People living in the Cheyyar River Basin, in the Thiruvannamalai district of Tamil Nadu, depend primarily on agriculture. Rainfall here is rarely more than 1000 millimetres per year. The river swells up during the rainy season and quickly recedes after the rains. So the technology for extracting water from deep underground was a boon and the basin became an important agricultural hub of Tamil Nadu.
But the boon soon turned to a curse as the groundwater aquifers are now being rapidly depleted. There may come a time when people in the region will not have water to drink, let alone water for irrigation.
The region has hard-rock aquifers. So the percolation of rainwater to the aquifers is slow. Managed aquifer recharge is the only way for people in the region to avoid a disaster.
There are methods to reduce surface runoff, increase infiltration and restore groundwater: check dams, gully plugs, subsurface dykes, farm ponds, percolation tanks…
But which of these methods should we use and where?
Researchers from Vellore Institute of Technology started investigating. They listed parameters that could influence groundwater recharge. To identify whether the parameters selected were redundant, they employed a two-step multicollinearity analysis.
If a pair of two parameters was correlated, then one was removed, and the multicollinearity analysis was repeated. If more than two parameters were correlated, then collinearity diagnostics were carried out, where highly correlated parameters were identified, and one of the parameters from each pair was removed. And the analysis was rerun.
Thus, the researchers could identify 20 non-redundant parameters. This helped reduce the redundancy of parameters and the need to assign weightage based on non-explicit weighting method.
The researcher collected data on these 20 parameters from satellite and geospatial data hosted by the United States Geological Survey, the Geological Survey of India, the Indian Meteorological Department, the Environmental Systems Research Institute, State Ground and Surface Water Resources Data Center, Meteorological and Oceanographic Satellite Data Archival Center and the World Reference Base for Soil Resources.
All parameters were processed in a GIS platform for analysis. As all the data used have different units of measurement, they have to be brought to a uniform scale for comparison. This is done through normalisation.
The researchers used hydrological principles to define the ideal baseline during normalisation. For example, the lower the slope, the higher the chances for recharge. So a slope of zero degrees is used as an ideal baseline for the slope layer. In contrast, the higher the rainfall, the better the chances for greater groundwater recharge. So, for rainfall, maximum rainfall is set to the ideal baseline.
Then, the researchers used the grey relational analysis algorithm, which measures the similarity and relationship between data sequences, and extracted a final grey relational grade for every location. Higher the grade value, the better the location for groundwater recharge.
“The process adopted by us reduced the errors that creep in while giving weightage to environmental variables”, says Sundarapandian Venkatesh, Vellore Institute of Technology, Vellore.
“It also removed over-reliance on any variable in identifying potential recharge zones”, adds his supervisor, Sundaram Parimalarenganayaki.
The researchers could thus identify locations where groundwater recharge interventions can be constructed as well as the best-suited intervention for each location.
They suggest 53 farm ponds on the eastern side of the Cheyyar basin, and 30 subsurface dykes mostly around the river.
On the north and central east side of the basin, 16 percolation tanks need to be constructed.
Around the western side of the basin, 11 bench terraces, 11 gully plugs, and 10 check dams on the eastern side are needed.
On the north of the river, the researchers suggest 9 percolation ponds.
As these are mapped in geospatial software, people in the region can find the exact location and mitigate the threat of groundwater depletion. District authorities need to allocate funds to construct groundwater recharge structures at the locations identified by this research.
Agricultural Water Management 333: 110548 (2026);
DOI:10.1016/j.agwat.2026.110548
Reported by Khushbu Birawat
Environmental Consultant, Bangalore
STEAMindiaReports 
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