HEAD OF LAKE WAKATIPU

• Buckler Burn alluvial fan
  
  Glenorchy township is situated on an alluvial fan deposited by the Buckler Burn.
  
  A physical geography team from Massey University are currently investigating the natural processes that formed Buckler Burn alluvial fan. They are looking in detail at the sedimentary deposits in drill cores from the ongoing Glenorchy liquefaction study to do this. This investigation will help us better understand the potential alluvial fan hazards of the area such as flooding and debris deposition.
  
  If the team finds any organic material that can be age-dated, they could also tell us the timing of events in the deposition of those sediments.
  
  Interestingly, a previous research project¹ has estimated that Lake Wakatipu stabilised at its current height relatively recently (in geological terms), about 500 years ago. The near-surface sediments in this area may also be relatively young.
   

  ^[1] A study by Simon Cook , Sam McColl and Tim Stahl, 2013. Surveying and Dating Post-Glacial Lake Shorelines in New Zealand. Royal Institution of Chartered surveyors (RICS).

• Glenorchy liquefaction study
  
  Investigations and analysis from the cone penetrometer tests* (CPTs) and boreholes in Oban, Coll, Islay and Mull Streets are progressing well. We are aiming to finalise the findings to share with you all in early 2022.
  
  Read more about this study of Glenorchy’s liquefaction risks here.
  
  General information about earthquakes can also be found here.
   

  *Cone penetrometer tests are used to check whether soil layers are likely to liquefy under different levels of earthquake shaking.

• Flood hazard study
  
  We are progressing the hydraulic modelling and flood hazard assessment.
  
  We have now run a model to simulate the February 2020 flood event, and the modelled floodwater coverage has matched well with observations of the flood extent in Glenorchy – a good test of the model accuracy.
  
  Next, we will model other scenarios with different river flows and lake levels, and to see what flood characteristics might look like if there was an outbreak from the Rees River.

• Rees River flow monitoring
  
  In our last newsletter, we wrote about installing a new river flow monitoring station in the Rees River near Invincible. We are planning to have this installed and operational by the end of 2021. We will let you know once it's up and running. Water flow data will be available in real-time on our WaterInfo website for anyone to access.

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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.