Quantifying groundwater recharge in the Venetian high plain between the Brenta and Piave Rivers through integrated surface-subsurface hydrological modeling

Study region: Venetian high plain between the Brenta and Piave Rivers, Northeast Italy. Study focus: Groundwater recharge is the process by which aquifers, i.e., the groundwater reservoirs, are replenished. In many regions, recharge fluxes are currently declining due to more frequent hydroclimatic extreme events and unsustainable land use management. In this study, CATHY (CATchment Hydrology), an integrated surface-subsurface hydrological model (ISSHM), is used to estimate current and future recharge fluxes in a study area that represents an important source of drinking water supply for the Treviso province (Veneto Region, Northeast Italy). In particular, we aim to evaluate the impacts on recharge of a scenario with changed irrigation management, planned in compliance with European directive indications, to decrease water withdrawals from the Piave River and preserve its ecological flow. The model was first calibrated through a combination of FePEST and the Shuffled Complex Evolution algorithm, whereby both the bottom of the unconfined aquifer and the hydraulic conductivity field were tuned. After a validation step, the resulting model was used to simulate a scenario in which the flood irrigation method, currently the most widespread in the study area, is fully replaced by sprinkler irrigation. New hydrological insights for the region: Our results show that, in response to a 50 % decrease in water withdrawn from the Piave River, the total recharge decreases by about 10 %, with a local reduction in groundwater head, mainly limited in wells located in the area directly affected by the conversion of the irrigation technique. The model suggests that most of the recharge fluxes occur in irrigated areas where the hydraulic conductivity is higher. Overall, this work resulted in the development of an ISSHM capable to reproduce groundwater dynamics and its drivers at high resolution and large scale. Although it can still be improved, the model represents a useful tool to investigate possible responses of the considered hydrosystem to future land use and climate change.