Editing Ganges (section)

==Hydrology==
[[File:GangesValley&Plain.jpg|thumb|A 1908 map showing the course of the Ganges and its tributaries.]]
Major left-bank tributaries include the Gomti River, Ghaghara River, Gandaki River and Kosi River; major right-bank tributaries include the Yamuna River, Son River, [[Punpun]] and Damodar. The hydrology of the Ganges River is very complicated, especially in the Ganges Delta region. One result is different ways to determine the river's length, its [[Discharge (hydrology)|discharge]], and the size of its [[drainage basin]].
[[File:River Ganga with Howrah bridge in the backdrop.jpg|thumb|The River Ganges at Kolkata, with [[Howrah Bridge]] in the background]]
[[File:Lower Ganges in Lakshmipur, Bangladesh.jpg|thumb|Lower Ganges in Lakshmipur, Bangladesh]]

The name ''Ganges'' is used for the river between the confluence of the [[Bhagirathi]] and Alaknanda rivers, in the Himalayas, and the first [[River bifurcation|bifurcation]] of the river, near the Farakka Barrage and the India-Bangladesh Border. The length of the Ganges is frequently said to be slightly over {{convert|2600|km|mi|abbr=on}} long, about {{convert|2601|km|mi|abbr=on}},<ref name="Merriam-WebsterInc1997">{{cite book|author=Merriam-Webster|title=Merriam-Webster's geographical dictionary|url=https://books.google.com/books?id=Co_VIPIJerIC&pg=PA412|year=1997|publisher=Merriam-Webster|isbn=978-0877795469|page=412|access-date=15 November 2015|archive-date=28 March 2024|archive-url=https://web.archive.org/web/20240328172554/https://books.google.com/books?id=Co_VIPIJerIC&pg=PA412#v=onepage&q&f=false|url-status=live}}</ref> {{convert|2525|km|mi|abbr=on}}{{sfn|Gupta|2007|p=347}}{{sfn|Jain|Agarwal|Singh|2007|pp=334–342}} or {{convert|2650|km|mi|abbr=on}}.{{sfn|Berga|2006| p=1304}} In these cases the river's source is usually assumed to be the source of the Bhagirathi River, Gangotri Glacier at Gomukh and its mouth being the mouth of the Meghna River on the Bay of Bengal.{{sfn|Gupta|2007|p=347}}<ref name="Merriam-WebsterInc1997"/>{{sfn|Jain|Agarwal|Singh|2007|pp=334–342}}{{sfn|Berga|2006| p=1304}} Sometimes the source of the Ganges is considered to be at Haridwar, where its Himalayan headwater streams debouch onto the Gangetic Plain.{{sfn|Dhungel|Pun|2009|p=210}}

In some cases, the length of the Ganges is given by its Hooghly River distributary, which is longer than its main outlet via the Meghna River, resulting in a total length of about {{convert|2704|km|mi|abbr=on}}, if taken from the source of the Bhagirathi,{{sfn|Parua|2009}} or {{convert|2321.50|km|mi|abbr=on}}, if from Haridwar to the Hooghly's mouth.{{sfn|Dhungel|Pun|2009}} In other cases the length is said to be about {{convert|2304|km|mi|abbr=on}}, from the source of the Bhagirathi to the Bangladesh border, where its name changes to ''Padma''.{{sfn|Mirza|2004}}

