Coromandel flood protection scheme service level review

TR 2018/26
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Report: TR 2018/26

Author: Anderson Aimusu

About this report

Hydrological and hydraulic models of the Coromandel Township and its catchment was developed and used to model the flood levels for Whangarahi Stream, Karaka Stream and the Golf Course Drainage for a range of different return period events, under both current and expected future climate conditions.

The modelled flood levels was then used to assess the performance of the existing stop banks and floodwalls under design storm events. The results was used for the hydrological review, it is concluded that the Coromandel scheme stop banks and floodwalls meet to their design objectives. There could still be a potential risk of flooding in the lower reach of Whangarahi Stream and on the right bank of Karaka Stream near Kapanga Road. This flooding risk is highest when there is a combined high tide level at Coromandel harbour and high overflow from Karaka Stream.

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Coromandel flood protection scheme service level review. [PDF, 2.4 MB]

Contents
1 Introduction
1.1 Background
1.2 Strategic outcomes
2 Catchment description
3 Flood hydrology
3.1 Historical records
3.2 Data Analysis
3.3 Previous analyses
3.4 Hydrological modelling
3.4.1 Model parameterisation
3.5 High intensity rainfalls
3.6 Design discharges
4 Hydraulic modelling
4.1 Boundary conditions
4.2 One-dimensional modelling
4.2.1 Channel cross sections and model network
4.2.2 Hydraulic parameters
4.2.3 Results
4.3 Coupled One/Two-dimensional modelling
4.3.1 Digital elevation data
4.3.2 Hydraulic parameters
4.3.3 Results
5 Service level assessment
5.1 Introduction
5.2 Performance grade
5.3 Results
6 Conclusion
7 Recommendations