Why Assam’s rivers keep shifting: The hidden geology behind Laika–Dodhiya and Rohmoria

Dibrugarh: The relentless erosion along the upper Brahmaputra in Assam is often blamed on floods alone. However, new scientific evidence shows that the real driver lies deeper in the region’s active tectonics.

A detailed study by Girindra Bora, Tapos Kumar Goswami (Dibrugarh University) and Bashab Nandan Mahanta (Geological Survey of India) shows that large-scale river shifts in Upper Assam are guided by fault lines, crustal movement and earthquake-triggered sediment surges, not by random river behaviour.

Using historical maps from 1926 and satellite imagery up to 2022, the authors traced changes in the Siang, Dibang and Lohit rivers. They identified the 1950 Assam earthquake as a major turning point that destabilised river courses across the Mishmi fold belt.

These findings explain why erosion repeatedly returns to the same locations despite embankments and flood-control measures.

Laika–Dodhiya: A tectonic trigger behind repeated displacement

According to the authors, the Laika–Dodhiya area was once drained by minor channels such as the Dibru and Dangori and remained relatively stable until post-earthquake adjustments began to take effect.

By the 1990s, the Lohit River diverted southward, captured the Dangori channel and established a new dominant course. This avulsion transformed Dibru–Saikhowa into a river island and exposed Laika–Dodhiya to continuous erosion.

Satellite evidence presented in the study shows that settlements visible in the early 2000s are now part of the active Brahmaputra channel.

Floods in 2012, 2013 and 2017 forced repeated relocation of the Mising community. These events highlight how tectonically controlled river shifts translate directly into human displacement.

The authors emphasise that this transformation was structurally guided, not an isolated hydrological event.

Rohmoria: Fault-controlled erosion

The study notes that erosion in Rohmoria is closely linked to the Oakland–Guijan Fault. Reactivation of this fault during the 1950 earthquake caused ground subsidence. As a result, the Brahmaputra shifted southward into a broad, erosion-prone bend.

Over the last century, the riverbank has retreated by 5–6 km, erasing villages and agricultural land. More than 10 sq km has already been lost, with erosion persistently focused along the same structurally weakened stretch.

What the authors emphasise

The authors conclude that Assam’s erosion crisis cannot be addressed through embankments alone. Rivers in tectonically active zones respond to earthquakes, fault reactivation and sediment pulses over decades.

They argue that vulnerable areas like Laika–Dodhiya and Rohmoria require tectonic-aware river management, continuous satellite monitoring and planned relocation, rather than reactive disaster relief.

The study warns that unless planners begin to account for the geology beneath Assam’s rivers, erosion and displacement will remain a recurring reality.