Havelock water systems vulnerable to sea level rise

Sunday, 2 June 2019

Havelock's sewage treatment plant and groundwater supplies are at risk from sea-level rise, a new report says.

The Marlborough District Council says salt water could get into the aquifer the small seaside town draws its water from.

Rising sea-levels means plans are also underway to relocate the Havelock Sewage Treatment Plant, on Queen Charlotte Drive.

The council's 'Climate Change' report - which takes a regional look at the effects climate change could have on drinking water, waste water and stormwater - shows the Havelock infrastructure is at risk.

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Researchers looked at the effect of a 300mm sea level rise over the next three decades, and 700mm by 2100.

The report was presented at a planning, finances and community meeting last month.

Council operations and maintenance engineer Stephen Rooney said after the meeting a sea level rise could increase the chance of salt water getting into the Wairau Aquifer, which feeds Havelock's fresh water supplies.

'If you raise the water pressure in the sea by rising the sea level, then that creates a pressure on the aquifer,' he said. 'If you then throw in drawing water from the aquifer from bores, you lower the pressure in the aquifer, and that potentially allows seawater to draw up into the aquifer.'

Higher temperatures caused by climate change could also encourage residents to water their gardens more, putting 'greater pressure' on the aquifer, Rooney said.

Salt water got into Havelock's drinking water about three years ago due to low water levels in the Kaituna River and a large amount of water being drawn around town.

'If you drank a glass of water, you wouldn't have noticed it, but it [the salt water indicators] showed there was a change going on in the environment,' he said.

Rooney said if the town's sewage treatment plan was not moved, a sea level rise would change the discharge flow out of the plant and could also make the times when discharge could be released shorter.

The plant, built in 1984, had two oxidisation ponds and discharged treated sewage into the Kaituna River, in Havelock.

New Zealand tidal records showed sea levels had risen an average of 1.7 millimetres a year in the last hundred years, although the National Institute of Water and Atmospheric Research (NIWA) said it had risen 3.3mm a year.

Havelock resident and mussel farmer Troy Gilbert said he was 'definitely concerned' about the potential rise.

'I work all day on the sea. I don't want to drink salty water when I come home. Fresh water is a blessing,' he said.

Kenepuru Rd resident Belinda Clancy said she had moved to the Havelock region from Christchurch about two years ago, where a sea level rise had affected her water.

'You could taste the salt. Farming also took the top level of the aquifer, which made things worse,' Clancy said.

'Summer is certainly getting hotter and the sea here is getting much warmer.'

Kenepuru Rd resident and ecologist Kim Shaw-Williams said he thought the sea level was 'definitely rising'.

'In the last 10 years, I've definitely totally noticed a difference. I'm bit of a hunter and gatherer, and I've noticed the king tide goes up higher and higher. It's freaky,' he said.

The report said more frequent and intense storms, caused by climate change, would increase the risk of sewer overflowing into urban areas through stormwater leaks.

The council would need to install larger pipes, channels and pump stations to deal with these storms and design 'detention areas' to hold back peak flows and prevent downstream flooding, the report said.

It also said increased drought frequency and duration would put a strain on water sources and water infrastructure.

One solution to managing the demand was water meters.

Metering allowed the council to gather information about how much water each household used, and where leaks were, as well as redistributing costs so people paid less if they cut back on usage.

A council spokesman said about 100 trial water meters had been installed in both Renwick and Havelock in the past few years to test the new system.

He said the switch to water meters was not expected to occur in the two towns until the 2021 financial year.