Kaihu Flood Control Scheme Investigation - Stage 3c

Barnett & MacMurray Ltd (B&M) was commissioned by Northland Regional Council (NRC) to undertake refinement of the hydrological and hydraulic models for the Kaihu River catchment, and to use the refined models to produce a preliminary plan of a flood management scheme for the Kaihu valley.

Report Table of Contents

1. Introduction
1.1 Scope of work
1.2 Background

2. Hydrology
2.1 Hydrology overview
2.2 Catchment
2.3 Rainfall
2.4 Rainfall-runoff model
2.4.1 Upper catchment calibration
2.5 Design rainfall generation
2.6 Lower catchment rainfall - runoff model
2.7 Historical floods
2.8 Design flood hydrographs

3. Hydraulic model improvements
3.1 Additional flood storage in tributary valleys
3.2 Existing river banks from new survey
3.3 Natural unmodified banks from LiDAR - procedure
3.4 Natural unmodified banks from LiDAR - comments
3.5 Additional drain outfalls from new survey
3.6 Adjustment of Frith stopbank
3.7 Adjustment of tide timing
3.8 Calibration check
3.9 Estimate of model uncertainty

4. Preliminary scheme layout
4.1 Method of developing the scheme layout
4.2 Description of proposed flood scheme
4.3 Management of flood control scheme stopbanks
4.4 New floodgates

5. Stopbanks and rough order costs

6. Benchmark simulations
6.1 Purpose
6.2 Benchmark model
6.3 Benchmark model with rail embankment removed
6.4 Benchmark flooding volumes and durations

7. Conclusions

8. Recommendations

9. References
Appendix A Figures
Appendix B Catchment Parameters
Appendix C Model files
Appendix D Boundary conditions in benchmark model
Appendix E Proposed flood management scheme layout and bank longitudinal sections