This study presents the measurement strategy aiming at improving the understanding of processes linked to flash floods in Mediterranean catchments. Gauging flash floods using traditional gauging methods is challenging for many reasons including hazardous flow conditions (for both equipment and people), short duration of the flood events, transient flows during the time needed to perform the gauging. This study presents examples of flash flood events in the Ardèche catchment in Autumn 2014 during which field hydrologists conducted flow measurements with different technologies including non-contact methods like image-based (LSPIV) and hand-held radar gaugings. Two ungauged catchments were equipped with a permanent LSPIV data acquisition system we developed and installed, which consists of an analog video-camera driven by an industrial PC powered by Debian Linux with a dedicated application, the water level being measured with an external radar. Different sites with bridges were identified for hand-held radar gaugings and were operated during the events to validate the LSPIV measurements and to complete the knowledge of those events. Other videos from popular video-sharing websites were used to assess the discharge at different sites and at different moments. Those results proved to be consistent with data from instrumented sites on the same catchment, and were included in a post-event survey conducted at this occasion. Operational hydrometric teams also achieved measurements with traditional gauging methods. We combined all the field measurements to better understand the dynamics of the hydrological event. These study results illustrate the potential of the non-contact gauging methods and the importance of post-event surveys in the understanding of flash flood dynamics. Combining both types of additional flow observations significantly helps in reducing the uncertainties of stage-discharge rating curves and subsequent flow estimates and hydrological metrics.