NIWA scientists unveil comprehensive map of Lake Wānaka

NIWA scientists unveil comprehensive map of Lake Wānaka

In a groundbreaking project, NIWA scientists have mapped Lake Wānaka in the lower South Island of New Zealand with exceptional detail. This initiative aims to enhance the understanding of the lake’s underwater topography and its potential seismic and tsunami hazards, following the discovery of an active fault beneath the lake three years ago. NIWA (National Institute of Water and Atmospheric Research) marine geology technician Sam Davidson shared the exciting findings, revealing that the entire lakebed and its structures can now be visualized.

“Lake Wānaka is one of the most photographed locations in the country but until now its depths have remained a mystery. We discovered some really interesting features, including complex channel systems from the rivers that feed into it. We also saw dramatic steep slopes that plummet to the deepest parts of the lake. Wānaka sits in a U-shaped valley that was carved by an ancient glacier during the last ice age over 10,000 years ago; these features and the lake’s geological history came to life in front of our eyes,” said Sam Davidson.

The team employed a multibeam echosounder, retrofitted onto a small dive vessel, to gather data over several weeks. The echosounder determined water depth by emitting sound waves that bounced off the lakebed, capturing data at a rate of 10 per second. This allowed NIWA to construct a detailed 3D model of Lake Wānaka.

Mapping project team on Lake Wānaka aboard RV Rukuwai II, with the multibeam echosounder positioned at the front of the vessel. (Image courtesy: Lana Young, NIWA)

Forecasting future changes

Dr David Plew, a NIWA hydrodynamics scientist, is leveraging the new map to investigate the lake’s water quality. “New Zealand has experienced dramatic changes in land use over the past century, which has had big impacts on our freshwater systems. Nutrient loads, the volume of water and the amount of sediment going into Lake Wānaka have all been impacted. And climate change is also affecting our lakes and will do so even more in the future,” he stated.

To forecast future changes in Lake Wānaka, NIWA is developing sophisticated computer models of the catchment and the lake itself. Prior to this, the team had been relying on charts from the 1970s.

“This new depth data that we’ve captured is more accurate and detailed. This is especially important in shallow parts of the lake such as Roys Bay and Stevensons Inlet, but also where rivers flow into the lake, because these areas have seen some of the biggest impacts and changes since the 1970s,” David Plew noted.

NIWA’s detailed mapping also aids in assessing hazards from potential seismic activity. Lake Wānaka’s location on an active fault, coupled with its steep underwater slopes, makes it susceptible to landslides that could generate tsunami-like events, threatening lakeside communities. “Now we have a clear picture of the lake’s structure, we can better inform hazard modellers and councils to better prepare for these events,” highlighted Sam Davidson.

Dr Jean-Luc Payan, Otago Regional Council’s manager of natural hazards, emphasized the value of the new data: “The new data is invaluable to inform natural hazards investigations and to understand the consequences of natural hazards events on people and infrastructure in the Lake Wānaka area.”

This significant achievement by NIWA marks a vital step towards protecting one of New Zealand’s most treasured natural environments from future natural hazards.

Close-up illustration of bathymetry data for the southern region of Lake Wānaka. (Image courtesy: Sam Davidson, NIWA)
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