Over the past four decades, the rivers in the Himalayan foreland basin, once the vibrant lifelines of the plains, are steadily vanishing, a new study has found.
The study says that rivers such as the Raidak, the Teesta, the Mahananda, the Kosi and the Ghaghara are progressively drying up in the foothills of north Bengal, threatening ecosystems, livelihoods and water security in the region.
The findings come from a doctoral thesis by Jiarul Alam, supervised by Deepak Kumar Mandal, a professor in the North Bengal University’s geography department.
Conducted with research scholar Sanjoy Barman and Pankaj Singha, the work combined remote sensing, GIS tools and machine learning to track the transformation of the Raidak river basin.
The study revealed that between 1985 and 2024, areas capable of holding water for three to six months shrank by 2,900 acres, while short-term water zones expanded by 3,550 acres.
“This shrinking hydro-period signals a weakening of rivers’ seasonal water-holding ability,” said Alam.
Data points to an alarming increase in population and human activities, making the ecologically fragile area more vulnerable.
Land use and land cover (LULC) data between 1992 and 2024 further highlighted that swamps decreased by 5,400 acres, water bodies decreasd by 5,200 acres and vegetation by 13,700 acres.
Meanwhile, agricultural land expanded by 15,600 acres and built-up areas by 8,700 acres.
Nearly 25,700 acres of abandoned riverbeds have been converted into farmland, and 21,200 acres into settlements.
“These abandoned river channels once functioned as reservoirs and biodiversity hotspots. Their loss is a warning sign of irreversible ecological change,” Alam said.
Vulnerability mapping of the area showed that about 22,339 acres of abandoned channels are under extreme environmental risk, while another 20,215 acres are highly vulnerable. Field evidence and drone imagery confirmed that most channels have dried completely, with only a few holding water briefly during monsoons. Many have been reduced to dumping grounds.
“Beyond urbanisation and climate change, dams and embankments have disrupted natural flow and sedimentation. Intensive chemical use in farming has degraded water quality, while rising siltation and soil erosion have reduced retention capacity, accelerating permanent desiccation,” said Alam.
Between 2012 and 2024 alone, swamp areas shrank by 62 sq km, water bodies by 28 sq km, and vegetation by 15.87 sq km.
During the same period, agricultural land expanded by 55sqkm and built-up areas by 51.77sqkm.
“These abandoned channels are not just wastelands they are integral to the ecological and hydrological health of the basin. If this trajectory continues, the damage will be irreversible,” Alam warned.
Mandal urged immediate intervention through wetland restoration, strict regulation of groundwater use, a ban on farming and construction on old riverbeds, and reduced chemical dependency in agriculture.
He stressed the need to enforce existing laws such as the Water Resources (Regulation and Management) Act, 2010.
“The rivers of the Himalayan foreland basin are not merely drying they are being erased from the landscape. This loss threatens not only biodiversity but also human survival, food security, and disaster resilience,” Mandal said.