HEAD OF LAKE WAKATIPU - Community Update 15 | February 2022

Feb 17, 2022

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HEAD OF LAKE WAKATIPU

Kei aku rangatira tēnā rā koutou. Nau mai ki tēnei kawerongo. At ORC, the Covid-19 red alert level means most of our staff are working from home, except for some key workers who are out of the field to keep our communities safe.
Regardless, we are keeping an eye out for weather changes and flood risks as usual. Our responsiveness to heavy rainfall events will not be affected, so we can alert the community at the Head of the Lake area in a timely manner if necessary.
The ORC flood response team were kept busy a few weeks ago - working with Metservice to discuss weather forecasts and warnings, and monitoring of rainfalls, river flows and lake levels throughout the weather event.
While the main focus of the weather system was further north of Otago and especially along the West Coast, there was still significant rainfall in the headwaters of the Lake Wakatipu and Lake Wanaka catchments - one of our rain gauges in the Makarora area recorded a very high 24-hour rainfall total of 380mm!
During this event, the Dart River peaked at a flow of about 1,070 cumecs, and water levels at Lake Wakatipu and the Glenorchy lagoon rose by around 0.5-0.55 metres.
The ORC Environmental Monitoring team were in the Dart-Rees area last week to carry out helicopter-based flow measurements while the rivers were at higher flows. These are used for calibration of the flow estimates at the river flow monitoring stations. You can see how it works in this video.
The photos below were taken on 3 February by the ORC Environmental Monitoring team, showing the Dart River at moderate flows of about 400-450 cumecs.

Rees River flow monitoring
The new flow monitoring station for the Rees River was installed late December last year. It is located about 1km downstream from the Invincible Creek confluence. We will be working over the next few months to develop accurate flow estimates for this monitoring station. Once these are ready, the flow data will be available for you to see online and near real-time at ORC’s WaterInfo site.

River flow monitoring station installed at Rees River near Invincible Creek confluence (December 2021).

New project:
Dart-Rees floodplain hazard mitigation approaches

Starting later this February, we are bringing together a group of river expert consultants and council staff to work on a new project, aimed to brainstorm and evaluate approaches and interventions for managing the main floodplain hazards at the Head of the Lake.
Hazards such as flooding at Glenorchy, erosion and flooding at the Kinloch Road will be considered.
This group will be evaluating all possible mitigation options that were suggested by the community during our drop-in sessions last year.
The group will focus on approaches for river management options such as gravel extraction and river channel realignments, as well as engineering interventions like bunding and floodbanking.
The two key questions for this project are:

What river management approaches are viable and sustainable in the natural landscape around the Dart-Rees floodplain, and what are their potential outcomes?

What does sustainable flood protection look like in the Glenorchy area, and what level of protection is realistically achievable?

Other projects in progress

Other projects we have going on in the area include the Glenorchy liquefaction study, flood hazard assessment and alluvial fan hazard assessment.

We will let you know when the results are available to be shared, and also set up opportunities for you to give us feedback.

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