Mise en oeuvre d'une stratégie d'observation pour caractériser les flux hydro-sédimentaires dans un bassin versant sujet aux crues rapides de l'observatoire de la zone critique OHMCV

International audience; Mediterranean regions are prone to intense rainfall events that can lead to devastating flash floods, sometimes associated with high sediment transport. They generally occur in small catchments (less than 20 km2) that are generally ungauged. During these events, rainfall is also very variable both in time and in space and high resolution rainfall fields are necessary to understand the corresponding hydro-sedimentary response. We present a dedicated observation strategy set up in the 116 km2, Auzon catchment (Ardèche, France, OHMCV observatory) that led to the collection of a high space time resolution of rainfall, discharge and suspended sediment data set (Nord et al., ESSD, 2017). Rainfall field estimates combine rain gauges and radar data. Flooding discharges are obtained using standard discharge gauging stations and non-contact measurements: opportunistic flood gaugings using Surface Velocimetry Radar (SVR), LS-PIV (Large scale particle image velocimetry) in fixed stations or based on videos from You Tube. Discharge and suspended sediment are monitored on nested scales ranging from the plot scale to the medium-size catchment scale, allowing relating observed fluxes and diffuse sources of sediments. All these data sets provide information about flash floods space-time characteristics and associated processes that are of interest for a better management of this kind of events and for understanding associated human behavior and damages to properties. Monitoring of suspended sediments is also necessary to study the transport of nutriments and contaminants.