Brahmaputra River

The river carries lots of sand and mud down from the mountains.

When it reaches flat land, it slows down. It drops the sand and splits into many channels.

Dozens of streams full of sediment flow down from the Himalayas into the Brahmaputra, and the land near Namche Barwa wears away very fast. That gives the river one of the highest sediment loads per square kilometer of any river in the world, NASA says.

After the town of Pasighat, the narrow river reaches the flatter Brahmaputra Valley and slows down. Slower water cannot carry as much sediment, so it drops sand and silt in sandbars. Within a few kilometers, the channel becomes twenty times wider and splits into many crisscrossing channels: a braided river.

NASA attributes the Brahmaputra's sediment load, among the highest per square kilometer of any river and second only to the Yellow River, to dozens of sediment-rich tributaries flowing south from the Himalayan highlands and to very high erosion rates near Namche Barwa.

A MODIS image from 9 November 2020 shows the narrow channel widening after Pasighat into multiple interlacing channels: as the water slows in the flatter valley, it loses capacity to carry sediment and deposits the excess as sandbars, and within a few kilometers the channel widens twentyfold. Downstream, in the Ganges-Brahmaputra delta, a study NASA cites found that the weight of piled-up sediment makes the land sink by 2 to 3 mm a year.

Every year, the river floods. The flood water leaves rich mud on the fields.

The river also eats away its banks and builds new land in other places.

The Brahmaputra floods every year. The floods spread mineral-rich silt across nearby farmland, refilling the soil. But there is so much sediment that big boats cannot travel on many parts of the river.

In Kaziranga National Park, the river's changes are easy to see. UNESCO describes riverbanks wearing away, sediment building new land and new ponds, and grassland and woodland taking turns. Tall wet grasslands cover nearly two-thirds of the park, kept open by yearly floods and burning.

NASA noted in 2020 that annual floods replenish farmland with mineral-rich silt, while the sheer sediment volume keeps large boats off many reaches; to limit how much the narrow, shallow channels erode land and flood, authorities had launched large-scale dredging projects.

UNESCO inscribed Kaziranga National Park (42,996 ha, Assam) in 1985, under criterion (ix) for spectacular riverine and fluvial processes: bank erosion, sedimentation and the formation of new land and water bodies, with succession between grassland and woodland. Wet alluvial grasslands cover nearly two-thirds of the park and are maintained by annual flooding and burning. River migration also cost the park some 5,000 ha of forest land between 1925 and 1986.

One-horned rhinos live in the tall grass by the river. Tigers and elephants live there too.

River dolphins swim in some of the quiet lakes.

Kaziranga, on the Brahmaputra's floodplain, holds the world's largest population of Indian one-horned rhinoceroses, more than 2,000 of them, says UNESCO. Around 1900 this rhino was close to dying out, so UNESCO calls this a spectacular conservation achievement.

The park also shelters tigers, Asian elephants, wild water buffalo and bears, and it is an important stop for migrating birds. The endangered Ganges River dolphin lives in some of its closed oxbow lakes, old bends cut off from the river.

UNESCO calls Kaziranga the world's major stronghold of the Indian one-horned rhinoceros, with a population currently estimated at over 2,000, and describes saving the species from the brink of extinction at the turn of the 20th century as a spectacular conservation achievement. Other threatened species include tiger, Asian elephant, wild water buffalo, gaur, eastern swamp deer, capped langur, hoolock gibbon and sloth bear; the park has one of India's highest tiger densities and has been a Tiger Reserve since 2007.

At the junction of two bird flyways, its wetlands matter for globally threatened migratory birds, and the Endangered Ganges River dolphin occurs in some closed oxbow lakes.

In the rainy season, the river can rise fast. Never walk into flood water.

Watch rhinos and other big animals from far away.

The Brahmaputra floods every year. The US National Weather Service warns that just 6 inches (15 centimeters) of fast-moving flood water can knock over an adult, so it is never safe to walk or drive into flood water.

PlayOwl's advice for wildlife parks such as Kaziranga: follow the park's rules and guides, and watch rhinos, elephants and tigers from a safe distance.

The US National Weather Service notes that people underestimate the force of moving water: about 6 inches (15 cm) of fast-moving flood water can knock over an adult and about 12 inches can carry away most cars, so it is never safe to walk or drive into flood water.

UNESCO also notes that seasonal flooding drives many Kaziranga animals out of the park, where they are vulnerable. PlayOwl's own advice: visit protected areas with their official guides, follow park rules and keep well back from large animals.