death and reincarnation. Because of these beliefs, there are numerous crematoria along the Ganges at Varanasi, and many ashes and bodies are given over to the river each year.

Geography of the Ganges

The Ganges River arises from the runoff from the southern side of the Himalayas, the world’s highest mountain range. The Ganges River flows about 2,500 kilometers across the Indo-Gangetic Plain and through a coastal delta in Bangladesh to empty into the Bay of Bengal. The river system drains a basin totaling more than 580,000 square kilometers, nearly one-fourth of the area of India. The average discharge of the Ganges is about 11,610 cubic meters per second, but floods from upland rains and snowmelt can increase the discharge by a factor of five or more.

Many believe that the source of the river is an ice cave at the base of a glacier at Gangatri, from which the Bhagairathi River flows. The true source of the Ganges is, however, considered to be some 21 kilometers to the southeast at Gaumukh. After flowing southward off the southern face of the Himalayas, the Ganges River flows predominantly eastward along the front of the Himalayan system, later turning southward as it makes its final way to the sea. The headwaters of the Ganges consist of five rivers that all arise in the northern Indian state of Uttarakhand. The main tributaries are the Bhagirathi, Alaknanda, Mandakini, Dhauliganga, and Pindar Rivers. The Bhagirathi and the Alaknanda Rivers merge at Devprayag to form the main stream of the Ganges River. The Ganges then cuts its way through the southern outer mountains of the Himalayas and emerges from the mountains at Rishikesh. From Rishikesh, the Ganges flows out onto the Gangetic Plain at Haridwar and continues eastward, still within the state of Uttarakhand. From this area eastward, the Ganges River is joined by the Yamuna River—which flows past the capital city of New Delhi—as well as the Tons, Ramganga, Gomati, and Ghaghara Rivers. The Ganges River then flows eastward into the Indian state of Bihar, where it is joined by the Gandak, Buhri Gandak, Ghugri, and Kosi Rivers, all of which arose in the mountains to the north.

These rivers provide more than 40 percent of the entire flow of the Ganges River. The surface waters of the area south of the Ganges are drained into the main river primarily by the Son River. After flowing northward around the Rajmahal Hills, the Ganges River turns southward and flows into the state of West Bengal. The river here is generally known as the Padma River and enters the delta region at Farakka. To the south, the Ganges River and the great Brahmaputra River merge and flow southward into the Bay of Bengal. Many tributaries and many distributaries carry the water across the wide delta in Bangladesh.

Hydrology

The hydrologic regime in the Ganges River system is highly seasonal, with up to 80 percent of the rainfall occurring in the interval from July through October. This heavy rainfall is caused by the southwesterly monsoons that cross the region during this time. Significant quantities of water are also added by melting snow in the Himalayas during the spring months. Rainfall, however, varies considerably over the entire river basin. In the western part of the basin, precipitation averages about 750 millimeters per year, but up to three times that much falls in the eastern part of the basin. In addition to the annual rainfall and snowmelt, water is added to the rivers by the base flow of the groundwater systems that are contiguous with the river.

The strong seasonal nature of precipitation is shown in the variations in the discharge of the Ganges system throughout the year. Discharge at the Hardinge Bridge in Bangladesh averages 39,400 cubic meters per second in August but may rise to a maximum of more than 53,000 cubic meters during flood stage. In contrast, the mean discharge at the same location during the height of the dry season from February through May is only slightly more than 21,000 cubic meters. Most of the flow during the dry season is derived from the northern tributaries of the Ganges River.

In addition, the delta region is commonly buffeted by severe cyclonic storms that generally just precede the onset of the monsoon season or occur at the end of the main rainy season. These storms have been responsible for many of the damaging and deadly floods in the delta region.

Sedimentation

The rivers that flow out of the highlands of the southern Himalayas generally have high velocity and, therefore, a very high competency. The land in many areas is highly erodible, particularly if it has been recently deforested. As a result, the rivers carry large amounts of sediment in suspension and as bed load. Based upon suspended load calculations, the Ganges River is variously ranked either first (especially when including the flow of the Brahmaputra system as well) or second behind only the Yellow River in China in terms of sediment load. The average suspended load is about 1.4 billion metric tons per year. This leads to an average of approximately 1,500 metric tons of suspended sediment per square kilometer of the river basin.

The gentle gradient of the Ganges River after it leaves the Himalayas results in relatively little erosion and a low production of suspended load. In contrast, the Kosi River, a northern tributary to the Ganges, has an annual suspended load of only 172 million metric tons per year. However, because of its high gradient and relatively small drainage basin, the average sediment load per square kilometer of basin is almost twice that of the Ganges River as a whole. The high sediment load, coupled with large-scale flooding caused by rapid runoff from the Himalayas, has led to the frequent avulsion of the Kosi River. Its channel shifted more than 100 kilometers in the years between 1736 and 1964.

