Preprints
https://doi.org/10.5194/egusphere-2022-326
https://doi.org/10.5194/egusphere-2022-326
 
16 May 2022
16 May 2022
Status: this preprint is open for discussion.

Assessing the relationship between weather conditions and rockfall using terrestrial laser scanner to improve risk management

Tom Birien and Francis Gauthier Tom Birien and Francis Gauthier
  • Centre d’étude nordiques (CEN) – Laboratoire de géomorphologie et de gestion des risques en montagne (LGGRM) – Université du Québec à Rimouski (UQAR), Rimouski, Canada

Abstract. Since 1987, more than 13,200 rockfalls have been inventoried by the Québec Ministry of Transport (MTQ) as having impacted the National Road 132 in northern Gaspésie. This natural hazard represents a nearly permanent danger for users. Traditional mitigation measures can be ineffective on poorly consolidated, deformed and highly fractured rockwall such as those found in northern Gaspésie. To address this issue, implementing a preventive risk management based on the factors that trigger rock instabilities could be the most effective method. Earthquake, rainfall and freeze-thaw cycles are commonly considered to be the main rockfall triggering factors. This study aims to better understand the climatic conditions conducive to rockfalls in northern Gaspésie in order to provide knowledge to implement an appropriate risk management strategy. Three rockwalls were scanned with a terrestrial laser scanner (TLS) during specific pre-targeted weather conditions. Over a period of 18 months, 17 surveys have allowed to identify 1287 rockfalls with a magnitude above 0.005 m3 on a scanned surface of 12 056 m2. In addition, meteorological instruments and a 550 cm thermistor string have been installed directly on a vertical rockwall. It appears that some weather conditions influence occurrence, frequency, and magnitude of rockfalls. In winter, rockfall frequency is 12 times higher during a superficial thaw than during a cold period in which temperature remains below 0 °C. In summer, rockfall frequency is 22 times higher during a heavy rainfall event than during a period mainly dry. Superficial freeze-thaw cycle (< 50 cm) causes mostly a high frequency of small magnitude events while deeper spring thaw (> 100 cm) results in a high frequency of large magnitude events. Influence of weather conditions on rockfall frequency and magnitude is crucial in order to improve risk management since large magnitude events represent higher potential hazards. This study provides a classification of weather conditions based on their ability to trigger rockfalls of different magnitudes. This knowledge could be used to implement a risk management strategy.

Tom Birien and Francis Gauthier

Status: open (until 10 Jul 2022)

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Tom Birien and Francis Gauthier

Tom Birien and Francis Gauthier

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Short summary
On highly fractured rockwall such as those found in northern Gaspésie, most rockfalls are triggered by weather conditions. This study highlights that in winter, rockfall frequency is 12 times higher during a superficial thaw than during a cold period in which temperature remains below 0 °C. In summer, rockfall frequency is 22 times higher during a heavy rainfall event than during a period mainly dry. This knowledge could be used to implement a risk management strategy.