CONFIDENTIAL Rangitāiki River Technical Background and Response to Edgecumbe April 2017 Flood
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CONFIDENTIAL Rangitāiki River Technical Background and Response to Edgecumbe April 2017 Flood Documentation for Independent Review 2 June 2017 Version 1.0 for release to Review Panel Bay of Plenty Regional Council 5 Quay Street PO Box 364 Whakatāne 3158 NEW ZEALAND Prepared by Bay of Plenty Regional Council Cover Photo: Edgecumbe Floodwall 8 June 2007 Photographer: Tony Dunlop Acknowledgements The Bay of Plenty Regional Council would like to pay tribute to the residents of Edgecumbe particularly those who have lost homes and property and had their lives disrupted by the flood of April 2017. We also pay tribute to all the volunteers involved in the flood response and subsequent clean-up. The Council provides this report and associated documents to assist with the independent review to be undertaken in accordance with the Terms of Reference dated 22 May 2017. The Terms of Reference provide that the purpose of the review is to understand the circumstances that led to the breach of the Rangitāiki River stopbank at College Road, Edgecumbe, and the resulting flooding through the town on 6 April 2017. BOPRC acknowledges the huge efforts of Ken Tarboton and Debbie Fransen for their dedication in compiling this report and identification of the associated documents of key relevance for the work of the independent review panel. USE OF REPORT AND DOCUMENTS This report and documents provided by the Council to the panel are for the sole purpose of their independent review. The report and documents may be subject to confidentiality, commercial sensitivity, legal professional privilege, and privacy obligations or able to be withheld from production under the Local Government Official Information & Meetings Act 1987 or otherwise. Provision of the report and documents does not constitute a waiver by the Council of its rights to otherwise refuse production of the report and documents. The panel members, including their advisors, will not disclose the report or documents to any third party without the Council’s prior written consent. Upon conclusion of the panel’s engagement, all copies of this report or documents must be returned to the Council or destroyed. Rangitāiki River Technical Background and Response to Edgecumbe April 2017 Flood i Contents Acknowledgements i USE OF REPORT AND DOCUMENTS i 1 Introduction 1 2 Overview of the Rangitāiki-Tarawera Catchments 3 2.1 Geography and land use 3 2.2 Topography and geology 4 2.3 Hydrology 4 2.4 Cultural values 6 3 Significant Events and Development of the Rangitāiki- Tarawera Floodplains 7 3.1 Flood and Event Timeline 7 3.2 Early flooding and drainage 9 3.3 Rangitāiki-Tarawera Rivers Scheme 11 3.4 1987 Edgecumbe Earthquake 11 3.5 1998 Flood Event 12 3.6 2004 Flood Event 12 3.7 2008 to 2016 Floods 14 4 Geotechnical Investigations and Works 15 4.1 Stopbank design and construction 15 4.2 General Geotechnical Investigations 16 4.2.1 Following 1987 earthquake 16 4.2.2 Following 1998 flood 16 4.2.3 Following July 2004 flood 17 4.3 Edgecumbe Floodwall, College Road 17 Rangitāiki River Technical Background and Response to Edgecumbe April 2017 Flood iii 4.3.1 Original floodwall construction 17 4.3.2 Post-earthquake new wall in 1993 (1.4m high) 18 4.3.3 Post 1998 flood event works 19 4.3.4 Post July 2004 flood remedial works 19 4.3.5 April 2017 breach repair (temporary) works: 23 5 Hydraulic and Hydrologic Modelling 25 5.1 Design flows 25 5.1.1 Design flow and sea level assumptions 25 5.2 Cross section analysis 26 5.3 Hydraulic modelling 26 5.4 Summary of recent Hydraulic Modelling for Rangitāiki Catchment 27 5.4.1 Hydraulic capacity review of the Lower Rangitāiki River and the Reids Floodway - Opus 2011 27 5.4.2 Peer review of the Opus model by Philip Wallace, 2010. 27 5.4.3 Rangitāiki River Modelling Report, URS, 2012 28 5.4.4 Upper Rangitāiki Flood Forecasting Model Operational Manual, EWaters, 2012. 28 6 Flood Mitigation Works 29 6.1 Summary of Mitigation Works and Funding Application. 