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September 2010 and January 2011 Waikato Floods Review

TR 2011/39
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Report: TR 2011/39

Author: Tonkin & Taylor Ltd

About this report

In September 2010 and January 2011 significant rain fell in the Lake Taupō and greater Waikato River catchments. The resulting runoff led to significant water level rises in Lake Taupō and the requirement to manage the resulting flood flows through the Waikato River hydro cascade and into the lower Waikato system.

Lake Taupō and the Waikato River were both impacted by the flood events, and consequently the operation of the Tongariro Power Scheme (TPD) and Waikato Hydro Scheme (WHS) were important flood management considerations.

Mighty River Power and Waikato Regional Council have each prepared reports on the flood events:

  • September 2010 Flood Audit Report (Mighty River Power), dated 11 November 2010
  • January 2011 Flood Audit Report (Mighty River Power), dated 24 February 2011
  • Flood event review, September 2010 and January 2011 (Waikato Regional Council), dated 1 August 2011.

In July 2011, Tonkin & Taylor (T&T) was appointed by Waikato Regional Council to carry out an independent review of the flood event review report prepared by the council. This report presents the outcomes of that review.

The purpose of the review is to provide an independent opinion of the flood management tools, decisions and outcomes in the flood events, and in particular the consistency of these tools, decisions and outcomes with:

  • resource consents that authorise the operation of the TPD and WHS
  • Agreed Principles for High Flow Management in the Taupo Waikato Catchment
  • best practice regarding the management of hydro-electric operations during flood events
  • the reviewers' experience with regard to the management of hydro-electric operations during flood events.

Read or download the report

September 2010 and January 2011 Waikato Floods Review [PDF, 2.5 MB]

Contents
1 Introduction 1
1.1 Background 1
1.2 Purpose 1
1.3 Report structure 1
2 Flood event management within the Taupō/Waikato region 2
2.1 Introduction 2
2.2 Agreed Principles for High Flow Management 2
2.2.1 General 2
2.2.2 Objectives 3
2.2.3 Taupō-Waikato High Flow Management Plan 3
2.3 Resource consent conditions 3
2.4 WHS HFMP Objectives  4
2.5 Roles and responsibilities  5
2.5.1 Waikato Regional Council (previously as Environment Waikato)  5
2.5.2 Mighty River Power  5
2.5.3 Genesis Energy (previously as Genesis Power)  5
3 Background to the events  6
3.1 September 2010  6
3.1.1 Seasonal conditions  6
3.1.2 Event rainfall  6
3.1.3 Run off  6
3.2 January 2011  7
3.2.1 Seasonal conditions  7
3.2.2 Event rainfall  7
3.2.3 Run off  7
4 September 2010 flood management  8
4.1 Introduction  8
4.2 Tools  8
4.3 Decisions  8
4.4 Objectives and outcomes  10
5 January 2011 flood management  12
5.1 Introduction  12
5.2 Tools  12
5.3 Decisions  12
5.4 Objectives and outcomes  13
6 Technical information  16
6.1 General  16
6.2 Average Recurrence Interval  16
6.3 Simulated natural conditions  17
6.4 Previous events  18
7 Flood management best practice  19
8 Summary and conclusions  20
8.1 Summary  20
8.1.1 General  20
8.1.2 September 2010 event  20
8.1.3 January 2011 event  20
8.1.4 Outcomes  20
8.2 Conclusions 21 
9 Applicability  23
  Appendix A: NIWA La Niña forecasts