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Landslide Risks in the Göta River Valley in a Changing Climate

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Landslide Risks in the Göta River Valley in a Changing Climate Landslide risks in the Göta River valley in a changing climate Final report Part 2 - Mapping GÄU The Göta River investigation 2009 - 2011 Linköping 2012 The Göta River investigation Swedish Geotechnical Institute (SGI) Final report, Part 2 SE-581 93 Linköping, Sweden Order Information service, SGI Tel: +46 13 201804 Fax: +46 13 201914 E-mail: [email protected] Download the report on our website: www.swedgeo.se Photos on the cover © SGI Landslide risks in the Göta River valley in a changing climate Final report Part 2 - Mapping Linköping 2012 4 Landslide risks in the Göta älv valley in a changing climate 5 Preface In 2008, the Swedish Government commissioned the Swedish Geotechnical Institute (SGI) to con- duct a mapping of the risks for landslides along the entire river Göta älv (hereinafter called the Gö- ta River) - risks resulting from the increased flow in the river that would be brought about by cli- mate change (M2008/4694/A). The investigation has been conducted during the period 2009-2011. The date of the final report has, following a government decision (17/11/2011), been postponed until 30 March 2012. The assignment has involved a comprehensive risk analysis incorporating calculations of the prob- ability of landslides and evaluation of the consequences that could arise from such incidents. By identifying the various areas at risk, an assessment has been made of locations where geotechnical stabilising measures may be necessary. An overall cost assessment of the geotechnical aspects of the stabilising measures has been conducted in the areas with a high landslide risk. Furthermore, an overall assessment of the geotechnical preconditions for increased flow in the Göta River is also presented. The investigation has primarily been conducted by SGI employees. The work has been led by SGI's management group, under the leadership of the Director General, Birgitta Boström. The work has been organised into one main assignment for the project management and into a large number of sub-assignments, as far as method development and investigation are concerned. SGI has utilised the support of a number of agencies and research institutions, including the Swedish Meteorological and Hydrological Institute (SMHI), the Geological Survey of Sweden (SGU), Chalmers University of Technology, Lund University, the University of Stuttgart, the Norwegian Geotechnical Institute (NGI), Vattenfall, the Swedish Maritime Administration and the Swedish Transport Administration. All municipalities within the Göta River valley and the County Admin- istrative Board of Västra Götaland have also participated at various stages of the project. Finally, SGI has engaged a large number of consultants, primarily from the Göteborg region, as extra re- sources in the implementation of the investigative work. The results and conclusions of the investigation are presented in a final report, Landslide risks in the Göta River valley in a changing climate. The report consists of three parts: Final report, Part 1 – Societal Consequences, which comprises a summary of the assign- ment, landslide risks and the consequences for society, the costs of measures and the pro- posals of the investigation with regard to future activities. Part 1 is aimed primarily at those who require an overall description of the landslide risks that exist in the valley, how these may affect the local community and the measures that need to be taken. Final report, Part 2 – Mapping, which comprises a description of the investigation's methodology, inventories, field and laboratory investigations, calculations and analyses. The target group for Part 2 is those who wish to delve deeper into the investigation and acquire more detailed facts regarding the various conditions in the valley, as a basis for planning and adapting to climate change. Final report, Part 3 – Maps, which comprises an account of the landslide risks for various parts of the Göta River, in map form. Part 3 describes where along the river the landslide risks can be found and the areas that would be affected. The maps also contain a classifica- tion of the climatic impact along the river. In addition to the final report, the detailed work involved with the taking of inventories, method development and analyses has also been described in 34 sub-reports that were submitted to the government on 21/12/2011. The reports are listed in the Appendix and are available via SGI's website: www.swedgeo.se Final report, part 2 - Mapping 6 Final report, Part 2 has been edited by Karin Lundström and Bengt Rydell. Text has been submit- ted by Yvonne Andersson-Sköld, Per-Evert Bengtsson, Charlotte Cederbom, Stefan Falemo, Gun- nel Göransson, Bo Lind, Karin Lundström, Hjördis Löfroth, Håkan Persson, Bengt Rydell, Hanna Tobiasson-Blomén, Marius Tremblay, Helen Åhnberg and Mats Öberg. The checking of technical details has been conducted by Rolf Larsson. Elin Sjöstedt has been responsible for layout and proofreading has been conducted by Per Samuelson and Anders Salomonson. This is a translation from the Swedish original and the SGI may not be claimed responsible for any misunderstanding or error that may occur from the translation. Linköping, March 2012 Bo Lind Acting Director General Landslide risks in the Göta älv valley in a changing climate 7 Table of contents The Göta River investigation - in brief ....................................................... 9 1 The assignment ...................................................................................... 14 1.1 The Government's commission ........................................................................ 14 1.2 Background ......................................................................................................... 14 1.3 The Göta River and the local community ........................................................ 15 1.4 Landslides in the Göta älv valley ...................................................................... 17 2 How the investigation has been conducted ......................................... 20 2.1 Scope and limitations ........................................................................................ 20 2.2 Organisation ....................................................................................................... 21 2.3 The GIS platform and GIS applications ............................................................ 25 3 The climate of today and in the future in the Göta River valley ......... 28 3.1 The climate of today ........................................................................................... 28 3.2 Climate changes ................................................................................................. 30 3.3 Sea levels today and in the climate of the future ............................................ 32 4 Geology and landforms .......................................................................... 34 4.1 Geological conditions ........................................................................................ 34 4.2 Topography and landforms ............................................................................... 41 4.3 Terrain model ...................................................................................................... 45 5 Geotechnics ............................................................................................ 46 5.1 The field investigations that were conducted ................................................. 46 5.2 The laboratory investigations that were conducted ....................................... 48 5.3 Methodology for the mapping of quick clay .................................................... 48 5.4 Geotechnical conditions .................................................................................... 50 6 Surface and groundwater conditions in the climate of today and in the future ...................................................................................................... 60 6.1 Methodology ....................................................................................................... 60 6.2 Flows in the Göta River ..................................................................................... 60 6.3 Water discharge in the Göta River's tributaries .............................................. 64 6.4 Water levels in the Göta River ........................................................................... 65 6.5 Groundwater conditions in soil layers along the Göta River ........................ 66 7 Erosion .................................................................................................... 73 7.1 How the investigation was organised .............................................................. 73 7.2 Erosion processes in the Göta River ............................................................... 74 7.3 Investigations and inventories .......................................................................... 76 7.4 Changes to the bottom levels ........................................................................... 80 7.5 Hydrodynamic calculations ............................................................................... 83 7.6 The effect of marine traffic on erosion ............................................................. 86 7.7 Sediment transport............................................................................................. 88 7.8 Erosion conditions in the climate of today ...................................................... 90 7.9 Erosion conditions in the climate
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