Quantifying the impacts of groundwater abstraction on Ganges river water infiltration into shallow aquifers under the rapidly developing city of Patna, India

Study region: Patna is located on the southern bank of the River Ganges in Bihar, India. Rapid population growth over the past few decades has driven an increase in groundwater abstraction from aquifers under the city. Study focus: This study exeplores the pumping-induced water exchange between the River Ganges and groundwater under transient conditions between 2009 and 2015, using a numerical simulation. The deterministic water exchange model within an uncertainty quantification was used to reveal the controlling factors affecting river water infiltration. New hydrological insights for the region: Modelling reveals that under baseline (eno pumping) conditions, the dominant (~ 91% of the year) flow direction is from the aquifer to the river, which reverses (~ 9% of the year) when the river stage is high. When a municipal pumping well is implemented, river water infiltration into the aquifer increases to 68% of the year. The groundwater pumping rate is found to be the most important factor affecting the river water infiltration, whilst the groundwater table level is most sensitive to the well distance from the river, followed by pumping rate. Optimizing the location, depth and pumping rate of new wells in the area could mitigate fluvial contamination of the aquifer and help maintain groundwater levels.