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Managing our Environment

Frequently asked questions about flooding in South Dunedin

 

The Dunedin City Council (DCC) and ORC are jointly investigating the interaction of stormwater and groundwater in South Dunedin. DCC is developing a holistic plan to improve the management of stormwater flows and high groundwater levels. You can find out more about what DCC are doing in South Dunedin, here.

Otago Regional Council has four continuously monitored groundwater monitoring sites in South Dunedin and monitors a further 17 bores installed recently throughout the South Dunedin and Harbourside areas. You can view the latest data from these on our Water Info site. Data from the newer bores is currently being compiled by ORC but is available on request.

There is some evidence that parts of South Dunedin, especially areas of reclaimed land, are sinking gradually. Rates vary but average around 0.1cm per year and ORC is monitoring this long-term through continuous GPS measurements on Green Island. We also monitor the sea-level there to help work out how much movement is from the sea rising rather than land sinking.

The sea level relative to the land in Dunedin has gone up by about 20cm over the past 100 years. Since groundwater and sea level are connected at the coast, the groundwater level beneath South Dunedin has also risen somewhat since the area was settled by Europeans.

As much of South Dunedin has been built on reclaimed land which used to be a lagoon the groundwater levels are already very high in some areas that are of low elevation. However, the extent to which the high groundwater becomes a problem and can’t be drained away differs for different areas depending on the soil and rock type beneath.

ORC is currently working with GNS Science and others to produce an updated model showing which parts of South Dunedin will need focus first.

For more information on the NZ SeaRise project.

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