Methods for rockfall risk assessment and estimation of runout zones: A case study in Gothenburg, SW Sweden
(2020) GEOR02 20192Department of Geology
- Abstract
- Rockfalls occur around Sweden every year and the country lacks a national risk evaluation and an adequate regulatory framework for construction related to this natural hazard. The aim of this study is to address this problem by mapping areas under possible threat of rockfalls, considering two fundamental aspects: i) identification of the source areas and ii) estimation of the runout zones. The study was performed in the northeastern part of the Gothenburg municipality, particularly focusing on Fjällbo park, a popular climbing area where large talus slopes under the cliffs show evidence of both historic and recent rockfalls. The most recent event occurred in 2017. Potential rockfall source areas were outlined using a statistical method... (More)
- Rockfalls occur around Sweden every year and the country lacks a national risk evaluation and an adequate regulatory framework for construction related to this natural hazard. The aim of this study is to address this problem by mapping areas under possible threat of rockfalls, considering two fundamental aspects: i) identification of the source areas and ii) estimation of the runout zones. The study was performed in the northeastern part of the Gothenburg municipality, particularly focusing on Fjällbo park, a popular climbing area where large talus slopes under the cliffs show evidence of both historic and recent rockfalls. The most recent event occurred in 2017. Potential rockfall source areas were outlined using a statistical method called Slope Angle Distribution (SAD), which combines information about the geology and topography of an area with the slope angle values extracted from a Digital Elevation Model (DEM). Runout zones were simulated using two programs: CONEFALL and RockfyFor3D, process-based software that use a DEM as a fundamental part of the analyses. CONEFALL uses the energy line method to estimate runout zones, whereas RockyFor3D considers different characteristics of the blocks, slopes, as well as protective effects from the forest density and tree sizes.
According to the SAD method, all angles above 40° - 42° are considered potential rockfall sources in the study area. CONEFALL generates rather conservative models and the outcomes are dependent on the topography and the height of the cliffs. Moreover, the lateral extent of the runout zones is overestimated by the software but can be adjusted by constraining its aperture angle. On the other hand, RockyFor3D generates more realistic outcomes and shows that the block shape affects the lateral extent of runout zones and block mass controls the energy dissipation of the blocks. Likewise, it shows that the bouncing behavior of the blocks on the surface is mostly controlled by the slope gradient and the coefficient of restitution, which is dependent on the type of soil or rock, and by the obstacles encountered on the way (their distribution and their sizes). Lastly, these simulations indicate that forests act as protective agents, as they may stop the falling blocks; however, the protection efficacy depends mainly on the density of the forest. The 2017 rockfall occurred in Fjällbo was included in the simulations performed using CONEFALL and RockyFor3D as a verification point of the applicability and accuracy of the two software models.
The SAD methodology for potential rockfall source detection, as well as the runout zone estimations obtained with CONEFALL and RockyFor3D models may serve as a foundation for further and more detailed risk assessment. These methods, however, are sensitive to topography, morphology and geology of the area, and, therefore, it is paramount to perform verifications of the study area with fieldwork and/or high-resolution remote sensing imagery. Depending on the topographical and geological information available, these methods can be used at both local and regional scales. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9019226
- author
- Agudelo Motta, Laura Catalina LU
- supervisor
- organization
- course
- GEOR02 20192
- year
- 2020
- type
- H2 - Master's Degree (Two Years)
- subject
- keywords
- Rockfall hazard, rockfall simulation, Gothenburg, Fjällbo, runout zones
- funder
- Svenska Institutet
- language
- English
- additional info
- External supervisor: Johan Berglund, Statens geotekniska institut
- id
- 9019226
- date added to LUP
- 2020-06-18 10:44:35
- date last changed
- 2023-06-18 03:41:55
@misc{9019226,
abstract = {{Rockfalls occur around Sweden every year and the country lacks a national risk evaluation and an adequate regulatory framework for construction related to this natural hazard. The aim of this study is to address this problem by mapping areas under possible threat of rockfalls, considering two fundamental aspects: i) identification of the source areas and ii) estimation of the runout zones. The study was performed in the northeastern part of the Gothenburg municipality, particularly focusing on Fjällbo park, a popular climbing area where large talus slopes under the cliffs show evidence of both historic and recent rockfalls. The most recent event occurred in 2017. Potential rockfall source areas were outlined using a statistical method called Slope Angle Distribution (SAD), which combines information about the geology and topography of an area with the slope angle values extracted from a Digital Elevation Model (DEM). Runout zones were simulated using two programs: CONEFALL and RockfyFor3D, process-based software that use a DEM as a fundamental part of the analyses. CONEFALL uses the energy line method to estimate runout zones, whereas RockyFor3D considers different characteristics of the blocks, slopes, as well as protective effects from the forest density and tree sizes.
According to the SAD method, all angles above 40° - 42° are considered potential rockfall sources in the study area. CONEFALL generates rather conservative models and the outcomes are dependent on the topography and the height of the cliffs. Moreover, the lateral extent of the runout zones is overestimated by the software but can be adjusted by constraining its aperture angle. On the other hand, RockyFor3D generates more realistic outcomes and shows that the block shape affects the lateral extent of runout zones and block mass controls the energy dissipation of the blocks. Likewise, it shows that the bouncing behavior of the blocks on the surface is mostly controlled by the slope gradient and the coefficient of restitution, which is dependent on the type of soil or rock, and by the obstacles encountered on the way (their distribution and their sizes). Lastly, these simulations indicate that forests act as protective agents, as they may stop the falling blocks; however, the protection efficacy depends mainly on the density of the forest. The 2017 rockfall occurred in Fjällbo was included in the simulations performed using CONEFALL and RockyFor3D as a verification point of the applicability and accuracy of the two software models.
The SAD methodology for potential rockfall source detection, as well as the runout zone estimations obtained with CONEFALL and RockyFor3D models may serve as a foundation for further and more detailed risk assessment. These methods, however, are sensitive to topography, morphology and geology of the area, and, therefore, it is paramount to perform verifications of the study area with fieldwork and/or high-resolution remote sensing imagery. Depending on the topographical and geological information available, these methods can be used at both local and regional scales.}},
author = {{Agudelo Motta, Laura Catalina}},
language = {{eng}},
note = {{Student Paper}},
title = {{Methods for rockfall risk assessment and estimation of runout zones: A case study in Gothenburg, SW Sweden}},
year = {{2020}},
}