Abstract
Abstract: Piedmont aquifers of the Po Plain are strategic resources for drinking-water supply and for the recharge of downgradient regional systems. However, the contribution of different recharge sources remains difficult to quantify where natural mountain-front processes interact with surface-water infiltration, urbanization and groundwater abstraction. Within the AMBRA project, the UNIBO unit investigated a pilot area along the Apennine piedmont margin of the Po Plain: the Reno–Lavino, Savena and Idice alluvial fans in the Metropolitan City of Bologna, which are intensively exploited aquifers and major recharge areas for downgradient systems. During the 2024–25 hydrological year, an integrated monitoring network of 30 sites was sampled, including river water, precipitation, mountain-block groundwater, intrabasin groundwater and 16 target wells in the alluvial fans. River water and precipitation were collected bimonthly, groundwater was sampled under high- and low-flow conditions, streamflow losses were measured, and tritium analyses were used to constrain residence time and flow capture. By integrating geological, hydrochemical, hydrological, piezometric and abstraction data into endmember mixing models and water-balance calculations, the study quantified recharge partitioning and pumping-induced flow redistribution, providing indications on the sustainability of groundwater abstraction. Results acheived: recharge in the Apennine pilot area is controlled mainly by local precipitation and streambed infiltration, while groundwater abstraction also induces substantial intrabasin flow capture from downgradient or deeper aquifers. Direct mountain-block recharge was negligible or at least not robustly identifiable. Recognizing intrabasin flow capture as a major component led to a revision of the initial conceptual model and supported a ternary mixing framework based on precipitation, river water and intrabasin groundwater. Recharge and flow partitioning differed among the three fan systems. In Reno–Lavino, streambed infiltration was the dominant recharge source, accounting for 45% of the water abstracted by target wells, followed by precipitation at 15%; pumping-induced intrabasin flow capture accounted for the remaining 40%. In Savena, river infiltration was also the main recharge source, (49%), followed by precipitation (12%), while intrabasin flow capture contributed 39%. In Idice, precipitation was the main recharge source (48%), followed by river infiltration (19%), while intrabasin flow capture contributed 33%. These differences reflect local controls: the high discharge and extended losing reach of the Reno River, reduced rainfall infiltration caused by urban sealing in Savena, and the greater role of agricultural and less urbanized areas in Idice. Physically based estimates were consistent with the mixing approach, with river-infiltration differences of only about 3–5%. Final volumes were 18.3–19.0 Mm³/yr from streambed infiltration, 16.9 Mm³/yr from intrabasin flow capture and 11.4 Mm³/yr from precipitation in Reno–Lavino; 2.2–2.3, 1.8 and 1.0 Mm³/yr in Savena; and 0.9, 1.5 and 4.8 Mm³/yr in Idice, respectively. The groundwater budget indicates that, even in the high-recharge year 2024–25, most recharge was offset by abstraction. Only a limited fraction remained available for downgradient outflow toward Po Plain aquifers, making current abstraction nearly sustainable but most likely vulnerable to drier years. Overall, the study shows that natural recharge and pumping-induced redistribution cannot be managed separately, as intrabasin flow capture accounts for about 30–40% of total abstraction. The project provides a transferable framework for quantifying recharge partitioning and groundwater-budget components in alluvial fans, supporting water authorities in planning adaptation strategies under future climatic and anthropogenic pressures.
Dettagli del progetto
Responsabile scientifico: Maria Filippini
Strutture Unibo coinvolte:
Dipartimento di Scienze Biologiche, Geologiche e Ambientali
Coordinatore:
Università degli Studi di MILANO-BICOCCA(Italy)
Contributo totale Unibo: Euro (EUR) 68.800,00
Durata del progetto in mesi: 24
Data di inizio
28/09/2023
Data di fine:
28/02/2026
