Sewage overspill issues after heavy rain targeted
A pond of fouled water at Invercargill’s Turnbull Thomson Park after two days of heavy rain in February has highlighted a problem with stormwater infiltrating and overloading parts of the city’s sewerage system.
The park has been flooded with untreated sewage in the past, notably in 2020, but the Invercargill City Council’s infrastructure manager Erin Moogan told councillors last Tuesday that this indicated a need for “isolated investment’’ in some parts of the network, rather than system-wide spending.
Part of Turnbull Thomson Park flooded when the Lindisfarne sewage pump station was overwhelmed after 38mm of rain fell on February 6, and 12mm the next day.
The council posted public warnings and notified Environment Southland, Public Health South and Te AoMārama.
“In these instances, the health and safety risk to both members of the community and animals is always present due to the nature of the water,‘’ Moogan said, prior to the council meeting.
People should strictly observe the warning signs and associated fencing, she said. Moogan told councillors work was planned in the coming years to investigate how to reduce the infiltration rate within the sewerage network.
Cr Lesley Soper sought more detail about the time frames and Moogan said she would come back to councillors with that. Turnbull Thomson Park would be the priority, she said.
To inform future decisions a project was already under way to improve the “fairly basic’’ modelling system the council had been using for its network.
Flow meters and rain gauges had been installed to monitor the network’s performance at 18 sites in Invercargill and Bluff, and the data would be used to inform understanding of stormwater infiltration at present and in cases of future development.
Cr Grant Dermody said the council faced an emerging problem with the increasing frequency of heavy rain events through climate change.
Mana whenua representative Evelyn Cook asked whether the infiltration into the sewerage system meant the city’s separate stormwater system was under-designed for how quickly water now entered it.
Moogan said the city was quite lucky to have a significantly large stormwater network – it hadn’t taken up the capacity that had been built into the system in anticipation of a larger city.