Short term wastewater flooding measure planned
Dunedin (Wednesday, 4 July 2018) – The Dunedin City Council today announced that it is investigating a short-term measure which could be in place by next winter to help prevent wastewater flooding in South Dunedin.
Wastewater flooding currently occurs in South Dunedin during heavy rain, particularly in the Surrey Street/Hillside area, when the volume of water entering the wastewater system exceeds its capacity.
3 Waters Group Manager Tom Dyer says the DCC is already planning to address this issue through major projects which will see wastewater from the Kaikorai Valley catchment area – currently piped through South Dunedin to the Tahuna treatment plant – piped to Green Island for treatment instead.
However, Mr Dyer says that particular work requires a new wastewater pipe to be constructed from Kaikorai Valley to Green Island, as well as a major upgrade of the Green Island wastewater treatment plant. While planning is already underway, it will take at least eight years to fully plan, design and construct.
“The South Dunedin community has made it very clear to us that eight years is too long to wait, particularly given the potential health risks that come with wastewater flooding. We have listened to their concerns and are looking at an interim measure which could potentially be in place before next winter.”
Mr Dyer says the interim measure involves diverting a large amount of wastewater away from South Dunedin during heavy rain, by discharging it into the Kaikorai Stream.
Mr Dyer says the DCC has had some initial conversations with Kai Tahu and the Otago Regional Council about the proposal, but will need to apply for a resource consent from the ORC for it to go ahead.
Known as a wastewater overflow, this method helps avoid wastewater backing up and being discharged onto private property or roads and other places where people are likely to be.
Mr Dyer says it is important to note that wastewater overflows are heavily diluted by the amount of water in the system, and this particular overflow would be screened to prevent solid matters entering the stream. Overflows already exist on the Kaikorai Stream and in other parts of the city, but not on the same scale as the one now being looked at.
The current wastewater flooding in South Dunedin is unscreened and much of the wastewater ends up making its way into the stormwater system via mud tanks and is eventually discharged into Otago Harbour. The new proposal would send screened wastewater into the Kaikorai Stream and help prevent wastewater flooding and contamination in South Dunedin.
If the proposal went ahead, sensors would be installed in the Surrey Street/Hillside area so that the Kaikorai Valley overflow was only activated when absolutely required to help protect human health.
“This certainly isn’t intended as a permanent or ideal solution. Clearly, discharging a large amount of wastewater, albeit heavily diluted and screened, into a stream, will have an impact on the environment. However, we believe that the benefits to human health and wellbeing far outweigh the environmental impacts in this situation, until the permanent solution has been constructed,” he says.