Relationships between River and Groundwater Flow in an Alluvial Plain by Time Series Analysis and Numerical Modeling

Alluvial plains represent hydrological systems where the aquifer and the associated stream network are in hydraulic communication. In many instances, the stream network is the primary factor controlling water table variability and groundwater circulation. When effective meteoric recharge is scarce, water inflows from the river allow for aquifer exploitation by pumping wells. In addition, the river affects the propagation of the cone of depression and may limit its expansion. The study aimed to characterize the groundwater circulation in the Benevento Plain (southern Italy), which is affected by anthropogenic stresses due to pumping and aquifer-river interactions. To this end, we combined several methods to maximize the information achievable from hydrological monitoring, involving time series analysis and analytical models. We employed cross-correlation and time series processing to assess whether river flow variability could explain the observed water table variability. We also performed numerical simulations to investigate the specific contributions of aquifer-river interactions, effective meteoric recharge, and pumping to groundwater circulation. The simulations showed that the pumped groundwater comes partially from the river and that the latter represents a strong hydrological boundary, which limits the expansion of the cone of depression induced by wells. Analyses highlighted that the river controls groundwater variability and circulation in the Benevento Plain, while meteoric recharge has a negligible role. These findings are crucial for managing and protecting the local aquifer, which supplies water to one of the main inland areas of the southern Apennine, and they could be useful for other similar area worldwide.