Editing Brahmaputra River (section)

===Hydrology===
The [[Ganges]]–Brahmaputra–[[Meghna River|Meghna]] system has the second-greatest average discharge of the world's rivers—roughly ~{{cvt|44,000|m3/s|cuft/s|abbr=on}}, and the river Brahmaputra alone supplies about 50% of the total discharge.<ref name="Hydrological Cycle Volume III">{{cite book|url=https://books.google.com/books?id=UAmCCwAAQBAJ|title=Hydrological Cycle Volume III|last1=Igor Alekseevich|first1=Shiklomanov|isbn=978-1-84826-026-9|year=2009|publisher=EOLSS Publications }}</ref><ref name="Flood Inundation Mapping of the Sparsely Gauged Large-Scale Brahmaputra Basin Using Remote Sensing Products">{{cite journal|journal=Remote Sensing|doi=10.3390/rs11050501|last1=Biswa|first1=Bhattacharya|last2=Maurizio|first2=Mazzoleni|last3=Reyne|first3=Ugay|title=Flood Inundation Mapping of the Sparsely Gauged Large-Scale Brahmaputra Basin Using Remote Sensing Products|date=2019|volume=11|issue=5|page=501 |doi-access=free |bibcode=2019RemS...11..501B }}</ref> The rivers' combined suspended sediment load of about 1.87 billion tonnes (1.84 billion tons) per year is the world's highest.<ref name="britannica"/><ref name="combinedsedimentload">{{cite book |date=2010 |title=The Geography of India: Sacred and Historic Places |url=https://books.google.com/books?id=GdKcAAAAQBAJ&pg=PA85 |publisher=Britannica Educational Publishing |pages=85– |isbn=978-1-61530-202-4 |access-date=13 November 2016 |archive-url=https://web.archive.org/web/20180806053055/https://books.google.com/books?id=GdKcAAAAQBAJ&pg=PA85 |archive-date=6 August 2018 |url-status=live }}</ref>

In the past, the lower course of the Brahmaputra was different and passed through the [[Jamalpur District|Jamalpur]] and [[Mymensingh District|Mymensingh]] districts. In an 8.8 magnitude [[1762 Arakan earthquake|earthquake on 2 April 1762]], however, the main channel of the Brahmaputra at Bhahadurabad point was switched southwards and opened as [[Jamuna River (Bangladesh)|Jamuna]] due to the result of tectonic uplift of the [[Madhupur tract]].<ref name="books.google.com">{{cite book |last=Suess |first=Eduard |date=1904 |title=The face of the earth: (Das antlitz der erde) |url=https://archive.org/details/faceearthdasant00sollgoog |publisher=Clarendon press |pages=[https://archive.org/details/faceearthdasant00sollgoog/page/n69 50]– |access-date=15 November 2015 }}</ref>

==== Climate ====
Rising temperatures significantly contribute to snow melting in the upper Brahmaputra catchment.<ref name="link.springer.com">{{cite journal |doi=10.1186/s40068-015-0043-0 |volume=4 |title=Change in snow cover area of Brahmaputra river basin and its sensitivity to temperature |journal=Environmental Systems Research |year=2015 |last1=Barman |first1=Swapnali |last2=Bhattacharjya |first2=R. K. |doi-access=free}}</ref> The discharge of the Brahmaputra River is significantly influenced by the melting of snow in the upper part of its catchment area. This increase in river flow, caused by the substantial retreat of snow, leads to a higher downstream discharge. Such a rise in discharge often results in severe catastrophic issues, including flooding and erosion.

