<p>This paper presents a holistic analysis of the flash flood of September 11—15, 2019 in the Menor Sea Basin (Spain). The research aims to map the flooded area, to analyze the main causal factors and to establish criteria to detect the active zone in highly anthropized alluvial apron systems. For this purpose, several data sources were combined, including digital elevation models, orthophotos, precipitation and gauging data, geomorphological and flood risk mapping, and Sentinel-2 Level-2A surface reflectance products (Copernicus), which were interpreted using a turbidity-based water index. The results allow a comprehensive characterization of flash flood processes in alluvial fan apron systems and highlight different behaviors across different sectors of these complex fan systems. They show a significant discrepancy between observed flood processes and official hazard mapping, which underlines the need to develop quali-quantitative approaches to better understand flood processes in alluvial apron systems. The research also shows that flooding in Mediterranean alluvial apron systems should be considered as mixed processes, resulting from interactions between natural and anthropogenic factors, due to the long tradition of runoff use and management through different traditional infrastructures. Future flood mitigation strategies should recover or imitate these ancestral solutions and promote a radical shift in urban design.</p>