Groundwater recharge sources in the Gandak alluvial aquifer, NE India : how important is leakage from irrigation canals?

Alluvial sediments in the Indo-Gangetic Basin (IGB) form one of the world’s largest
and most heavily used aquifer systems. There is clear evidence for overabstraction
and/or groundwater contamination in some parts of the IGB, but not in
others. The hydrogeology and external influences on groundwater across the
aquifer are complex and diverse. Of these influences, the role of leakage from
irrigation canals is now a fundamental part of groundwater dynamics in the IGB
aquifer. In some areas, aquifer recharge contains a high proportion of canal
leakage (Joshi et al. 2018), but in others it is much less (Lapworth et al. 2015).
The Gandak, in NE India, is a sub catchment of the IGB and provides an excellent
laboratory for studying the evolution of groundwater-river-canal dynamics in the
centre of the basin. Our study, carried out as part of the joint UK-India funded
CHANSE project, is the first detailed investigation of the hydrochemistry, stable
isotopes and residence time of groundwater in the Gandak aquifer, to quantify the
contribution of recharge to the aquifer from canal leakage, the Gandak River and
local monsoon rainfall; and to characterise groundwater flow and mixing
behaviour.