Dhansiri River: Origin, Tributaries, Course, Significance and Role in the 2026 Assam Floods

The Dhansiri River is one of the significant rivers of Northeast India, being one of the major southern tributaries of the Brahmaputra. Running through the regions of Nagaland and Assam, the Dhansiri River is vital for the agriculture, biodiversity and various ecosystems along its path.

Moreover, the Dhansiri River has been in the spotlight of the 2026 floods of Assam, where the excessive monsoon rainfalls in the upper catchments led to increased water levels and caused the floods in Assam. The knowledge about the origin, course, tributaries and ecological significance of the Dhansiri River will help understand the reasons for the significant effect of the change of water levels on the lower courses.

Origin of the Dhansiri River

The Dhansiri River originates in the Laisang Peak region of Nagaland at the height of about 800 m above mean sea level. The Dhansiri River is one of the major southern tributaries of the Brahmaputra River.

The course of the Dhansiri is rather long and equals approximately 352 km, and its drainage area equals 12,200 square km. The Dhansiri River was also historically known under the name Khe-Nam-Ti-Ma, especially in relation to the Ahom period.

From the mountains, the Dhansiri flows first through the hills and then into the plain of Assam.

Course of Dhansiri River

The Dhansiri takes an active course as it moves from the hills of Nagaland to Brahmaputra.

The initial course of the river flows to the north-western direction for about 40 kilometres through the hilly areas of Nagaland.

After that, the river changes direction and begins moving to the north direction where it becomes the natural dividing line between Karbi Anglong of Assam and the areas of Nagaland such as Dimapur and Chümoukedima.

In Assam plains, the river becomes very important for the district of Golaghat. In the further course, the river flows downstream till Dhansirimukh where it merges with the Brahmaputra river at the southern banks.

The river becomes relatively wide in the lower course, the downstream average width is about 150 meters.

Major Tributaries of the Dhansiri

The Dhansiri river basin has many tributaries and small seasonal streams which are feeding the river in monsoon period.

Left-bank tributaries

Among the left-bank tributaries the following rivers are,

• Langlong river
• Dhansiri (south)
• Diphu river or Diphupani
• Seasonal streams of Karbi Anglong

Right-bank tributaries

Among the right-bank tributaries, there are the following rivers,

• Dayang river (the largest tributary)
• Khora river
• Beopani river
• Kaliani river

These tributaries drain the surrounding hills and bring a lot of runoff to the Dhansiri river.

Why is the Dhansiri River important?

The Dhansiri River is significant in terms of ecology, agriculture and economy.

Environmental significance

• The Dhansiri River Basin is part of a biologically diverse terrain. There are several forests within the river basin, including the Dhansiri Reserved Forest, while the catchment of the region in general is linked to the biological diversity of Assam and Nagaland.
• It hosts several types of fish and there have been over 34 fish species found within the river basin.

Agriculture and economics

• The lower basin of Dhansiri, especially near Golaghat, is a fertile agricultural region. The water of the river facilitates paddy farming and other kinds of agriculture.
• The river waters are also of importance to the industrial activity in the region, like the Numaligarh Refinery site.

Relation to Kaziranga ecosystem

• The lower Dhansiri River is also significant for maintaining the wetland around Kaziranga National Park.
• Seasonal flooding is crucial in maintaining wetlands, swamps, oxbow lakes and bils where fish and other aquatic life forms find habitat. This ecosystem provides a home to greater one-horned rhinoceros, wild water buffaloes and migratory birds.
• This means that flooding is not necessarily negative from the point of view of ecology. Seasonal flooding is an integral component of the functioning of Assam floodplain ecosystems, albeit excessive flooding may turn out to be destructive for humans.

Dhansiri River and the 2026 Assam Floods

The river became important during the 2026 July-August Assam flood events due to heavy rainfall in its upper catchment, leading to increased runoff within the riverine system.

Rainfall in the hills of Nagaland may cause large amounts of water to flow down the river within a shorter time. This is likely to exacerbate the flood risk when the water levels and rainfall become high in Assam.

Early in August 2026, increasing water levels on the Dhansiri (South) caused some alerts and emergency advisory in the vulnerable areas. There were flooding cases in parts of the Golaghat district, mainly within the Sarupathar sub-division.

Transportation routes have also been affected by flooding. Farming has been affected. Several people have been relocated to relief camps in response to the event.

Why does the Dhansiri flood so quickly?

There are various geographical and environmental reasons behind the flood risk characteristics of the river.

The upper catchment area experiences monsoon rains, while the terrain becomes steep, hence fast-flowing water into the river. The soil erosion and sediment flow may lead to river bed siltation and hence reduction in its capacity for discharging water.

In Assam’s plains, the river has bends and meanders. Monsoon floods in such cases are likely to cause substantial erosion along the banks.

Environmental problems for Dhansiri River Basin

There are many environmental threats for this river basin.

Sedimentation and soil erosion are some of them. Deforestation and random mining in the upper reaches of the basin can cause soil to run-off into the river.

Riverbank erosion is another common environmental threat. When there is heavy discharge in the rivers, it can wash out a big portion of the river bank causing the loss of farmland and displacing the people living on the banks.

Other environmental threats to the river include pollution and encroachment.