HEAD OF LAKE WHAKATIPU
COMMUNITY UPDATE 25 | MAY 2023
Kia ora koutou
We continue to build a picture of specific natural hazards in the Glenorchy township and Dart-Rees floodplain area at the Head of Lake Whakatipu (Whakatipu-Wai-Māori), and how we can adapt to them.
A new report by Tonkin + Taylor Ltd on liquefaction is the next to shed light on possible approaches to managing hazards and risks. The report will be presented to our council's Safety & Resilience Committee on Wednesday, May 10, along with a general update on all work completed since the last council update in June 2022.
Here is a head's up about the report, but we cannot share until it is uploaded as a report going to Council. On Monday, it will be uploaded in the council agenda here. It will also be available here once councillors have noted it. Meanwhile, below is some information about the report.
Also, we have provided an update on the masters research undertaken by Otago University student, Jamie MacKenzie, last year. Jamie recently joined Tim van Woerden and Jean-Luc Payan in the Natural Hazards team at ORC, as an adaptation specialist. Ann Conroy has also recently joined ORC and will be working on our adaptation work programmes with Jamie.
As always, if you have any questions or comments about reports, the work programme, or the process, please get in touch. Previous editions of the newsletter are available on the 'be involved' page (scroll down to newsletter archive) if you have missed any.
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A new report: managing liquefaction-related risk This new report by Tonkin + Taylor is an assessment on how we might mitigate or manage liquefaction if it were to occur, and alongside it, lateral spreading. Like the Damwatch Engineering Ltd report, which we shared with you last year, this report identifies a range of engineering options as well as the costs and constraints of these. It doesn't give decisions or recommendations, just weighs up the benefits and constraints of each, from robust options through to a ‘do nothing’ approach. Tonkin + Taylor were the consultants that conducted the major geotechnical investigation last year that assessed the vulnerability of the township area to liquefaction that may occur following ground shaking in an earthquake. This was presented to the community and published in June, and can be viewed here. What does this new report contain?The T+T report - Engineering approaches for managing liquefaction-related risk - is an overview of potential engineering approaches to mitigate this hazard. It asks:
- What is technically feasible?
- What are the benefits of each approach?
- What are the indicative costs and key constraints?
 Where can I read it?On Monday, the report in full will be included in the council agenda that will be here, and on Wednesday the 10th of May, following council it will be uploaded here. You can also follow the presentation and discussion of the report to the ORC Safety & Resilience Committee hereHow will it be used?This will help inform the community, our council and the Queenstown Lakes District Council on where to next. Together, we can decide how to respond to these natural hazard challenges, what will work, and what is feasible. It's the next step in developing an adaptation strategy, and continues to help build understanding of "what can we do?". Having flooding, liquefaction, lateral spreading and other data available gives us a fuller picture of the particular landscape and hazards of the area.
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Liquefaction explained
Many of us will be familiar with liquefaction, following the Christchurch earthquakes. And, if you attended our presentation in June last year to learn about the potential for liquefaction in Glenorchy from the geotechnical investigation, completed by Tonkin + Taylor, you will be even more familiar.
Liquefaction is a natural process where earthquake shaking increases the water pressure in the ground in some types of soil, resulting in temporary loss of soil strength. The severity of the liquefaction hazard depends on the strength and duration of earthquake shaking, the thickness, depth, density and type of soils and the depth of the groundwater table.
Pressure forces the sand, silt and water to move upward through cracks and out on the surface. Things sink, infrastructure is damaged and cracking is severe.
Lateral spreading
Lateral spreading is often the cause of the most severe liquefaction-related damage to land, buildings and infrastructure.
Some of the effects of liquefaction and lateral spreading are illustrated in Figure 2.1.
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Student research update
Last year, Jamie MacKenzie, a masters student from Te Iho Whenua/School of Geography at the University of Otago, undertook some research on community engagement as part of the Head of Lake Whakatipu Natural Hazards Adaptation Strategy.
Some of you may have talked to Jamie about her research or have seen her in the community observing ORC’s work around new hazard investigation findings. Jamie has now completed her masters research and will share her findings with the community at some point in the future, so stay tuned. Please note, all Jamie's interviews are confidential and anonymous.
And as she's joined the ORC’s Natural Hazards team, you may see her at the next community engagement session or out and about. Feel free to contact Jamie at jamie.mackenzie@orc.govt.nz. |
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As always, we value your feedback
This adaptation programme was initiated because complex, increasing natural hazards in the Head of Lake Whakatipu require a comprehensive management response that takes a long-term view and encompasses all types of natural hazards. This is your community, and we want to work with you to develop understanding and resilience. Check here to learn more about the whole programme.
If you have questions or need information, visit our website to see the reports, get answers to questions and read a handy summary of the June 2022 reports.
You can also contact ORC Natural Hazards Manager, Jean-Luc Payan, on 0800 474 082 or email us for more information at headofthelake@orc.govt.nz. This email will go to our Natural Hazards team, and we will provide responses to any emailed questions and facilitate answers from our consultants if needed.
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Contacts
If you have any questions or would like to get in touch with us, please email us at headofthelake@orc.govt.nz.
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