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Regional flood summary: Ex-Tropical Cyclone Debbie (4-6 April), Tasman Low (11-13), and Ex-Tropical Cyclone Cook (13-14 April)

TR 2017/20

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Report: TR 2017/20

Author: Heather Craig

About this report

Following a period of intense rainfall in parts of the Waikato region during March 2017, two ex-tropical cyclones and a low pressure system (Ex-Tropical Cyclone Debbie, Tasman low, and Ex-Tropical Cyclone Cook) made landfall in New Zealand on 4 April, 11 April, and 13 April. 

The effects of these events were felt across the Waikato region with the Waihou River, Piako River and lower Waikato River systems being the worst affected. 

These three April weather events caused disruption and damage to property and infrastructure across the Waikato Region with the Hauraki Plains and Lower Waikato the worst affected with several dwellings flooded and widespread road closures.  

The purpose of this report is to summarise the rainfall events, provide rainfall and flood frequency relationships to inform additional scheme-specific performance reporting and capture the chronology of events detailed in Situation Reports issued during the events. 

Read or download the report

Regional flood summary: Ex-Tropical Cyclone Debbie (4-6 April), Tasman Low (11-13 April), and Ex-Tropical Cyclone Cook (13-14 April) [PDF, 10 MB]

Contents

1 Overview of Events
2 Comparison to previous significant flood events
3 Relevant WRC flood protection schemes
4 Regional Flood Response
5 Waikato Hydro Scheme and High Flow Management
6 Operations, observations and event impacts
7 Debriefings and lessons
8 Event magnitude summary
9 References
 

Appendix 1: Annual Exceedance Probabilities (AEP) for rainfall

 

Appendix 2: MetService watches/warnings, and WRC regional hazards advisories

 

Appendix 3: Annual Exceedance Probabilities (AEP) for instantaneous peak river flow

 

Appendix 4: River alarm levels

 

Appendix 5: Methodology memo - Flood frequency analyses for river levels and flows during

 

Appendix 6: Monthly river levels compared to March/April 2017

 

Appendix 7: Road closures and disruption