The gradient of the river across the Indo-Gangetic Plain (south of the Himalayas to the delta) is very shallow. The 1,600-kilometer stretch of river from the Yamuna River at New Delhi to the Bay of Bengal drops only about 1,100 meters in elevation. This shallow gradient leads to low water velocity and rapid deposition of sediment in the river channel and in the floodplains during flood stage. The combination of rapidly rising, very high mountains as a sediment source and a slowly moving major river leads to rapid aggradation of the floodplain surfaces along the river. The Indo-Gangetic Plain is composed of this rapidly deposited sediment and is, in some places, up to 2,000 meters thick. Although the age of the bottom sediments in the basin is not definitely known, it is probable that the deposition of this thick accumulation of sediments was rapid, perhaps occurring within the last 10,000 years.

Sediment that is transported to the coastal area by the Ganges and Brahmaputra Rivers is deposited in the deltaic area. The delta built by these two great rivers is huge, totaling almost 60,000 square kilometers. Like most deltas, this landmass has been built up by the deposition of silts and sands along the main channel and in the many distributaries that channel water to the ocean. The areas between the channels are often heavily vegetated, which leads to the formation of peat when the plants die and are buried in the swampy areas. In some places, the peat has been mined and used as an energy source. The sediments that compose the delta include sand, silt, peat, and marl.

Because of the heavy sediment load and the seasonally variable discharge of the river system, the delta has grown larger and extended farther seaward throughout historic times. New land areas, called khadar, are generally formed in the areas near the present-day channels where the river water meets the oceanic waters. As sediment accumulates, it blocks water flow and forces the river to change its course. In this way, the sediment depositions continually change location, and the delta continues to prograde out into the Bay of Bengal. The current flow pattern of the river is toward the eastern side of the delta in Bangladesh, causing the buildup of land areas and some offshore islands. The western side of the delta has remained essentially unchanged since the eighteenth century. The delta will continue to grow as long as water and sediment are transported by the river to the coast. However, with increasing population growth and the resultant increase in agricultural and urban use of water, the total flow of the Ganges and Brahmaputra Rivers may be significantly reduced. This reduction will lead to the eventual erosion of the coastal delta if the sediment load is not sufficient to compensate for erosive mass wasting.

The seaward edge of the delta is characterized by a vast area of tidal forests and swamps that harbors an immense biological diversity. The tidal forests, known as the Sundarbans, have been declared protected areas by the governments of both India and Bangladesh, which have instituted conservation measures to preserve the biota, including the Bengal tiger.

Floods

As in most areas, flooding has had both beneficial and detrimental effects on the land and the people in the floodplain of the Ganges River. The floods bring down sediment and nutrients into the lower reaches of the river and are responsible for building a fertile floodplain. Records from the sixteenth and seventeenth centuries indicate that the Ganges basin was once heavily forested and was home to a wide variety of animals and plants that are no longer found in the area. Deforestation of the area led to the loss of animal life, and the floodplain today sustains a high level of agricultural productivity. The rapid increase in human population in the region has also led to increasing residential use of the floodplain and, therefore, a growing flood risk for the region. Indeed, in 2023 India became the most populous country in the world, rising above China, and hundreds of millions have settled in the path of flooding along the Ganges.

Even though the area of the state of Bihar near the Ganges is swampy land, the population has grown in that region. Settlement in the floodplain has led to extensive loss of life and property damage during the frequent flooding of the area. Flooding in the upper part of the basin within Bihar is responsible for more than one-half of India’s annual flood toll. There is generally some damage each year from flooding, but major flood events occurred in 1890, 1898, 1899, 1922, 1924, 1954, 1974, 1978, 1987, 1988, 2003, 2010, 2013, 2017, and 2023, for example. In 1987, floods resulted in more than 400 deaths, the destruction of 70,000 homes, and damage to another 350,000 homes. The government of Bihar blamed the apparent recent increase in flooding in the region on Nepal, arguing that deforestation of upstream regions led to higher levels of runoff and flooding of the downstream basin.

Flooding is also common in the lower reaches of the Ganges and Brahmaputra Rivers. The land in the delta area of Bangladesh is only a few meters above sea level, and when the rainy season arrives, the area is commonly inundated under 1 meter or more of water. To protect against these annual floods, many of the villages and homes are built upon hills that have been constructed by the local people. The delta area is also hit by cyclonic storms that come out of the Bay of Bengal. These storms wreak havoc on the low-lying areas. A cyclonic storm in November 1970 resulted in catastrophic flooding and caused more than 200,000 deaths.

