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Te Puru Stream flood protection scheme - service level review (Supplementary report - July 2020)

TR 2020/18
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Report: TR 2020/18

Author: Duncan Grant

Abstract

A service level review of the flood protection assets on the Te Puru Stream was completed in October 2019 (Grant, 2019). The process included a reassessment of catchment hydrology and design flows, a complete rebuild of hydraulic models based on available topographic datasets, and a comparison of revised flood profiles against surveyed asset crest levels. The review indicated the scheme could convey the design flow but shortfalls in freeboard were identified in the lower scheme, possibly associated with sediment aggradation near the mouth. Recommendations of the review included re-survey of the channel to compare with past datasets, reassessment of the flood protection assets, and determination of appropriate bed levels in the lower scheme to maintain freeboard.

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Te Puru Stream flood protection scheme - service level review (Supplementary report - July 2020) [PDF, 2.2 MB]

Contents
Abstract v
1 Introduction 6
1.1 Purpose 6
2 Flood protection scheme 6
3 Survey 8
3.1 Datum and offsets 8
3.2 Ground survey 2004, 2014 and 2002 8
3.3 LIDAR 2013 9
4 Hydraulics 10
4.1 Revised MIKE11 model July 2020 10
4.1.1 MIKE11 model development 10
4.1.2 MIKE model results - 2020 simulation 11
4.1.3 MIKE11 model summary 16
5 Service level review of flood protection assets 18
5.1 Suggested change in service level for right bank 'floodwall extension' 18
6 Conclusions 27
7 Recommendations 28
References 29
Appendix A - Comparison of ground survey cross-section (2014 - local datum) and LIDAR DTM slices (2012 - AVD-46+0.13 i.e. local datum) 30
Appendix B - Comparison of 2004, 2014 and 2020 ground survey cross-sections 47
Appendix C - Conquest service level data 63