September 2010 and January 2011 Waikato Floods Review

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.