A recent study challenges the long-held belief that glaciers are the primary source of the Ganga River’s summer flow, revealing that groundwater plays a significantly more crucial role. The study, published in Hydrological Processes, highlights that groundwater discharge increases the Ganga’s volume by approximately 120% in the Gangetic Plains compared to its origin.
Abhayanand Singh Maurya, a professor at IIT Roorkee and author of the study, noted that while glaciers and snowmelt contribute substantially in the upstream regions, their impact diminishes beyond the Himalayan foothills. His earlier research in 2011 in Rishikesh indicated that glacial melt accounted for only about 32% of the river’s total flow, prompting him to investigate the source of the remaining water in the plains.
The Ganga, vital for various ecosystems and a lifeline for over 400 million people, faces threats from shrinking glaciers due to climate change. A separate study by IIT Indore revealed that the Gangotri glacier, the Ganga’s source, has lost 10% of its snowmelt flow over the past four decades. Despite these concerns, Maurya’s research underscores the critical importance of groundwater recharge for maintaining river health.
The study involved collecting water samples from 32 locations along the Ganga and its major tributaries before the 2019 summer monsoon. By analyzing oxygen and hydrogen isotopic ratios, researchers identified changes indicating groundwater discharge into the river. Maurya explained, "When the Ganga reaches the plains, from there until the 1,200-kilometre stretch where it meets major tributaries such as the Ghaghara and Gandak, the river is mostly groundwater-fed."
While these findings are significant, Abhijit Mukherjee, a geology professor at IIT Kharagpur, pointed out that the role of groundwater in the Ganga’s flow has been a subject of research since 2000. He stated that publications since 2006 have demonstrated the Ganga’s reliance on groundwater, with inputs ranging from 52-58% in Varanasi to as high as 75% or even 100% in parts of West Bengal during summer. Mukherjee attributed the common perception of glaciers as the main source to their visibility, contrasting with the "mostly invisible" groundwater input.
Environmentalist Ravi Chopra emphasized that while glaciers make the Ganga perennial, they aren’t substantial enough to be the primary source for its entire 2,525-kilometer course. He explained that rainfall in the catchment and surrounding hills constitutes the main flow.
Ruchi Badola, Dean at Wildlife Trust India and principal investigator for the National Mission for Clean Ganga-WII Programme, confirmed that groundwater has been a focus in their action plans, particularly supporting local communities in conserving catchments to recharge groundwater. She also highlighted the importance of groundwater for tributaries, citing the Yamuna as an example where flow becomes negligible without tributary contributions.
The study also revealed a worrying issue: the Ganga loses over half its water to evaporation in its middle plain region. This, combined with declining flow trends and severe droughts in recent decades, paints a concerning picture. Maurya identified over-extraction of groundwater, glacial retreat, excessive diversion, reduced inflow from smaller tributaries, human encroachment, and the dumping of materials as key disruptors.
Chopra stressed that no more than 50% of the river’s natural flow should be diverted and criticized existing rejuvenation programs like Namami Gange for focusing solely on cleaning without addressing river flow.
To sustain the Ganga, Maurya advocates for prioritizing groundwater recharge, understanding aquifer behavior, and maintaining the health of all tributaries. Badola supported this, highlighting programs for rainwater harvesting and rural water security.
Maurya further noted that many Indian rivers, including the Gomti, are primarily groundwater-fed outside the monsoon season, underscoring the broader need for better groundwater management.
The study recommends increasing water release from dams and barriers to 20-25% at key locations, halting untreated sewage discharge, and curbing traditional dumping practices. The National Green Tribunal (NGT) has initiated proceedings based on this study, directing the Union Ministry of Environment, Forest and Climate Change (MoEFCC) to respond to its findings.
