Back-analysis study of selected Norwegian debris flow and debris avalanche events A comparison of DAN3D and GeoClaw runout models Graeme Robert Carey Master’s Thesis in Geoscience Discipline: Geohazards Department of Geoscience Faculty of Mathematics and Natural Sciences UNIVERSITY OF OSLO June 2018 ii Back-analysis study of selected Norwegian debris flow and debris avalanche events A comparison of DAN3D and GeoClaw runout models Graeme Robert Carey Master’s Thesis in Geoscience Discipline: Geohazards Department of Geoscience Det Matematisk-naturvitenskapelige Fakultet Universitetet i Oslo June 2018 iii iv © Graeme Carey, 2018 Supervisors: José Mauricio Cepeda (NGI), Anders Solheim (NGI/UIO) Back-analysis study of selected Norwegian Debris Flow and Avalanche Events: a comparison of DAN3D and GeoClaw runout models http://www.duo.uio.no/ Print: Reprosentralen, Universitetet i Oslo Cover photo: Southern Oldedalen, seen from the initiation zone of Oldedalen 1. Graeme Carey, 2017. v Abstract Debris flows and debris avalanches represent a large threat to society in Norway. The intensity and frequency of these events is expected to increase over the course of the next 50 years due to changing precipitation patterns related to global climate change. Models are continually being developed and tested to better understand and characterise these events. An important part of creating regional and local-scale hazard maps is understanding the potential runout distance and velocity that can be achieved by these events. This thesis provides a detailed study of four landslide events in western Norway (two debris flows and two debris avalanches) additionally, it compares two software packages used for landslide back-analysis. The work presented is part of the Klima2050 research initiative. Field visits were conducted at each site in order to develop a better understanding of the event geometry and take soil samples to construct grain size distribution curves for each event. These grain size distributions were used to estimate the static friction of each soil sample. Landslide back-analysis was conducted using DAN3D to determine rheological parameters for each event. Simulations were also conducted in GeoClaw, to compare it with DAN3D and determine its suitability for the runout modelling of debris flow events. Dynamic friction angles calibrated in the models were compared to the static friction angles obtained from the grain size distributions. Simulation results agree with field observations of the debris flow and debris avalanche events. DAN3D was found to underestimate the runout of the landslide events, but simulations were a good fit with the path geometries. GeoClaw overestimated the material mobility and did not include material entrainment. Therefore, DAN3D is currently the more viable of the two programs for accurately modelling and characterising debris flow and debris avalanche events. vi Acknowledgments I owe thanks to a number of people for giving me advice and aid throughout the course of this thesis. First, thank you to my supervisors Anders Solheim and José Cepeda for their help and support. Your advice and experience has been invaluable in helping me to complete this project, and I have learned so much from both of you over the last few years. I would like to thank Mufak Said Naoroz from the University of Oslo Department of Geosciences for his help in setting up the laboratory experiments and completing the grain size analysis curves, and Zhongqiang Liu from NGI for his technical assistance and help working with GeoClaw and the NGI servers. Without your help I would have spent many frustrating hours trying to trouble shoot simulations in GeoClaw, and likely would never have gotten them running. I would also like to thank Krister Kristensen (NGI) for the assistance and advice during the field work in Stryn, as well as helping me to procure the helicopter images of both Oldedalen events. I cannot stress enough how helpful having high quality images from multiple angles taken immediately after the events occurred was in modelling and characterising the sites. Thanks to Kasper Skjeggestad, Simon Anfinnsen, Daniel Lupp, and Craig Christensen for their help writing Matlab codes, proofreading, and giving me writing tips throughout the last two semesters. Finally, thank you to all my friends in Norway who helped me settle into life in a new country, and helped me as I tried to learn a new language; even if some of you took a perverse pleasure in confusing me with dialects and writing in nynorsk. Additionally, a special thankyou to everyone in room 214 for the table tennis matches and Friday cakes. Graeme R. Carey 31.05.2018 vii viii Table of Contents 1 Introduction ........................................................................................................................ 1 2 Theory ................................................................................................................................ 3 2.1 Mass Movement .......................................................................................................... 3 2.2 Debris flows and avalanches ....................................................................................... 4 2.2.1 Behaviour ............................................................................................................. 6 2.2.2 Causes and Triggers ............................................................................................. 8 2.2.3 Impacts ............................................................................................................... 10 2.3 Selected Runout Models ............................................................................................ 11 2.3.1 DAN3D .............................................................................................................. 11 2.3.2 GeoClaw ............................................................................................................. 13 2.3.3 Rheology/Parameters ......................................................................................... 14 2.4 Geological and Climatological Setting ...................................................................... 15 2.4.1 Geological Setting .............................................................................................. 15 2.4.2 Climatological Setting ........................................................................................ 17 2.5 Risk and Hazard Assessment ..................................................................................... 19 3 Methods ............................................................................................................................ 22 3.1 Field Work ................................................................................................................. 22 3.2 Grain size analysis ..................................................................................................... 23 3.2.1 Sample preparation and sieving ......................................................................... 24 3.2.2 Coulter test ......................................................................................................... 25 3.2.3 Appending large clasts ....................................................................................... 25 3.2.4 Grain size distribution curves ............................................................................. 25 3.3 Runout Simulations ................................................................................................... 26 3.3.1 DAN3D – Numerical Parameters ....................................................................... 26 3.3.2 DAN3D .............................................................................................................. 26 3.3.3 GeoClaw ............................................................................................................. 28 4 Site Descriptions .............................................................................................................. 29 4.1 Nesbyen Arnegårdslie ................................................................................................ 29 4.1.1 Terrain ................................................................................................................ 30 4.1.2 Bedrock and Soil Characteristics ....................................................................... 30 4.1.3 Release Area ....................................................................................................... 31 4.1.4 Transport Zone and Deposition .......................................................................... 32 ix 4.2 Oldedalen 1 ................................................................................................................ 34 4.2.1 Terrain ................................................................................................................ 35 4.2.2 Bedrock and Soil Characteristics ....................................................................... 36 4.2.3 Release Area ....................................................................................................... 37 4.2.4 Transport zone and Deposition........................................................................... 38 4.3 Oldedalen 2 ................................................................................................................ 40 4.3.1 Terrain ................................................................................................................ 41