For similar reasons, sources differ over the size of the river's drainage basin. The basin covers parts of four countries, India, [[Nepal]], [[People's Republic of China|China]], and Bangladesh; eleven Indian states, [[Himachal Pradesh]], Uttarakhand, Uttar Pradesh, Madhya Pradesh, [[Chhattisgarh]], Bihar, [[Jharkhand]], [[Punjab, India|Punjab]], Haryana, [[Rajasthan]], West Bengal, and the Union Territory of [[Delhi]].<ref>{{cite journal | title=The Ganges Water Machine|author1=Roger Revelle |author2=V. Lakshminarayan | journal=Science| date=9 May 1975| volume=188 |issue=4188| pages=611–16| doi=10.1126/science.188.4188.611 | pmid=17740017|bibcode=1975Sci...188..611R }}</ref> The Ganges basin, including the delta but not the Brahmaputra or Meghna basins, is about {{convert|1080000|km2|sqmi|abbr=on}}, of which {{convert|861000|km2|sqmi|abbr=on}} is in India (about 80%), {{convert|140000|km2|sqmi|abbr=on}} in Nepal (13%), {{convert|46000|km2|sqmi|abbr=on}} in Bangladesh (4%), and {{convert|33000|km2|sqmi|abbr=on}} in China (3%).{{sfn|Suvedī|2005|p=61}} Sometimes the Ganges and Brahmaputra–Meghna drainage basins are combined for a total of about {{convert|1600000|km2|sqmi|abbr=on}}{{sfn|Elhance|1999| pp=156–58}} or {{convert|1621000|km2|sqmi|abbr=on}}.{{sfn|Arnold|2000}} The combined Ganges-Brahmaputra-Meghna basin (abbreviated GBM or GMB) drainage basin is spread across Bangladesh, [[Bhutan]], India, Nepal, and China.<ref name="ServatSystems2002">{{cite book|author1=Eric Servat|author2=IAHS International Commission on Water Resources Systems|title=FRIEND 2002: Regional Hydrology: Bridging the gap between research and practice|url=https://books.google.com/books?id=9NxqSD-V-acC&pg=PA308|year=2002|publisher=IAHS|isbn=978-1901502817|page=308}}</ref>

The Ganges basin ranges from the Himalaya and the [[Transhimalaya]] in the north, to the northern slopes of the [[Vindhya]] range in the south, from the eastern slopes of the [[Aravalli Range|Aravalli]] in the west to the [[Chota Nagpur plateau]] and the [[Sunderbans]] delta in the east. A significant portion of the discharge from the Ganges comes from the Himalayan mountain system. Within the Himalaya, the Ganges basin spreads almost 1,200&nbsp;km from the Yamuna-Satluj divide along the Simla ridge forming the boundary with the [[Indus]] basin in the west to the Singalila Ridge along the Nepal-Sikkim border forming the boundary with the Brahmaputra basin in the east. This section of the Himalaya contains 9 of the 14 highest peaks in the world over 8,000m in height, including [[Mount Everest]] which is the high point of the Ganges basin.<ref name="evepkbgr">{{cite web|url=http://www.peakbagger.com/peak.aspx?pid=10640|title=Mount Everest, China/Nepal|access-date=12 March 2014|archive-date=22 February 2014|archive-url=https://web.archive.org/web/20140222035808/http://peakbagger.com/peak.aspx?pid=10640|url-status=live}}</ref> The other peaks over 8,000m in the basin are [[Kangchenjunga]],<ref name="kangchpkbgr">{{cite web|url=http://www.peakbagger.com/peak.aspx?pid=10653|title=Kāngchenjunga, India/Nepal|access-date=12 March 2014|archive-date=8 September 2022|archive-url=https://web.archive.org/web/20220908215406/https://www.peakbagger.com/Peak.aspx?pid=10653|url-status=live}}</ref> [[Lhotse]],<ref name="lhotpkbgr">{{cite web|url=http://www.peakbagger.com/peak.aspx?pid=10642|title=Lhotse, China/Nepal|access-date=12 March 2014|archive-date=15 June 2022|archive-url=https://web.archive.org/web/20220615145939/https://www.peakbagger.com/peak.aspx?pid=10642|url-status=live}}</ref> [[Makalu]],<ref name="makalpkbgr">{{cite web|url=http://www.peakbagger.com/peak.aspx?pid=10649|title=Makalu, China/Nepal|access-date=12 March 2014|archive-date=15 June 2022|archive-url=https://web.archive.org/web/20220615144432/https://www.peakbagger.com/peak.aspx?pid=10649|url-status=live}}</ref> [[Cho Oyu]],<ref name="choopkbgr">{{cite web|url=http://www.peakbagger.com/peak.aspx?pid=10634|title=Cho Oyu, China/Nepal|access-date=12 March 2014|archive-date=8 September 2022|archive-url=https://web.archive.org/web/20220908164635/https://www.peakbagger.com/Peak.aspx?pid=10634|url-status=live}}</ref> [[Dhaulagiri]],<ref name="dhaulapkbgr">{{cite web|url=http://www.peakbagger.com/peak.aspx?pid=10620|title=Dhaulāgiri, Nepal|access-date=12 March 2014|archive-date=16 April 2016|archive-url=https://web.archive.org/web/20160416200702/http://peakbagger.com/Peak.aspx?pid=10620|url-status=live}}</ref> [[Manaslu]],<ref name="manaslpkbgr">{{cite web|url=http://www.peakbagger.com/peak.aspx?pid=10627|title=Manaslu, Nepal|access-date=12 March 2014|archive-date=20 September 2013|archive-url=https://web.archive.org/web/20130920061902/http://peakbagger.com/peak.aspx?pid=10627|url-status=live}}</ref> [[Annapurna]]<ref name="annappkbgr">{{cite web|url=http://www.peakbagger.com/peak.aspx?pid=10621|title=Annapūrna, Nepal|access-date=12 March 2014|archive-date=15 June 2022|archive-url=https://web.archive.org/web/20220615151440/https://www.peakbagger.com/peak.aspx?pid=10621|url-status=live}}</ref> and [[Shishapangma]].<ref name="shishpkbgr">{{cite web|url=http://www.peakbagger.com/peak.aspx?pid=10631|title=Shishapangma, China|access-date=12 March 2014|archive-date=16 April 2016|archive-url=https://web.archive.org/web/20160416200702/http://peakbagger.com/Peak.aspx?pid=10631|url-status=live}}</ref> The Himalayan portion of the basin includes the south-eastern portion of the state of Himachal Pradesh, the entire state of Uttarakhand, the entire country of Nepal and the extreme north-western portion of the state of West Bengal.{{citation needed|date=July 2012}}