29 6.2 Resource Consent Application for Mitigation Works 29 6.3 Funding application 29 6.4 Geotechnical strengthening works 30 6.5 Rangitāiki Floodway widening works 31 6.6 Spillway Options 33 7 Flood Management 35 7.1 Operational flood management 35 7.1.1 Flood management training and development 35 iv Rangitāiki River Technical Background and Response to Edgecumbe April 2017 Flood 7.2 Hydropower dam operations 36 7.3 Matahina Dam 36 7.3.1 Matahina general background 37 7.3.2 Matahina consenting process 37 7.3.3 Matahina Dam flood operations 37 7.4 Modelling used for operational flood management 38 8 Flood Risk Planning 39 8.1 Flood risk assessment of the Rangitāiki Plains 39 8.2 Rangitāiki Tarawera Flood Plain Management Strategy 39 8.3 Regional Flood Risk Management Framework 40 8.4 River Scheme Sustainability 40 8.5 Infrastructure Strategy 40 9 Asset Management 41 9.1 Asset management planning 41 9.2 Rivers and Drainage AMP – excerpts for Rangitāiki-Tarawera 42 9.2.1 Design Levels 43 9.2.2 Asset condition, capacity and reliability 44 9.2.3 Asset value 45 9.2.4 Capital works 45 9.3 Operational Asset Management 47 9.3.1 Rangitāiki-Tarawera River Scheme Liaison Group Meetings 47 10 Communication and Decision-making 49 10.1 Long Term Plan direction and funding 49 10.2 Council papers 50 10.3 Other Communication 50 11 Flood Event Response 51 Rangitāiki River Technical Background and Response to Edgecumbe April 2017 Flood v 11.1 Event Management 51 11.2 Flood Forecasting (including Met Service warnings) 51 11.3 Flood Logs & Trustpower Communication 53 11.4 Key Flood Management Decisions 53 11.5 Inspections 56 11.6 Event photos 56 12 Post event investigations and analysis 57 12.1 Matahina Dam operations 57 12.2 Reids Canal Spillway Operations 57 12.3 College Road stopbank breach investigation 59 12.4 Rangitāiki River @ Te Teko Rating Curve 59 13 References 61 Appendix 1 – Map Archive 73 Table A1.1 Rangitāiki (R) tab content sample. 73 Table A1.2 Rangitāiki (R) tab content sample. 73 Table A1.3 Key Groups of plans developed for initial scheme construction and as a result of the earthquake and major floods. 73 Appendix 2 – Flood Management Team Structure 75 Appendix 3 – Flood Log Summary 3-6 April 77 Table A3.1 Summary of Flood logs from 3-6 April 2017 77 Table A3.2 Notes from Mark Townsend. Conference Call with TrustPower on 5 April 2017, 11:30 am. 79 vi Rangitāiki River Technical Background and Response to Edgecumbe April 2017 Flood Tables Table 1 Predicted peak flows in the Rangitāiki and Whirinaki Rivers (Britton, 2008) 6 Table 2 Hydrologic parameters based on a calibrated model of the July 2004 Storm (Astudillo,2011) 6 Table 3 Flood event and development timeline (floods shaded blue, earthquake shaded green) 8 Table 4 Ranked historical flood discharge for Whirinaki and Rangitāiki Rivers (FWM. Thompson, 2016). 13 Table 5 Summary of berm and rockwork completed from 2005 to 2012 in the vicinity of the Edgecumbe Floodwall (Flood repair report to RTLG 2012). 23 Table 6 Design flows and sea levels used in Rangitāiki River flood modelling (Wallace, 2011). 26 Table 7 Comparison of Spillway options (Smith et al., 2014). 33 Table 8 Rangitāiki-Tarawera Rivers Scheme Stopbank and Rangitāiki drainage scheme design standards (Section 4.5, AMP 2015). 44 Table 9 Rangitāiki-Tarawera Rivers Scheme Asset Condition (AMP, 2015. p145). 45 Table 10 Rangitāiki-Tarawera Rivers Scheme Asset value (AMP, 2015. Table 48 p144). 45 Table 11 Projected capital expenditure for Rangitāiki-Tarawera Rivers Scheme (AMP, 2015. Table 51 p 147). 46 Table 12 Capital and Replacement Projects for 2014/2015 – 2024/2025 (AMP 2015. Table 68 p 176). 46 Table 13 Roles for ex-cyclone Debbie event. 51 Rangitāiki River Technical Background and Response to Edgecumbe April 2017 Flood vii Figures Figure 1 Rangitāiki River Catchment (RRF, 2015. p13). 3 Figure 2 Profile of the Rangitāiki River (RRF, 2015. p30). 4 Figure 3 Rangitāiki, Tarawera and Whakatāne River catchments and Rangitāiki Plains (Wallace, 2013) 4 Figure 4 Rangitāiki Plains Historical Sketch showing drainage pattern c 1866/67 (BOPRC Maps and Plans Archive, R722).) 5 Figure 5 Flood peak history of the Rangitāiki River at Te Teko from 1944 to 2017 (from Te Teko gauging station, plotted by Fransen 2017). 2017 Peak flow has been recalibrated to 741m3/s (Ellery, 2017) 7 Figure 6 Stopbank breach at Reynolds Bend, Rangitāiki River in 1962 (river flow direction is from right to left). (from BOPCC, 1985 p14 in Britton, 2008 p16). 10 Figure 7 Stopbank breach at Sullivans Bend, Rangitāiki River July 2004. (Britton 2008) 13 Figure 8 Extent of July 2004 floods in Rangitāiki Plains (Britton, 2008) Note: purple silty water, blue surface water. 14 Figure 9 Typical cross-section through Rangitāiki River, stopbanks and floodplain (Wallace, 2013) 16 Figure 10 Location of Geotechnical Investigations following 1998 flood (Dennison, 2000). 16 Figure 11 Typical cross-section of 600mm high wall copied from plan R450/12 (BOPCC, 1973b) 18 Figure 12 Typical cross-section of 1400mm high wall copied from plan R674(sheet 4 of 4) (BOPCC, 1973b) 18 Figure 13 Crib wall design for College Road (Dennison, 2000. Opus). 19 Figure 14 Rangitāiki River at Edgecumbe (north of SH2) showing river distances (Source: BOPRC GIS) 20 Figure 15 Rangitāiki River Geotechnical Remedial Works, as at 29 February 2008 21 Figure 16 Rangitāiki River at Edgecumbe identifying geotechnical work sites during period 2004-2014 (Source: plan M1804, BOPRC, 2014c).