Dunedin City flooding report

The report on flooding in South Dunedin is included in an Infrastructure Services Committee report:


  1. This report follows the November 2015 report titled “Infrastructure performance during June 2015 Flood event” that focused on the water, wastewater and stormwater networks. Its purpose is to outline the known management challenges with the South Dunedin catchment, the performance of the stormwater infrastructure in South Dunedin during the June 2015 event and discuss the role of mud tanks within that.
  2. Changes in the South Dunedin catchment since the stormwater network was designed combined with operational challenges and ground water levels all contributed to the effects of the extreme rainfall event that occurred in June 2015.
  3. Staff have previously reported the contribution of the pipes and Portobello Road pump station operation to the volume of water on the surface at the peak of the flood. This modelling cannot take into account other influences such as cross catchment flows, the displacement of water by obstacles in secondary flow paths or vehicles, or the increase in hard surfaces across the catchment.
  4. Staff are therefore unable to determine the contribution to the event arising from mud tanks but have mapped mud tank conditions against known flood levels and compared this with predicted stormwater network flooding resulting from a significant rainfall event.
  5. The mapping shows correlation between known and predicted flooding. Flooding below road level would have required ground water levels to drop for it to be absorbed or to be pumped to the road where it could make its way to the system.
  6. In investigating mud tank performance, issues have been identified with the overall road maintenance regime. A number of steps, including a full review and re-tendering the road maintenance contracts, and full cleans and asset data capture of the mud tanks in South Dunedin have been taken to address these.
  7. In 2010, Council published its 3 Waters Strategy (the Strategy), which identified that stormwater flooding was a risk in some areas of the city and likely to get worse or more frequent with predicted weather pattern changes. The strategy also noted that unless appropriately managed, demographic changes and ageing infrastructure would exacerbate the situation.
  8. The strategy outlines the key technical issues, challenges and community priorities for the effective and sustainable management of Dunedin’s water infrastructure. One of the main priorities is to ensure that key service levels are maintained into the future, based on the premise that there will be no increase in the number of residential or commercial properties at risk of sewer flooding. This means that the existing levels of service across the city will be maintained.

More: http://www.dunedin.govt.nz/__data/assets/pdf_file/0003/542784/IS_20160426_AGN_294_AT.pdf

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1 Comment

  1. Zedd

     /  22nd April 2016

    walking about Stn Dn recently.. I noticed quite a few of the gutter drain grates have a green mark sprayed on them. Maybe the DCC have been unclogging them ? hope so. 🙂


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