The discharge of the Ganges also differs by source. Frequently, discharge is described for the mouth of the Meghna River, thus combining the Ganges with the Brahmaputra and Meghna. This results in a total average annual discharge of about {{convert|38000|m3/s|cuft/s|abbr=on}},{{sfn|Arnold|2000}} or {{convert|42470|m3/s|cuft/s|abbr=on}}.{{sfn|Parua|2009}} In other cases the average annual discharges of the Ganges, Brahmaputra, and Meghna are given separately, at about {{convert|16650|m3/s|cuft/s|abbr=on}} for the Ganges, about {{convert|19820|m3/s|cuft/s|abbr=on}} for the Brahmaputra, and about {{convert|5100|m3/s|cuft/s|abbr=on}} for the Meghna.{{sfn|Jain|Agarwal|Singh|2007|pp=334–342}}

[[File:Hardinge Bridge Bangladesh (4).JPG|thumb|[[Hardinge Bridge]], Bangladesh, crosses the Ganges-Padma River. It is one of the key sites for measuring streamflow and discharge on the lower Ganges.]]
The maximum peak discharge of the Ganges, as recorded at [[Hardinge Bridge]] in Bangladesh, exceeded {{convert|70000|m3/s|cuft/s|abbr=on}}.{{sfn|Krishna Murti|1991|p=10}} The minimum recorded at the same place was about {{convert|180|m3/s|cuft/s|abbr=on}}, in 1997.{{sfn|Salman|Uprety|2002|p=133}}

The hydrologic cycle in the Ganges basin is governed by the [[Monsoon of Indian subcontinent|Southwest Monsoon]]. About 84% of the total rainfall occurs in the monsoon from June to September. Consequently, [[streamflow]] in the Ganges is highly seasonal. The average dry season to monsoon discharge ratio is about 1:6, as measured at [[Hardinge Bridge]]. This strong seasonal variation underlies many problems of land and water resource development in the region.{{sfn|Mirza|2004}} The seasonality of flow is so acute it can cause both drought and [[flood]]s. Bangladesh, in particular, frequently experiences drought during the dry season and regularly suffers extreme floods during the monsoon.{{sfn|Salman|Uprety|2002|p=133}}

