NEW DELHI: A new study has set off alarm bells on the health and flow of river Ganga. It has found that the summer water flow in the river is severely depleted, so much so that there may be hardly any flow in the non-monsoon months in large stretches of the river from Varanasi to Kolkata in the coming years, the study published in Nature’s Scientific Reports recently has predicted.
The base-flow (groundwater inflow) into the river may have decreased by 50% from the beginning of irrigation days in the 1970s, mainly a result of indiscriminate extraction of groundwater. In next 30 years, the report suggests that groundwater contribution can decrease by up to 75% compared to 1970s in the non-monsoon months. This also means that pollution levels may rise further as there will hardly be any dilution of the sewage and other pollutants that drain into the river and remain concentrated.
“In the coming decades, the river will become non-existent in many stretches. It is a catastrophic scenario but we see it happening if immediate steps are not taken to control groundwater extraction in 2-3 km zone of the river. This will affect river life and ecology and lives of communities dependent on the river for irrigation, for drinking water, even industries will be impacted,” said Abhijit Mukherjee, associate professor of geology and geophysics at IIT Kharagpur and lead author of the study.
The authors said that there are many reports which have indicated that the river is drying but no quantitative information was available on these trends. Some studies have also suggested that climate change could be impacting flow. This study, however, used long-term satellite data, hydrological modeling, hydro-geochemical and isotope studies to arrive at how much base flow was decreasing and how much groundwater had been extracted. The level of groundwater depletion rate is the range of 0.5 to 38.1 cm/year between the summer of 1999 and 2013, according to the study.
“We looked at 28 locations through satellite data. Around 19 locations showed severe depletion trends. In some areas, the aquifers are drawing river water because there is no groundwater at all. This is called streamflow capture,” added Mukherjee. Areas around Varanasi, eastern Bihar and downstream of Farakka barrage in West Bengal are worst affected.
Authors of the report – Mukherjee, Soumendra Nath Bhanja and Yoshihide Wada of International Institute for Applied Systems Analysis (IISA), Austria – also noted in the study that “such streamflow reduction due to intense groundwater pumping is of utmost concern during low flow seasons like pre-monsoon season in Ganga basin … the depletion in river water volume will also have a profound effect on future food security in Ganga basin – the breadbasket of South Asia. The highly productive Indo-Gangetic basin would experience a substantial reduction in food production if groundwater continued to be extracted in current unsustainable rate.”