Tararu flood protection scheme design report

TR 2013/46
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Report: TR 2013/46

Author: Megan Wood (Wainui Consulting Limited)

About this report

The purpose of this Design Report is to provide a summary of the works that have been undertaken at Tararu to reduce the flood hazard from the Tararu Stream, including the rationale behind the scheme development, the agreed levels of service, the design details, as built information, the operation and maintenance requirements of the scheme, the residual flood risk and the scheme review requirements.

The Design Report includes the following sections:

  • Catchment overview
  • Hydrological assessment
  • Hydraulic model development
  • Flood protection scheme
  • Agreed levels of service
  • Operation and maintenance
  • Flood hazard assessment
  • Residual flood risk
  • Planning controls, and
  • Scheme review.

Read or download the report

Tararu flood protection scheme design report [PDF, 6 MB]

Contents
  Executive summary vii 
 1 Introduction 1 
 1.1 Background 1 
 1.2 Scope of report 1
 2 Catchment overview 3 
 2.1 Catchment description 3
 2.2 Tararu Stream 4
 2.2.1 General 4 
 2.2.2 Pre-scheme condition of Tararu Stream 5 
 2.3 Flooding issues  6
 3 Hydrological assessment 9 
 3.1 Technical information  9
 3.2 Catchment characteristics 10 
 3.3 Rainfall  10
 3.4 Flow estimates  12
 3.5 Hydrograph 13 
 4 Hydraulic model development  14
 4.1 Introduction  14
4.2  Model build  14
 4.3 Model inputs  14
 4.3.1 Model datum  14
4.3.2  Channel cross section data  14
 4.3.3 Upper boundary condition  14
 4.3.4 Lower boundary condition  14
 4.3.5 Roughness  15
 4.3.6 Model location  15
 4.4 Bridge representation 15 
 4.4.1 Background  15
 4.4.2 Model set up 15 
 4.4.3 Description of modelling scenarios  16
 4.5 Design models  16
 4.6 Model validation  17
 4.7 MIKE-11 model assumptions and limitations  17
 4.8 Peer review  17
 5 Flood protection scheme  19
 5.1 Scheme history  19
 5.2 Scheme evolution  20
 5.3 River and catchment works  21
 5.4 Channel improvements  21
 5.5 Flood defences 22 
 5.6 SH25 Bridge upgrade  24
 5.6.1 Bridge design  24
 5.6.2 Bridge modelling  25
 5.6.3 Preferred SH25 bridge design 25 
 5.6.4 Constructed SH25 bridge  27
5.6.5  Reduced freeboard 27 
 5.7 Future works  27
 6 Agreed levels of service  28
 7 Operation and maintenance  29
 8 Flood hazard assessment  31
 8.1 River flood hazard classification  31
 8.2 River flood hazard map  32
 9 Residual flood risk  34
 10 Planning controls  36
 11 Scheme review 37 
 12 References 38 
  Appendix 1: Flood protection scheme design 40 
  Appendix 2: As-built survey 50 
  Appendix 3: Bridge modelling results  54
  Appendix 4: Bridge assessment  56
  Appendix 5: Bridge upgrade drawings (design) 58