Groundwater thermal monitoring to characterize streambed water fluxes of the Brenta river (Northern Italy)

Abstract The work proposed deals with the characterization of temporal and spatial variability of water exchange fluxes from/to the Brenta river streambed (Veneto, Italy), critically important to regional water resources management. The aquifer system evolves from a large undifferentiated aquifer close to the adjacent mountain ranges, later developing into a well-structured multi-layer system made up of six well-defined confined aquifers constituting the noteworthy subsurface reservoirs of the area. A three-dimensional groundwater flow model of the multi-aquifer system of the Central Veneto, within a 3300 km 2 area, integrating a large amount of data, has been developed to analyze the behaviour of this large, complex and well-monitored sedimentary system. The temporal and spatial variability of the water exchange flux is investigated using heat as a tracer in conjunction with water-level measurements (in the river and in piezometers close to the river): an effective method for estimating groundwater/surface water exchanges. In the study area, 5 groundwater monitoring wells (4 on the right bank, 1 on the left bank) were drilled along the river banks near a pilot transversal ramp (permeable river barrier) built in order to reduce the downstream flooding risk and to increase the river dispersion. A hydrothermal model of the river and of the underlying aquifer was implemented to improve the estimation of the water exchange between the Brenta river and the aquifer system. The contribution of exchange between the river and the underlying aquifer is quantified by comparing simulations of water flow and heat transport to observed temperature and levels in river and in groundwater.