Laboruntersuchung zum Stabilitätsverhalten eigendynamischer Rampen

Aufsatz veröffentlicht in: "Wasserbau-Symposium 2021: Wasserbau in Zeiten von Energiewende, Gewässerschutz und Klimawandel, Zurich, Switzerland, September 15-17, 2021, Band 2" veröffentlicht unter: https://doi.org/10.3929/ethz-b-00049975

Nachweis der Wanderkorridore auf einer eigendynamischen Rampe

Aufsatz veröffentlicht in: "Wasserbau-Symposium 2021: Wasserbau in Zeiten von Energiewende, Gewässerschutz und Klimawandel, Zurich, Switzerland, September 15-17, 2021, Band 2" veröffentlicht unter: https://doi.org/10.3929/ethz-b-00049975

Physical model investigation of the transition of a debris flow from the aerial to the water phase

In order to study the phenomena of debris flow motion and deposition at the transition between a channel and an underwater storage area, experiments were carried out on a physical model. The current situation and the planned works were reproduced in two idealised 1:100 scale models. The experiments show that the flows experience an abrupt transition into water with the creation of a water wave and enter the lake undergoing a decrease in front velocity, but without creating upstream stagnation or local deposits due to the sudden phase change. Instead, the debris flows move to the lower part of the model, where they are deposited in the horizontal plane and in the lower parts of the conoid. The construction of a retention basin in the lake does not decisively influence the dynamics of the transition between the aerial and underwater phases. The results of the physical modelling provide indispensable data for the validation of the 3D numerical codes currently being tested

Physical model investigation of the transition of a debris flow from the aerial to the water phase

In order to study the phenomena of debris flow motion and deposition at the transition between a channel and an underwater storage area, experiments were carried out on a physical model. The current situation and the planned works were reproduced in two idealised 1:100 scale models. The experiments show that the flows experience an abrupt transition into water with the creation of a water wave and enter the lake undergoing a decrease in front velocity, but without creating upstream stagnation or local deposits due to the sudden phase change. Instead, the debris flows move to the lower part of the model, where they are deposited in the horizontal plane and in the lower parts of the conoid. The construction of a retention basin in the lake does not decisively influence the dynamics of the transition between the aerial and underwater phases. The results of the physical modelling provide indispensable data for the validation of the 3D numerical codes currently being tested

Stufen-Becken-Tagung: 24. Augst 2022, Zweisimmen

ISSN:0374-005

Direct observations of a three million cubic meter rock-slope collapse with almost immediate initiation of ensuing debris flows

Catastrophic collapse of large rock slopes ranks as one of the most hazardous natural phenomena in mountain landscapes. The cascade of events, from rock- slope failure, to rock avalanche and the near-immediate release of debris flows has not previously been described from direct observations. We report on the 2017, 3.0 × 106 m3 failure on Pizzo Cengalo in Switzerland, which led to human casualties and significant damage to infrastructure. Based on remote sensing and field investigations, we find a change in critical slope stability prior to failure for which permafrost may have played a destabilizing role. The resulting rock avalanche traveled for 3.2 km and removed over one million m3 of glacier ice and debris deposits from a previous rock avalanche in 2011. Whereas this entrainment did not lead to an unusually large runout distance, it favored debris flow activity from the 2017 rock avalanche deposits: the first debris flow occurred with a delay of 30 s followed by ten debris flows within 9.5 h and two additional events two days later, notably in the absence of rainfall. We hypothesize that entrainment and impact loading of saturated sediments explain the initial mobility of the 2017 rock avalanche deposits leading to a near- immediate initiation of debris flows. This explains why an earlier rock avalanche at the same site in 2011 was not directly followed by debris flows and underlines the importance of considering sediment saturation in a rock avalanche’s runout path for Alpine hazard assessments

Direct observations of a three million cubic meter rock-slope collapse with almost immediate initiation of ensuing debris flows

Catastrophic collapse of large rock slopes ranks as one of the most hazardous natural phenomena in mountain landscapes. The cascade of events, from rock- slope failure, to rock avalanche and the near-immediate release of debris flows has not previously been described from direct observations. We report on the 2017, 3.0 × 106 m3 failure on Pizzo Cengalo in Switzerland, which led to human casualties and significant damage to infrastructure. Based on remote sensing and field investigations, we find a change in critical slope stability prior to failure for which permafrost may have played a destabilizing role. The resulting rock avalanche traveled for 3.2 km and removed over one million m3 of glacier ice and debris deposits from a previous rock avalanche in 2011. Whereas this entrainment did not lead to an unusually large runout distance, it favored debris flow activity from the 2017 rock avalanche deposits: the first debris flow occurred with a delay of 30 s followed by ten debris flows within 9.5 h and two additional events two days later, notably in the absence of rainfall. We hypothesize that entrainment and impact loading of saturated sediments explain the initial mobility of the 2017 rock avalanche deposits leading to a near- immediate initiation of debris flows. This explains why an earlier rock avalanche at the same site in 2011 was not directly followed by debris flows and underlines the importance of considering sediment saturation in a rock avalanche’s runout path for Alpine hazard assessments

Direct observations of a three million cubic meter rock-slope collapse with almost immediate initiation of ensuing debris flows

Catastrophic collapse of large rock slopes ranks as one of the most hazardous natural phenomena in mountain landscapes. The cascade of events, from rock-slope failure, to rock avalanche and the near-immediate release of debris flows has not previously been described from direct observations. We report on the 2017, 3.0 × 10^6 m3 failure on Pizzo Cengalo in Switzerland, which led to human casualties and significant damage to infrastructure. Based on remote sensing and field investigations, we find a change in critical slope stability prior to failure for which permafrost may have played a destabilizing role. The resulting rock avalanche traveled for 3.2 km and removed over one million m3 of glacier ice and debris deposits from a previous rock avalanche in 2011. Whereas this entrainment did not lead to an unusually large runout distance, it favored debris flow activity from the 2017 rock avalanche deposits: the first debris flow occurred with a delay of 30 s followed by ten debris flows within 9.5 h and two additional events two days later, notably in the absence of rainfall. We hypothesize that entrainment and impact loading of saturated sediments explain the initial mobility of the 2017 rock avalanche deposits leading to a near-immediate initiation of debris flows. This explains why an earlier rock avalanche at the same site in 2011 was not directly followed by debris flows and underlines the importance of considering sediment saturation in a rock avalanche’s runout path for Alpine hazard assessments.ISSN:0169-555xISSN:1872-695