Guwahati: Two weeks after devastating floods killed at least 89 people and affected several lakhs of people in Upper Assam, Assam Chief Minister Himanta Biswa Sarma has sparked the debate over illegal coal, stone and sand mining along the Assam-Nagaland border, saying people living in some of the worst-affected areas depend on mining and must decide whether such activities should continue.
The remarks, made after Sarma visited flood-ravaged villages in Sivasagar district on August 4, have renewed scrutiny of what caused one of the worst floods to hit parts of Upper Assam in over seven decades. While opposition parties have blamed decades of illegal coal, stone and sand mining in Nagaland’s hill catchments and downstream areas of river Dikhow for aggravating the disaster, the chief minister stopped short of drawing that conclusion, instead calling for a scientific assessment.
“All the people in those affected places depend on mining. So, I have requested the public to give a decision,” Sarma told reporters.
He said Assam had no authority to stop mining activities taking place in neighbouring Nagaland.
“Assam cannot go and stop mining in Nagaland. At the most, we can stop the stone crushers at Bihubor. Coal mining also does not take place in Assam; it happens in Nagaland. We cannot dictate what policy the Nagaland government will take,” he said.
Sarma added that the Assam government would take up the matter with Nagaland through the Centre.
“We will try to talk to Nagaland through the central government. No illegal mining takes place inside Assam. I will try to hold discussions myself once the flood situation improves,” he said.
However, when asked whether mining was responsible for the scale of destruction witnessed this year, the chief minister declined to make a direct link.
“Rain occurs every year, but such a flood has never happened. Satellite data will have to be studied, and institutions like IIT will have to be roped in. We politicians cannot comment so easily,” he said.
His remarks come against the backdrop of growing evidence that the July floods may have been driven by long-term ecological degradation in the Naga Hills and across the Dikhow river basin, rather than by a single extreme weather event.
Soon after the floods, the Assam government attributed the disaster to exceptionally heavy rainfall caused by a cloudburst in the Naga Hills. The India Meteorological Department (IMD), however, said there was no cloudburst in the region.
Another theory—that floodwaters resulted from the release of excess water from the Dikhu Hydroelectric Project—also failed to withstand scrutiny. The 186 MW project has not been commissioned, with construction yet to be completed because of unresolved land disputes.
Attention has increasingly shifted to the upper catchments of rivers flowing into Upper Assam, where decades of coal mining, riverbed stone extraction, hill cutting and deforestation has steadily altered the hydrology of the region.
The Dikhow River, known as the Dikhu in Nagaland, originates near the Zunheboto-Kiphire divide and flows through Zunheboto, Mokokchung, Longleng and Mon districts before entering Assam near Naginimora and joining the Brahmaputra.
The river basin includes Nagaland’s principal coalfield around Borjan and Kongan-Tiru, where coal has been extracted since 1907. Rat-hole mining continues in Borjan, while open-cast mining dominates parts of Upper Tiru. Overburden from open-cast mines is often dumped along nearby slopes instead of being scientifically managed, while large-scale extraction of boulders and gravel continues from the Dikhow riverbed.
Environmental researchers have long argued that these activities have reduced the catchments’ ability to absorb rainfall while increasing sediment flowing into rivers downstream.
Professor Arup Kumar Sarma, hydrologist and professor of civil engineering at the Indian Institute of Technology (IIT) Guwahati, said developmental activities in hilly areas can significantly alter flood behaviour downstream if carried out without adequate hydrological assessment or ecological safeguards.
According to him, extensive deforestation in upstream catchments caused by mining, road construction and other infrastructure projects has increased runoff and sediment yield, while sediment deposition has progressively reduced rivers’ carrying capacity.
He also pointed to increasingly intense rainfall associated with climate variability.
“We are experiencing high intensity rainfall due to climate change… Continuous precipitation causes land saturation and a high intensity precipitation over saturated deforested land generates high water yield,” he said.
Professor Abani Kumar Bhagabati, geographer at Gauhati University, has similarly identified deforestation and unplanned hill cutting as major contributors to worsening floods in Assam.
Hydrologists say forests regulate runoff by allowing rainwater to infiltrate the soil. When forest cover is removed, water flows rapidly over the surface, increasing erosion, landslides and sediment transport into rivers. Over time, this sediment accumulates within embanked river channels, raising riverbeds and reducing their capacity to carry floodwaters safely downstream.
During the July floods, several rivers crossed previous Highest Flood Levels despite rainfall remaining within historical ranges.
Opposition parties and civil society organisations argue that the disaster was therefore not simply the result of heavy rainfall but the cumulative outcome of decades of environmental degradation.
The Congress, Raijor Dal, Assam Jatiya Parishad and the Krishak Mukti Sangram Samiti have alleged that illegal coal and stone mining in the Assam-Nagaland border areas, coupled with political patronage, contributed to what they described as a “man-made” disaster.
Former Nazira MLA Debabrata Saikia has repeatedly raised the issue over the past several years.
In 2019, Saikia filed a public interest litigation before the Gauhati High Court seeking a ban on illegal sand and stone mining in the Dikhow River. The petition warned that continued extraction would render the river shallow and increase the risk of catastrophic flooding and erosion in Sivasagar and Nazira.
Later that year, the High Court directed the Assam government to constitute a dedicated Mines and Mineral Task Force Battalion to curb illegal mining and form a high-powered committee to protect the Dikhow’s ecosystem.
“But these directives were never implemented,” Saikia has said.
He also told the Assembly in 2022 that continued mining could eventually turn the Dikhow into a “sea-like” expanse during floods.
In August 2025, residents of Nazira publicly alleged that illegal stone and boulder mining was already aggravating erosion around Simaluguri and Tetaliguri, while an embankment-cum-road linking Tetaliguri and Masterchuk had been washed away.
Those warnings gained renewed significance after this year’s floods devastated large parts of Sivasagar and Charaideo districts, particularly along the Assam-Nagaland border.
Despite acknowledging that Assam cannot regulate mining activities inside Nagaland, Sarma’s remarks have brought the issue back into the political spotlight, reopening questions over whether stronger inter-state coordination, stricter environmental regulation and long-delayed action against illegal extraction could have reduced the scale of the disaster.
Meanwhile, the chief minister visited relief camps and flood-hit villages across Sivasagar, including Rajabari, Dihirgaon, Dhai Ali-Darikhat, Kakpathar-Kukurpuhia and Banmukh. Travelling by rubber boat, he also visited marooned areas such as Panbecha, Hatimuria, Betena, Dhupaboria, Tatipathar and Luruki to assess the damage and interact with affected residents.
Sarma said government teams would begin visiting affected households beginning August 9 to conduct a detailed assessment of losses before compensation is disbursed.
Even as relief and rehabilitation continue, the debate triggered by the chief minister’s remarks has shifted attention back to a larger question that predates this year’s floods: whether decades of mining, deforestation and hill cutting across the hill catchments and downstream areas in Assam have fundamentally changed the way rivers in Upper Assam behave—and whether the region is now paying the cumulative price of those changes.