By Chris Marshall and Dan Hutchinson

The Waikato River flows crystal clear alongside the Taupō Wastewater Treatment Plant. Photo / Dan Hutchinson

Last week’s flash flooding has raised several concerns over infrastructure in Taupō, including stormwater drains overwhelmed, and treated wastewater overflowing into the Waikato River.

The problems were the consequence of a short-lived but intense downpour in Taupō early on Friday evening.

Residents in a number of streets in the central township took videos of flooded driveways, gutters that couldn’t cope and even water pouring in window frames as well as cars on Lake Terrace coping with 100-150mm of water.

The Taupō District Council reported that the pumps at the Taupō Wastewater Treatment Plant which transfer treated wastewater to the land disposal system were unable to keep up with the significant increase in water, which resulted in some treated wastewater discharging into the Waikato River.

The overflow ran from approximately 6pm to 7pm, the council statement said, estimating that 150-200 cubic meters were discharged to the river.

“With high river flows, and the relatively short period of time that the discharge occurred over, it is expected that risks to water quality were short lived, however council staff are continuing to complete further in-river sampling to check water quality results.”

Waikato Regional Council were notified, along with relevant iwi and hapu and downstream river users, and the council said it would continue to work with them in the coming days.

The council said a full investigation would be undertaken to identify measures which could assist with managing Taupo’s wastewater system during high intensity weather events.

Tūwharetoa Māori Trust Board also released a statement in relation to the wastewater overflow.

Board chief executive Rakeipoho Taiaroa, said, while the council expected the risk to water quality to be minimal due to high river flows and the short discharge period, they remained concerned about the “ongoing impact of wastewater incidents” on the health of the waterways.

“As kaitiaki (custodians) of Taupō Waters, we have a deep responsibility to protect our awa, and any discharge raises both environmental and cultural concerns.”

The Trust Board holds title to Taupō Waters, which includes the lakebed of Lake Taupō, the Waikato Awa up to Te Toka a Tia (the Rock of Tia), Huka Falls, and the beds of various rivers and streams flowing into Taupō Moana.

“Taupō Moana and the Waikato Awa are taonga (treasures) for all New Zealanders, and we all have a role to play in their care” Taiaroa said.

“While incidents like this are sometimes unavoidable in extreme weather, we must continue to look for ways to strengthen wastewater management and better safeguard our waterways for the betterment of all communities.”

He said the board would continue working with the council, Waikato Regional Council, and other agencies to monitor the situation and advocate for efforts that prevent future wastewater incidents.

Fire crews responded to 18 flooding calls and six vegetation fires caused by lightning strikes.

Downpours caused by the intense event were very localised with most rural areas – desperate for more rain – receiving only a few millimetres.