Towards the use of acoustic monitoring in karst networks to infer hydrological dynamics during flood events

Monitoring flood events in caves is a significant challenge due to the high energy and destructive nature of floods, which pose risks to submerged sensors and data transmission systems. This has resulted in a scarcity of studies focusing on flood propagation and its effects on air–water interactions. Notably, previous research has largely overlooked the integration of acoustic monitoring with traditional hydrological parameters. This study addresses this knowledge gap by testing a multiparametric hydrological and acoustical monitoring within Spurga delle Cadene (Lessini Mountains of Verona, Italy). This cave acts as temporary overflow karst spring with high water discharge during flood events. Infra-to-audible sound acoustic alongside water level and air pressure monitoring was employed to investigate the hydraulic functioning of the cave-spring system. Integrating these different methodologies revealed that the compression, isolation, and subsequent release of trapped air volumes in various cave compartments fundamentally influence water-level rise, pressure evolution, and flood propagation, through a newly identified process called the “Plunger Chamber Effect”. Additionally, a detailed analysis of low frequencies (<50 Hz) revealed specific repetitive acoustic patterns that consistently preceded the flood rise and accompanied its recession. These sounds are related to the release of air pockets associated with conduit morphologies and water levels. Identifying these repetitive sound patterns paves the way for the deployment of cave-specific early warning flood alert systems. This case study not only underscores the importance of integrating acoustic monitoring with classical hydrological methods providing a more comprehensive understanding of flood mechanisms in subterranean environments.