Sewer overflows blamed on heavy rain, wet wipes

Heavy rainfall is being blamed for a 47 percent increase in sewer overflows in the Bay of Plenty between 2020 and 2022.

Bay of Plenty Regional Council figures show there were 202 sewer overflows between 1 April, 2021 and 31 March, 2022. This is up from 137 overflows for the same period in 2020/2021.

Regional council regulatory services general manager Reuben Fraser said the council expected heavy rainfall had influenced the number of incidents in 2021/2022.

Provision of wastewater, stormwater and drinking water is the responsibility of city and district councils.

The council with the most incidents was Tauranga City with 72 in 2021/22 and 63 for the previous year.

Rotorua Lakes Council had 68 in 2021/22 and 37 the year before. Ōpōtiki District Council had no incidents in either year.

Whakatāne District Council was the only council to decrease their incidents, with 29 in 2021/22 and 31 the year prior.

Kawerau District Council had six in 2021/22 and one the year before that.

Western Bay of Plenty District Council (WBOPDC) had the highest percentage increase in events, jumping from five in 2020/21 to 27 in 2021/22, a 440 percent increase.

Wiped out

WBOPDC utilities operations manager EJ Wentzel said many of the Western Bay overflows come from blockages caused by people putting things down a sink or flushing them down a toilet.

This included fat or foreign objects like paper, wet wipes and sanitary pads, said Wentzel.

There were 32 sewer overflow incidents between 1 July, 2021 and 16 February, 2023, of these incidents 10 were caused by blockages from fat and six from wipes or paper, according to WBOPDC data.

Most of the 32 overflows occurred in Te Puke with 11 incidents, while there were eight in Ōmokoroa.

Wentzel said: "Another common source of overflows is from homes that have their stormwater connected to the sewer system."

"This means that rainwater goes into the sewer and can cause overflows during heavy rainfall."

Tauranga City Council (TCC) director of city waters Wally Potts said high rainfall had a role in the overflows but the majority were caused by fat or wet wipes.

"We've experienced the wettest winter, spring, and summer in the region," said Potts.

"From July 2022 to February 2023 Tauranga City has recorded 1860mm of rain or about 2.4 times the average rainfall which has put additional pressure on our stormwater networks."

"The most frequent causes [of overflows] are a build-up of fat and wet wipes, or tree roots, resulting in a full or partial block of sewer pipes," he said.

According to the TCC website two tonnes of wet wipes clog the city's pipes every week.

"Another common cause is third party strikes, where a contractor is excavating or doing some construction work and accidentally damages the sewer pipe."

Potts said overflows usually occurred at a manhole or gully trap. Around 90 percent were contained on land and cleaned up without reaching water.

Only about one in 10 ended up in a waterway that leads to the harbour or coast, he said.

The council aimed to respond to overflow incidents within 90 minutes, and usually attended within 60 minutes, said Potts.

'Only flush the three Ps'

In terms of overflow prevention, Potts said council had run a "significant" 'save our pipes from wipes' education programme asking people to dispose of wet wipes in the bin not the toilet.

"We also require our contractors undertaking public works to perform a 'Dial Before You Dig' process to minimise the likelihood of striking sewer pipes."

Western Bay of Plenty District Council also asked people to be mindful of what they flush, said Wentzel.

"We ask people to please only flush the three Ps - paper, pee and poo. That way our pipes will stay clear and we'll get far fewer sewer overflows.

"Our team also does a lot of routine maintenance including inspection of the assets, via visual, camera and remote technology.

"We also have planned maintenance including specific interventions like flushing of sewers known to be problematic. And lastly we have 24/ 7 reactive maintenance to deal with any system failures."

Fraser of BOPRC said discharges could also occur from stormwater infiltration and intrusion into the wastewater network, ageing infrastructure, overloading due to increased development and illegal connections to the system.

He said the regional council worked closely with city and district councils to reduce the risk of overflows occurring.

"There are clear expectations for maintenance and proactive management of networks as well as guidance on how to manage and respond to network overflows to ensure our communities are kept safe and damage to the environment is minimised."

Asked if there were penalties imposed for overflow incidents, Fraser replied: "If a network discharge does occur, regional council investigates the matter to consider whether enforcement is appropriate." "Taking into account the reasons for the discharge, the impact on the environment, whether or not it could have been reasonably prevented, and how the city or district council responded to the event at the time."

Fraser did not respond to the question of whether the number of overflows was acceptable.

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