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

TR 2017/20
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Report: TR 2017/20

Author: Heather Craig (with Sung Soo Koh, Jacob Williams, Dave Lovatt, & Doug Stewart)

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