The potential effects of earthquakes in the Clutha Delta area, including Balclutha and Kaitangata, have been assessed as part of Otago Regional Council’s natural hazards work.

The likelihood, potential impacts, and risks of earthquake hazards were the focus of recent independent assessments by Tonkin + Taylor Ltd.

Otago Regional Council Senior Natural Hazards Analyst Tim van Woerden says “We were seeking more information to understand the earthquake hazards occurring for events of different magnitudes, the types and severity of damage these hazards could cause, and what secondary hazards could be triggered – such as changes to flooding risk.”

One assessment specifically looked at potential vulnerability to liquefaction impacts, finding that properties on the Clutha Delta could also be affected by this in a large earthquake due to the soft sediments making up the ground.

“The risk assessment looked at three different earthquake scenarios and found in the largest case of a ‘rare’Magnitude 7 earthquake centred near the Clutha Delta, the area could be widely affected by severe ground shaking, and extensive liquefaction and ground deformation. While this scenario had the most severe impacts,

it’s also the lowest likelihood of occurring with a less than 0.04% chance of occurrence in any year.”

In the ‘likely’ scenario, with a 1% chance of occurrence in any year, light to moderate ground shaking would be experienced at the Clutha Delta and would have only minor impacts.

“These studies help to give us a better understanding of the seismic hazards and risk in the area and feeds into the Clutha Delta Natural Hazards Adaptation work which seeks to better understand future hazards, collaborate with the community to decide what’s important and build resilience.”

Earthquake scenarios and potential impact at the Clutha Delta

Background:

The Clutha Delta - a low-lying area of land of around 130 square kilometres - is exposed to a variety of natural hazards including flooding, high groundwater and drainage issues, coastal erosion and inundation, and earthquake related hazards. As these hazards change over time, the responses we rely on today to manage them may need to change to ensure resilience in the future.

Recognising this, the Otago Regional Council is working with the Clutha District Council and Emergency Management Otago and is planning to work closely with mana whenua and the community to develop the Clutha Delta Natural Hazards Adaptation Programme.

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