In the Ganges Delta, many large rivers come together, both merging and [[River bifurcation|bifurcating]] in a complicated network of [[Channel (geography)|channels]]. The two largest rivers, the Ganges and Brahmaputra, both split into distributary channels, the largest of which merge with other large rivers before themselves joining the Bay of Bengal. But this current channel pattern was not always the case. Over time the rivers in Ganges Delta have often [[Avulsion (river)|changed course]], sometimes altering the network of channels in significant ways.<ref>{{cite journal|url= https://doi.org/10.1016/j.geomorph.2022.108482 |title= Island area changes in the Sundarban region of the abandoned western Ganga–Brahmaputra–Meghna Delta, India and Bangladesh |date= 2023 |doi= 10.1016/j.geomorph.2022.108482 |access-date=14 April 2024 |last1= Bandyopadhyay |first1= Sunando |last2= Kar |first2= Nabendu Sekhar |last3= Dasgupta |first3= Susmita |last4= Mukherjee |first4= Dipanwita |last5= Das |first5= Abhijit |journal= Geomorphology |volume= 422 |bibcode= 2023Geomo.42208482B |url-access= subscription }}</ref>

Before the late 12th century the Bhagirathi-Hooghly distributary was the main channel of the Ganges and the Padma was only a minor spill-channel. The main flow of the river reached the sea not via the modern Hooghly River but rather by the [[Adi Ganga]]. Between the 12th and 16th centuries, the Bhagirathi-Hooghly and Padma channels were more or less equally significant. After the 16th century, the Padma grew to become the main channel of the Ganges.{{sfn|Chakrabarti|2001| pp=126–27}} It is thought that the Bhagirathi-Hooghly became increasingly choked with silt, causing the main flow of the Ganges to shift to the southeast and the Padma River. By the end of the 18th century, the Padma had become the main distributary of the Ganges.{{sfn|Parua|2009}} One result of this shift to the Padma was that the Ganges now joined the Meghna and Brahmaputra rivers before emptying into the Bay of Bengal. The present confluence of the Ganges and Meghna was formed very recently, about 150 years ago.<ref name="Catling1992">{{cite book|last=Catling|first=David|title=Rice in deep water|url=https://books.google.com/books?id=N5JxwKx1RAgC&pg=PA175|year=1992|publisher=[[International Rice Research Institute]]|isbn=978-9712200052|page=175}}</ref>

Also near the end of the 18th century, the course of the lower Brahmaputra changed dramatically, significantly altering its relationship with the Ganges. In 1787 there was a great flood on the [[Teesta River]], which at the time was a tributary of the Ganges-Padma River. The flood of 1787 caused the Teesta to undergo a sudden change course, an [[Avulsion (river)|avulsion]], shifting east to join the Brahmaputra and causing the Brahmaputra to shift its course south, cutting a new channel. This new main channel of the Brahmaputra is called the Jamuna River. It flows south to join the Ganges-Padma. During ancient times, the main flow of the Brahmaputra was more easterly, passing by the city of [[Mymensingh]] and joining the Meghna River. Today this channel is a small distributary but retains the name Brahmaputra, sometimes Old Brahmaputra.<ref name="Britannica-Brahmaputra">{{cite encyclopedia |year=2011 |title=Brahmaputra River |encyclopedia=[[Encyclopædia Britannica]] |edition=Online Library |url=http://www.library.eb.com/eb/article-48056 |access-date=25 April 2011 |archive-date=28 March 2024 |archive-url=https://web.archive.org/web/20240328172525/https://library.eb.com/?target=%2Feb%2Farticle-48056 |url-status=live }}</ref> The site of the old Brahmaputra-Meghna confluence, in the locality of [[Langalbandh]], is still considered sacred by Hindus. Near the confluence is a major early historic site called [[Wari-Bateshwar ruins|Wari-Bateshwar]].{{sfn|Chakrabarti|2001|pp=126–127}}

In the rainy season of 1809, the lower channel of the Bhagirathi, leading to Kolkata, had been entirely shut; but in the following year it opened again and was nearly of the same size as the upper channel but both however suffered a considerable diminution, owing probably to the new communication opened below the Jalanggi on the upper channel.<ref>{{Cite book|last=Martin|first=Robert|title=The History, Antiquities, Topography, and Statistics of Eastern India. Vol-II: Bhagulpoor, Goruckpoor, and Dinajepoor |url=https://archive.org/details/in.ernet.dli.2015.283662|year=1838|pages=Book 1, Chapter 1, Page 9}}</ref>