Experiences of Debris-Flow Monitoring and Warning at Catchment Scale in the Pyrenees

Debris-flow monitoring improves the understandings of debris flows and also provides fundamental information for an efficient early warning and alarm system (EWAS), which commonly focuses on ground vibration and flow depth. Preliminary results from the Senet station (Central Pyrenees, Spain) show that monitoring is a complex task, especially if different torrential processes should be distinguished using merely geophone data. Video images are not useful for an EWAS, but strongly improves the analysis, because they allow to identify the flow type and to characterise the ground vibrations corresponding to each type. In addition, an EWAS can also be based on triggering rainfall patterns, which have to be defined by a one-parameter o multi-parameter condition. Our first experiences on the possible implementation of an EWAS at Senet test site are promising, but indicate the complexity regarding the critical rainfall conditions, the definition of reliable thresholds to avoid false alarms and the difficulties related to technical shortcomings.