Harbour Water Quality Improvements

17 August 2009

Cleaning up our stormwater is now the focus of efforts to further improve the water quality in the harbour and around Wellington's coast.

City Council managers taking a harbour plunge

City Council managers taking a harbour plunge

We are already seeing the benefits of investing hundreds of millions of dollars in our sewerage and stormwater systems. Contamination levels in the harbour and around the South Coast have been dramatically reduced over the past 15 years.

For example, in the culvert draining to the west end of Lyall Bay beach, faecal coliform levels reached 33,000 cfu / 100ml in 1996. However readings are now down to 195 cfu / 100ml (cfu = colony-forming units - a scientific measurement of bacteria).

Similar improvements are being recorded at culverts at Evans Bay, Taranaki Street Wharf and the Overseas Passenger Terminal.

It's now safer to go swimming in the harbour and surfing at Lyall Bay, though higher levels of water contamination follow periods of rain.

It is never wise to swim in the harbour or at any urban beach for a couple of days after heavy rain.

A series of big projects have contributed to our cleaner harbour and coastline, including:

  • opening the Moa Point and Karori West wastewater treatment plants
  • constructing 20 sewage holding tanks as part of a $72 million project to eliminate sewage spills
  • building an 850,000-litre sewage tank under the Michael Fowler Centre car park to take pressure off the wastewater system during heavy rain
  • continuing removal of illegal private cross-connections that let stormwater into the sewers and vice versa.

But we're not finished yet - not until the only thing flowing into our waterways is rainwater, says Wellington City Council planning engineer Nicci Wood.

"At the moment, we don't treat stormwater in any way," she says. But that is going to have to change. "Rather than just piping it and letting it flow out into the harbour, we'll have to be a bit more creative about treating it."

A start has been made at Waitangi Park on the waterfront, where 10 percent of the stormwater draining Mt Victoria, Mt Cook and Newtown is filtered through artificial wetlands to trap pollutants before they reach the harbour.

But improving water quality needs a combined approach that includes collecting and treating sewage, preventing contamination of stormwater entering waterways by sewage or anything else, and maintaining the pipe network.

Later this month we're installing cast-iron drain lids featuring fish or crab images to remind people of the direct and untreated route that rainwater takes from the street to the harbour.

Fines for littering have also recently been increased - including the introduction of $100 fines for discarding cigarette butts in public places.

We have applied to renew our discharge consents under the Resource Management Act for all stormwater discharges to the sea. Cleaning up our waterways involves cooperation, says Nicci - and every Wellingtonian should remember that a cigarette butt dropped outside a bus stop or bar, dog poo left on the footpath, or leaking oil left on the road will end up washed down the drain and into our harbour and bays.