Grahams Creek flood protection scheme design report

This design report documents how key aspects of the Grahams Creek flood protection scheme in Tairua came into being and the level of flood protection it offers this community.

Specifically the report provides an outline of the community demand for the scheme, community participation in defining the scheme parameters and levels of service, the scheme components and future requirements.

It also describes the existing residual flood risks having constructed the flood protection works, to ensure that the beneficiaries of the scheme and local communities are aware of the scheme limitations.

The technical details and data sets are covered in other technical and design reports, management reports, and project reports, which are referenced within this report.

The scheme is considered innovative and unique in a number of aspects, including rehabilitating the stream bed, self-regulating floodgate, translocation of saltmarsh and extensive riparian planting to reduce the likelihood of flooding.

The report includes the following sections:

• Catchment overview
• Hydrological assessment
• Hydraulic model parameters
• Community consultation
• Agreed service levels
• Technical design
• Operation and maintenance
• Flood hazard assessment
• Residual flood risk
• Planning controls
• Targeted rating classification
• Scheme review.

Note: The appendices have been extracted and broken into smaller parts (above) as follows:

Appendix A (part 1) - Modelled flood levels

• Figures A1 to A8 - Predicted flood levels for existing case
• Figures A9 to A16 - Predicted flood levels for current works (partial stopbank)
• Figures A17 to A24 - Predicted flood levels for proposed case (full stopbank)

Appendix A (part 2) - Modelled flood levels

• Figures A25 to A32 - Flood level profiles versus floor levels for left bank floodplain on Ocean Beach Road
• Figures A33 to A40 - Flood level profiles right bank floodplain of Grahams Creek
• Figures A41 to A46 - Flood hazard maps for existing and proposed cases for present day and climate change cases
• Figure A47 to A53 - Reduction in flood inundation times during 2%AEP (50 year ARI) event for existing and proposed works at various locations between State Highway Bridge and causeway

Appendix B - As-built drawings

Appendix C- As-builts survey

Report: TR 2018/09

Author: Ghassan Basheer