Field-Based Insights into Hydrodynamics and Sediment Transport during a Flash Flood in the San Antonio River in Argentina

This study investigates the hydrodynamic and sediment-transport dynamics during a flash flood that occurred on February 23, 2024, in the San Antonio River, a tributary of the San Roque Reservoir in Córdoba, Argentina. Such events pose a significant hazard in urban and recreational rivers; however, their transient processes remain poorly understood, particularly regarding the onset of bed-load transport and the vulnerability of exposed individuals. High-resolution, stationary measurements were collected using an Acoustic Doppler Current Profiler (ADCP), generating time series of flow depth, velocity, and energy slope during the passage of the flood wave front. Sediment mobilization was assessed through the Shields–Parker diagram, and flow conditions were compared against human body stability criteria for both adults and children. Results indicate that the velocity rise preceded the increase in flow depth, reflecting an initial adjustment of the wave-front slope. During the flood arrival, during a 22-min interval, flow depth increased from 0.40 to 1.47 m, and velocity rose from 0.20 to 2.00 m / s . Bed-load transport initiated given higher velocities with nearly constant depth, followed by sustained transport and a sharp increase in suspended sediment presence. Regarding human safety, the applied body stability criteria indicate that instability thresholds were exceeded rapidly: within only 2 min for children and 3 min for adults after the onset of the rising limb, highlighting the high vulnerability of recreational areas. These findings emphasize the value of direct, high-resolution observations to better understand unsteady processes in flash floods and to provide key insights for risk management in urban and touristic river systems.