Impact of hydropeaking on groundwater flow and its implication for mixing

The influence of heterogeneity occurring in natural porous media on spreading, dilution and mixing processes has been widely recognized in the literature, while less attention has been dedicated to investigating the influence of highly transient boundary conditions on the transport of contaminants in the subsurface. Mixing in groundwater flows is inefficient, but it can be greatly enhanced by transient conditions, which are commonly encountered in the environment. For example, surface water-goundwater interaction can be significantly affected by rapid fluctuations of the river stage caused by hydropower production (hydropeaking). In this work, we focus on the Adige valley aquifer, where river discharge of the Adige River and of the Noce River varies at multiple temporal scales due to seasonal (snow and glacier melt) and anthropogenic (i.e., hydropeaking) causes. To show how such fluctuations may affect the interaction between surface water and groundwater we present both experimental data of groundwater level, temperature and electrical conductivity and a model based interpretation of the data. Our study shows that the effect of hydropeaking on surface water - goundwater interaction varies for dry and wet years with important consequeces for solute transport.