====Discharge====
{{unreferenced section|date=June 2023}}
[[File:Naokhel At sualkuchi.jpg|thumb|Rowing competition of [[Sualkuchi]] at Brahmaputra River]]
The Brahmaputra River is characterized by its significant rates of sediment discharge, the large and variable flows, along with its rapid channel aggradations and accelerated rates of basin denudation. Over time, the deepening of the Bengal Basin caused by erosion will result in the increase in hydraulic radius, and hence allowing for the huge accumulation of sediments fed from the Himalayan erosion by efficient sediment transportation. The thickness of the sediment accumulated above the Precambrian basement has increased over the years from a few hundred meters to over {{cvt|18|km|abbr=on}} in the Bengal fore-deep to the south. The ongoing subsidence of the Bengal Basin and the high rate of Himalayan uplift continues to contribute to the large water and sediment discharges of fine sand and silt, with 1% clay, in the Brahmaputra River.

Climatic change plays a crucial role in affecting the basin hydrology. Throughout the year, there is a significant rise in hydrograph, with a broad peak between July and September. The Brahmaputra River experiences two high-water seasons, one in early summer caused by snowmelt in the mountains, and one in late summer caused by runoff from monsoon rains. The river flow is strongly influenced by snow and ice melting of the glaciers, which are located mainly on the eastern Himalaya regions in the upstream parts of the basin. The snow and glacier melt contribution to the total annual runoff is about 27%, while the annual rainfall contributes to about {{cvt|1.9|m|abbr=on}} and {{cvt|22,000|m3/s|cuft/s|abbr=on}} of discharge.<ref name="Flood Inundation Mapping of the Sparsely Gauged Large-Scale Brahmaputra Basin Using Remote Sensing Products">{{cite journal|journal=Remote Sensing|doi=10.3390/rs11050501|last1=Biswa|first1=Bhattacharya|last2=Maurizio|first2=Mazzoleni|last3=Reyne|first3=Ugay|title=Flood Inundation Mapping of the Sparsely Gauged Large-Scale Brahmaputra Basin Using Remote Sensing Products|date=2019|volume=11|issue=5|page=501 |doi-access=free |bibcode=2019RemS...11..501B }}</ref> The highest recorded daily discharge in the Brahmaputra at Pandu was {{cvt|72,726|m3/s|cuft/s|abbr=on}} August 1962 while the lowest was {{cvt|1,757|m3/s|cuft/s|abbr=on}} in February 1968. The increased rates of snow and glacial melt are likely to increase summer flows in some river systems for a few decades, followed by a reduction in flow as the glaciers disappear and snowfall diminishes. This is particularly true for the dry season when water availability is crucial for the irrigation systems.

====Floodplain evolution====
{{unreferenced section|date=June 2023}}
The course of the Brahmaputra River has changed drastically in the past two and a half centuries, moving its river course westwards for a distance of about {{convert|80|km|abbr=on}}, leaving its old river course, appropriately named the old Brahmaputra river, behind. In the past, the floodplain of the old river course had soils which were more properly formed compared to graded sediments on the operating Jamuna river. This change of river course resulted in modifications to the soil-forming process, which include acidification, the breakdown of clays and buildup of organic matter, with the soils showing an increasing amount of biotic homogenization, mottling, the coating around Peds and maturing soil arrangement, shape and pattern. In the future, the consequences of local ground subsidence coupled with flood prevention propositions, for instance, localised breakwaters, that increase flood-plain water depths outside the water breakers, may alter the water levels of the floodplains. Throughout the years, bars, scroll bars, and sand dunes are formed at the edge of the flood plain by deposition. The height difference of the channel topography is often not more than {{Convert|1-2|m|ft|0|abbr=on}}. Furthermore, flooding over the history of the river has caused the formation of river levees due to deposition from the overbank flow. The height difference between the levee top and the surrounding floodplains is typically {{Convert|1|m|ft|0|abbr=on}} along small channels and {{Convert|2-3|m|ft|0|abbr=on}} along major channels. Crevasse splay, a sedimentary fluvial deposit which forms when a stream breaks its natural or artificial levees and deposits sediment on a floodplain, are often formed due to a breach in the levee, forming a lobe of sediments which progrades onto the adjacent floodplain. Lastly, flood basins are often formed between the levees of adjacent rivers.

