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

Abstract

Abstract Alluvial plains represent hydrological systems where the aquifer and the drainage network are strictly in hydraulic communication. In many instances, the stream system represents the primary factor controlling the water table variability and groundwater circulation. When meteoric recharge is scarce, the stream system allows for the aquifer exploitation by pumping wells and affects the propagation of the depression cone by limiting its expansion. In this context, the water table mainly responds to stream discharge variations over time rather than the meteorological input, and this response is smoothed and delayed as the alluvial aquifer acts as a low-pass filter. In this study, we applied statistical methods and numerical modeling to characterize the relationships between the groundwater and the surface-water systems in the Benevento Plain (southern Italy). Time series decomposition and correlation analysis were used to assess whether river flow variability can explain water table variability. Furthermore, the numerical model allows for understanding the specific contribution of the river, meteoric recharge, and pumping on groundwater circulation. Our analysis highlighted that the river controls the overall groundwater circulation and that pumping and meteoric recharge have limited effects. Therefore, abstracted groundwater by pumping has a direct connection with the river. The findings presented in this study are crucial in managing and protecting the Benevento Plain aquifer, which is exploited for both industrial and drinking purposes.