Water Resources

The Ganges River is a major water resource for the northern and eastern portions of India. It has been utilized for drinking water, transportation, and waste disposal for thousands of years. The waters of the great river have been diverted for irrigation purposes for hundreds of years. However, the great surge in population growth in India and Bangladesh has placed huge demands on the river system. India’s heavy upstream use of freshwater for irrigation has dramatically reduced river flow for irrigation in Bangladesh and through the delta to the ocean. The loss of freshwater flow to the delta has resulted in a landward migration of seawater, leading to the salinization of the coastal lands.

The Ganges River basin is shared by Nepal, India, and Bangladesh, and water rights questions have arisen concerning the share of water to which each country is entitled. The greatest conflict resulted when India built a barrage at Farakka in the early 1970s to divert water to Kolkata. The diversion facilitated transportation to the city but, in turn, reduced river flow into Bangladesh. The Bangladesh government began a series of negotiations with the Indian government in order to obtain an equal share of the Ganges water. After many frustrating years, the two governments were finally able to craft a water-sharing agreement in 1996 that gave each country a 50 percent share of the water. Still, water shortages have become an important problem in the region.

Environmental Concerns

In addition to water use and water rights, water pollution is a major concern throughout the Ganges basin. The large population bordering the river and the lack of strong sanitary infrastructure have caused the Ganges to become heavily polluted with sewage, agricultural and industrial waste, and other debris. Complicating the problem is the river's spiritual nature to many Hindus, as cremation rites and religious offerings bring further contaminants to the water. The level of fecal coliform bacteria in the river at Varanasi is often measured at tens of thousands of times higher than the 500 per milliliter limit set by the Indian government. Such polluted conditions directly threaten the health of millions of people who rely on the river for drinking, bathing, cooking, and cleaning.

The development and pollution of the Ganges also negatively affects the wildlife in and around the river. The once large forested areas in the Indo-Gangetic Plain were largely destroyed as the human population grew in the twentieth century (and even before) and took over more land for habitation and cultivation, restricting large species such as the Bengal tiger to small protected areas. Aquatic species have also suffered, with dam construction as well as pollution reducing the numbers of notable species such as the Ganges River dolphin.

Major efforts have been made to clean up the Ganges and reduce the introduction of new pollutants. At the national level, 1986 saw the introduction of the Ganga Action Plan (GAP). This agency, created by Indian prime minister Rajiv Gandhi, was intended to coordinate clean-up initiatives along the length of the river. However, despite completing some projects, the effort was largely deemed a failure. GAP was replaced by the National Ganga River Basin Authority (NGRBA) in 2009. This successor organization, too, was often regarded as ineffective. In 2014, the administration of Indian prime minister Narendra Modi launched a new plan to clean up the Ganges called the Namami Gange program. The program promised to build over 170 sewage facilities and an estimated 5,200 kilometers of sewer lines to reduce pollution in the Ganges and its tributaries. By the 2020s, Modi's efforts were largely seen as successful, with new sewage treatment plants significantly improving the treatment of wastewater before it enters the river and additional facilities continuing to be constructed.

Climate change is also considered a significant threat to the Ganges River ecosystem. Scientists have suggested that the Himalayan glaciers that generate the source of the river are at risk due to global warming. The river's flow, runoff, and flooding are all susceptible to extremes due to climatic changes, potentially increasing the risk of property damage and loss of life. Additionally, larger-scale effects of climate change could cause significant shifts in population density and land use that may further strain an already fraught ecological situation.

Principal Terms

avulsion: a natural change in a river channel, usually caused by flooding and excess deposition of sediment

base flow: the natural flow of groundwater into a river, which commonly maintains the minimum flow of perennial rivers during the dry season

capacity: the total amount of sediment a river or stream can transport at a given time

competency: a measure of the largest particle that a river can carry at the time of measurement

delta: a landform created when a river enters a relatively still body of water and deposits much of the sediment it was transporting; deltas may form in lakes and ponds, but the largest deltas form where a silt-laden river flows into the ocean

discharge: the volume of water flowing past a measurement point in a river during a given time interval, usually measured in cubic meters per second

distributary: a river that diverges from the main river and carries and distributes the flow of water across a delta

suspended load: the total amount of sediment carried in suspension by moving water in a river, measurable over any time period but commonly determined on an annual basis

tributary: a stream or river that flows into another stream that becomes the main stream; a tributary may be a significant river in its own right, but it loses its identity when it merges with the main river

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