HEAD OF LAKE WHAKATIPU
COMMUNITY UPDATE 26 | JUNE 2023
Kia ora koutou
On May 10, we gave ORC councillors a general update on all the natural hazard work completed at the Head of Lake Whakatipu, since the last council update in June 2022. The Tonkin + Taylor Ltd report on liquefaction was included. You can read more about this below and find links to the presentation.
All of this work is leading up to our June 2024 target for the first version of a natural hazard adaptation strategy for the Head of Lake Whakatipu.
This first version will be a plan to respond to the natural hazard and climate change challenges at the Head of Lake Whakatipu, a synthesis of the assessments, technical work and community engagement to date. We are building this together with you, as well as QLDC and programme partners. The strategy will be the overarching guide of what to do, what’s most important and what’s feasible.
In the meantime, we continue to keep an eye on things. Last week, we were able to use our new flood forecast model to estimate lagoon levels ahead of forecast rainfall late last week. Find out more about the model below.
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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Social & economic impact assessment
One topic of discussion at the committee meeting was around a Social and Economic Impact Assessment. Over the past few years, we have done several technical investigations and have had a few community engagement sessions to better understand the Head of the Lake – that includes the natural hazards and risks, and also what is important about the Head of the Lake to you, the community, and our partners. The Social and Economic Impact Assessment is a key piece of information to add to the bigger picture of what we know about the Head of Lake Whakatipu and what adaptation could look like.
We recognise this is a key piece of the puzzle the community is keen to see.
We are currently scoping this work and we also know we need community input in helping figure out what the scope should be. There will be an opportunity for community input on a draft scope in the coming months. We will provide dates and more detail in next month's newsletter, if not earlier. |
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Glenorchy Flood Forecast Model
ORC has recently developed a flood forecasting model for the Glenorchy Lagoon, which allows for early warning of potential high water levels or possible flooding into Glenorchy.
How it works
The model estimates are based on forecast rainfall totals from MetService and can be used to estimate lagoon levels up to ~3 days in advance. For a forecast heavy rainfall event, we use the model to estimate the peak water level in the lagoon and get an approximation of the timing of the peak lagoon levels. The sketch figure below shows an approximate timeline for how the model can be used.
In practice
We were able to use the model last week. The ORC flood response team used the new model to estimate lagoon levels ahead of forecast rainfall and the results were very useful to inform our response for this rainfall event.
The lagoon level reached a peak of about 311.5m on Friday, 2 June and then again on Sunday, 4 June. This peak level is still about 1m below the floodbank crest level, so we could continue to monitor rainfall, river flows and lake levels as usual.
Had the forecast shown high levels, we would have notified and discussed a response with QLDC and Emergency Management Otago.
About the model
This is a newly developed model, and based on only 1-2 years of data from ORC’s new environmental monitoring sites for Rees River flows and lagoon levels. We will be testing and evaluating the model performance over the coming months, and will be able to refine the model as we continue to gather longer-duration datasets.
We are also developing our procedures for using the model and sharing results, which will include how we most effectively communicate this early-warning information with the Glenorchy community, Emergency Management Otago, and Queenstown Lakes District Council. |
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The work programme continues
We're glad to have new members on our Natural Hazards team, as we have further work planned for the remainder of this year and for next year. Here are three priorities for the adaptation programme at the Head of Lake Whakatipu in 2023 and 2024.
- Risk Assessment – what are the natural hazard risks for the main natural hazard events which may impact Glenorchy or Kinloch?
- Social and economic impact assessment – what is important now and in the future? What are the social and economic impacts of potential natural hazard events or potential adaptation approaches?
- Community engagement – what does the future look like at the Head of the Lake in the face of natural hazard challenges? What can we do to adapt, what could this look like and what options are acceptable?
In 2020, when the programme started, the ORC Natural Hazards team created this board of historical photos from the area. |
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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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