====Flooding====
[[File:Brahmaputra Plains in Goalpara District of Assam 857.jpg|right|200px|thumb|Flooded villages along the Brahmaputra]]
During the monsoon season (June–October), floods are a very common occurrence. Deforestation in the Brahmaputra watershed has resulted in increased siltation levels, flash floods, and soil erosion in critical downstream habitat, such as the [[Kaziranga National Park]] in middle Assam. Occasionally, massive flooding causes huge losses to crops, life, and property. Periodic flooding is a natural phenomenon which is ecologically important because it helps maintain the lowland grasslands and associated wildlife. Periodic floods also deposit fresh alluvium, replenishing the fertile soil of the Brahmaputra River Valley. Thus flooding, agriculture, and agricultural practices are closely connected.<ref>Das, D.C. 2000. Agricultural Landuse and Productivity Pattern in Lower Brahmaputra valley (1970–71 and 1994–95). PhD Thesis, Department of Geography, North Eastern Hill University, Shillong.</ref><ref>Mipun, B.S. 1989. Impact of Migrants and Agricultural Changes in the Lower Brahmaputra Valley : A Case Study of Darrang District. Unpublished PhD Thesis, Department of Geography, North Eastern Hill University, Shillong.</ref><ref>{{cite journal | last1 = Shrivastava | first1 = R.J. | last2 = Heinen | first2 = J.T. | year = 2005 | title = Migration and Home Gardens in the Brahmaputra Valley, Assam, India | url = http://scholarcommons.usf.edu/cgi/viewcontent.cgi?article=1055&context=jea | journal = Journal of Ecological Anthropology | volume = 9 | pages = 20–34 | doi = 10.5038/2162-4593.9.1.2 | doi-access = free | access-date = 5 September 2019 | archive-date = 20 April 2021 | archive-url = https://web.archive.org/web/20210420133934/https://scholarcommons.usf.edu/cgi/viewcontent.cgi?article=1055&context=jea | url-status = live }}</ref>

The effects of flooding can be devastating and cause significant damage to crops and houses, serious bank erosive with consequent loss of homesteads, school and land, and loss of many lives, livestock, and fisheries. During the 1998 flood, over 70% of the land area of Bangladesh was inundated, affecting 31 million people and 1 million homesteads. In the 1998 flood which had an unusually long duration from July to September, claimed 918 human lives and was responsible for damaging {{Convert|1600|km|abbr=on}} of roads and {{Convert|6000|km|abbr=on}} embankments, and affecting {{Convert|6000|km2|abbr=on}} of standing crops. The 2004 floods, over 25% of the population of Bangladesh or 36 million people, were affected by the floods; 800 people died; 952 000 houses were destroyed and 1.4 million were badly damaged; 24 000 educational institutions were affected including the destruction of 1200 primary schools, 2 million governments and private tube wells were affected, over 3 million latrines were damaged or washed away, this increases the risks of waterborne diseases including diarrhea and cholera. Also, {{Convert|1.1|e6ha|e6acre|abbr=unit}} of the rice crop was submerged and lost before it could be harvested, with 7% of the yearly ''aus'' (early season) rice crop lost; {{cvt|270,000|ha|abbr=on}} of grazing land was affected, 5600 livestock perished together with 254 00 poultry and {{Convert|63|e6t|e6ST|abbr=off}} of lost fish production.

Flood-control measures are taken by the water resource department and the Brahmaputra Board, but until now the flood problem remains unsolved. At least a third of the land of [[Majuli|Majuli Island]] has been eroded by the river. Recently, it is suggested that a highway protected by concrete mat along the river bank and excavation of the river bed can curb this menace. This project, named the Brahmaputra River Restoration Project, is yet to be implemented by the government. Recently the Central Government approved the construction of Brahmaputra Express Highways.