Sewer overflows increased from 2020/21 to 2021/22. Photo / Sun Media
Heavy rainfall is being blamed for influencing a 47 per cent 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 April 1, 2021, and March 31, 2022. This was 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 the region’s city and district councils. The council with the most incidents was Tauranga City with 72 in 2021/22 and 63 the previous year.
Rotorua Lakes Council had 68 in 2021/22 and 37 the year before.
Ōpōtiki District Council had no incidents, Whakatāne District Council incidents decreased from 31 to 29 and Kawerau District Council had six in 2021/22 and one the year before.
Western Bay of Plenty District Council had five incidents in 2020/21 and 27 in 2021/22, a 440 per cent increase.
The council’s 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 July 1 2021 and February 16 2023, of which 10 were caused by fat blockages and six from wipes or paper, according to the council’s data. Te Puke had the most overflows with 11, while there were eight in Ōmokoroa.
Wentzel said homes with stormwater connected to the sewer system were a common source of overflows.
”Rainwater goes into the sewer and can cause overflows during heavy rainfall.”
Tauranga City Council 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.
He said rainfall from July last year to last month was about 2.4 times the average, which put additional pressure on 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 council’s 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 per cent were contained on land and cleaned up without reaching water. Only about one in 10 ended up in a waterway that led 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. In terms of overflow prevention, Potts said the council required its contractors undertaking public works to perform a “Dial Before You Dig” process to minimise the likelihood of striking sewer pipes.
He also said the 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.
Last year the council told the Bay of Plenty Times the campaign was believed to have contributed to a five-year downward trend in overflows, with a “significant drop” between 2019 and 2020, after the launch.
Wentzel said the Western Bay council also asked people to be “mindful of what they flush”.
”We ask people to please only flush the three P’s - paper, pee and poo. That way our pipes will stay clear and we’ll get far fewer sewer overflows.”
Its team also did routine maintenance including inspecting assets.
”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 the regional council said discharges could also occur from stormwater infiltration and intrusion into the wastewater network, ageing infrastructure and 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 said: “If a network discharge does occur, [the] regional council investigates the matter to consider whether enforcement is appropriate.”
This took 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.