Debris-flow monitoring stations in the eastern pyrenees. description of instrumentation, first experiences and preliminary results

Abstract

Monitored observation stations represent a fundamental tool to properly investigate the initiation, flow behaviour and accumulation of debris flows. In the recent years, tree different monitoring stations have been built up in the Eastern Pyrenees. The instrumentation of all of them consists of four geophones and a rain gauge, while two of them also have an ultrasonic device and one site a video camera. First experiences regarding the set-up and calibration of the different devices indicate that debris-flow monitoring is a complex task and requires knowledge of different research areas. In particular, quali ed electronic skills are essential. The preliminary results show that especially the Senet test site, with its initiation area in a steep and voluminous glacial deposit, presents a high debris-flow activity. Several events were recorded during the first year test phase and the analysis of precipitation data showed that most of the debris flows were triggered by short duration-high intensity rainfalls. The interpretation of the monitoring data related to the flow behaviour was not easy, because only geophone measurements, rainfall data and post-event field observations were available for the process analysis in most of the events. Thus, the visual information of a video camera is very helpful to carry out the calibration of monitoring data and to clarify doubts of interpretation.