Natural Hazard Assessment for the Township of Franz Josef, Westland District Natural Hazard Assessment for the Township of Franz
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Natural Hazard Assessment for the Township of Franz Josef, Westland District R.M. Langridge J.D. Howarth R. Buxton W.F. Ries GNS Science Consultancy Report 2016/33 July 2016 DISCLAIMER This report has been prepared by the Institute of Geological and Nuclear Sciences Limited (GNS Science) exclusively for and under contract to the Envirolink Fund/West Coast Regional Council. Unless otherwise agreed in writing by GNS Science, GNS Science accepts no responsibility for any use of or reliance on any contents of this report by any person other than the Envirolink Fund/West Coast Regional Council and shall not be liable to any person other than the Envirolink Fund/West Coast Regional Council, on any ground, for any loss, damage or expense arising from such use or reliance. Use of Data: Date that GNS Science can use associated data: July 2016 BIBLIOGRAPHIC REFERENCE Langridge, R.M.; Howarth, J.D.; Buxton, R., Ries, W.F. 2016. A Natural Hazard Assessment for the Township of Franz Josef, Westland District, GNS Science Consultancy Report 2016/33. 61 p. Project Number 430W4150 Confidential 2016 CONTENTS EXECUTIVE SUMMARY ...................................................................................................... IV 1.0 INTRODUCTION ........................................................................................................ 1 1.1 SCOPE OF WORK ............................................................................................... 2 1.2 PROJECT DESIGN .............................................................................................. 3 2.0 SETTING ....................................................................................................................5 2.1 FRANZ JOSEF TOWNSHIP ................................................................................... 5 2.2 LATE QUATERNARY GEOLOGY OF THE FRANZ JOSEF AREA .................................. 9 2.2.1 1:100,000 Scale Geology ................................................................................... 9 2.2.2 1:10,000 Scale Geology ...................................................................................10 2.2.3 Estimates of Surface Ages for the High and Town Terraces ...........................12 3.0 NATURAL HAZARDSCAPE .................................................................................... 15 3.1 DIRECT SEISMIC-RELATED FAULT HAZARDS ..................................................... 15 3.1.1 Ground Surface Rupture Hazard ......................................................................15 3.1.2 Frequency and Expected Levels of Ground Surface Displacement ................18 3.1.3 Seismic Shaking ...............................................................................................19 3.1.4 Liquefaction and Lateral Spreading .................................................................22 3.1.5 Liquefaction Hazard – Franz Josef Area ..........................................................24 3.1.6 Lateral Spreading Hazard – Franz Josef Area .................................................26 3.2 WATER-DRIVEN NATURAL HAZARDS ................................................................. 27 3.2.1 Waiho River Flooding .......................................................................................27 3.2.2 Alluviation in Rivers ..........................................................................................29 3.2.3 Alluvial Fans .....................................................................................................30 3.3 GRAVITY-DRIVEN NATURAL HAZARDS ............................................................... 33 3.3.1 Landslides ........................................................................................................33 3.3.2 Non-Seismic Landsliding ..................................................................................33 3.3.3 Seismic-Induced Landsliding ............................................................................35 3.3.4 Rock Avalanche................................................................................................36 3.3.5 Landslide Dams and Outburst Floods ..............................................................38 3.4 MULTI-HAZARD SCENARIO – THE ALPINE FAULT EARTHQUAKE .......................... 39 4.0 ASSESSMENT OF NATURAL HAZARDS ............................................................... 43 4.1 DIRECT CO-SEISMIC HAZARDS ......................................................................... 44 4.1.1 Surface Faulting and Deformation....................................................................44 4.1.2 Strong Ground Motions ....................................................................................45 4.1.3 Liquefaction and Lateral Spreading .................................................................46 4.2 WATER-DRIVEN HAZARDS ............................................................................... 46 4.2.1 Waiho River Flooding .......................................................................................46 4.2.2 Alluviation .........................................................................................................47 GNS Science Consultancy Report 2016/33 i Confidential 2016 4.3 GRAVITY-DRIVEN HAZARDS ............................................................................. 48 4.3.1 Non-Seismic Landslide Hazard ........................................................................48 4.3.2 Earthquake-Induced Landslide Hazard ............................................................49 4.3.3 Rock Avalanche................................................................................................49 5.0 SUMMARY ............................................................................................................... 51 6.0 DISCUSSION AND RECOMMENDATIONS ............................................................. 55 7.0 ACKNOWLEDGEMENTS ......................................................................................... 57 8.0 REFERENCES ......................................................................................................... 57 FIGURES Figure 1.1 Active tectonic setting of New Zealand. ........................................................................................ 1 Figure 1.2 Digital elevation and rainfall gradient of the central South Island ................................................. 2 Figure 2.1 Location map of the wider Franz Josef area. ................................................................................ 5 Figure 2.2 Simplified geological map at scale 1:100,000 ............................................................................... 7 Figure 2.3 Geologic and geomorphic map produced at scale c. 1:12,000 developed using, and extending from, the underlying LiDAR DEM. .............................................................................. 11 Figure 2.4 A south to north profile across the High terrace from upstream of Franz Josef, running into the town. .............................................................................................................................. 12 Figure 3.1 Schematic diagram of the dextral- reverse Alpine Fault and its Fault Avoidance Zone .............. 16 Figure 3.2 Updated Fault Avoidance Zones (purple polygonal shapes) for the area between Docherty Creek and Potters Creek. ............................................................................................ 17 Figure 3.3 Modified Mercalli Intensity maps for the central South Island highlighting various earthquake sources .................................................................................................................... 20 Figure 3.4 A 10% in 250 year (2500 year) deaggregation plot for the town of Franz Josef assuming Class D (deep) soils. .................................................................................................................. 21 Figure 3.5 Areas that may be susceptible to liquefaction (LQ) and/or lateral spreading (LS) in the wider Franz Josef area. ............................................................................................................. 25 Figure 3.6 A topographic profile drawn across the Waiho fan from the ‘Lavender’ lobe in the SW to the edge of the Tartare fan, NE of Franz Josef town using LiDAR data. .................................... 27 Figure 3.7 Flooding scenarios for the Waiho River for four time periods based on modelling undertaken by Land River Sea Ltd. ............................................................................................ 28 Figure 3.8 A 100-year flood scenario for the Waiho River following aggradation of the river bed by 4 metres at a rate of up to 0.2 m per year ..................................................................................... 30 Figure 3.9 Geomorphic map of Franz Josef town. ....................................................................................... 34 Figure 3.10 Co-seismic landslide susceptibility map for an Mw 8 Alpine Fault earthquake scenario .............. 35 Figure 3.11 Large to giant landslides or rock avalanches along the Alpine Fault Zone ................................. 37 Figure 3.12 Flow chart for a multi-hazard event that follows rupture of the alpine Fault in a Mw 8 earthquake. ................................................................................................................................ 40 Figure 4.1 Updated Fault Avoidance Zones for the area between the S.H. 6 bridge (black line) and Tartare