Watercare’s refusal to install equipment to measure overflows into the harbour from the soon-to-be-constructed Herne Bay (sewage) Tunnel has been strongly criticised by experts and this association.
The effect will be that the public won’t know when and how often sewage overflows into the harbour. This means we won’t know whether the system, that is projected to produce less than two (2) overflows p.a., from the eight Herne Bay Engineered Overflow Points, into the harbour every year by 2030, will comply with Watercare’s own brief.
No reason has been given by Watercare for refusing to install this equipment, except that it is “not in the current budget.” Why is this, we ask?
The measurement tool, a ‘weir' or small dam, is installed close to sewer overflow outfalls with sensors that detect water levels, is projected to cost about $1000 to $2000 per ‘outfall’ or overflow point.
The new sewer tunnel will retain the eight outfalls in Herne Bay – two in both Marine Parade and Sarsfield Street, and one in Herne Bay Road, Argyle Street, Sentinel Road and Hamilton Road.
So, say $20,000 for the equipment and $5000 for installation, minor in the overall multi-million-dollar cost of the project, means we won’t know if Watercare will meet its own water quality targets.
When construction of the St Marys Bay Sewerage Tunnel was completed in 2021, monitoring data, similar to what we want for Herne Bay, was installed to check whether the objective overflows into the Waitemata Harbour would reduce from an estimated 99 per year to a projected 20 per year.
Following completion of the project, Dr Ian Wallis, a world-renowned Australian Engineer, was asked to report on the success or otherwise of the project.
Because data had been collected from installed monitoring equipment as part of the project, he found that in fact discharges into the harbour actually occurred on 49 days in the 12 months following the commissioning of the tunnel.
The Herne Bay Tunnel will run some 1.5 kilometres from Marine Parade to Pt Erin and there connect to the Central Interceptor. It will collect sewage and stormwater from the St Marys Bay Tunnel and the new Herne Bay Tunnel for transmission to the Mangere Treatment Plant.
If the Central Interceptor Tunnel, that carries both sewage and stormwater, is full, as will occur at times of high rainfall, the connection from the St Marys Bay and Herne Bay Tunnels will be shut for a period.
Then the flows will discharge via the St Marys Bay Tunnel outfall. If that surcharges, then overflows from the eight outfalls located in Herne Bay will result. Without telemetry, it will not be possible to assess the results or optimise the system for maximum efficiency.
Watercare has estimated the frequency of these outflows with complex computer models. However, Dr Wallis says his experience in other cities shows a range of outcomes can occur and monitoring data at the St Marys Bay tunnel enabled potential remedial action that could be undertaken.
Herne Bay Residents Association co-chair Dirk Hudig has been actively trying to get the best quality outcomes for Herne Bay residents from sewage and stormwater projects for over 10 years. He is a member of Western Isthmus Water Quality Improvement Project Community Liaison Group.
The Project members are Watercare, Auckland Council and local resident associations.
“We have to know how this proposed new system performs,” he says. “Herne Bay currently has a combined sewer/stormwater system that overflows often.” The Herne Bay Project had predicted some ambitious outcomes, he said.
“With overflow projections of less than two annually, Watercare must install overflow measuring telemetry to keep faith with the public and maintain its public credibility.”
To this end, HBRAI has demanded that overflow telemetry be a condition of the Resource Consent for the Herne Bay Trunk Sewer Project currently being considered by Auckland City-appointed commissioners.
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Published: March 2024