Keep it clean: NZ’s dirty water problem bigger than just cows

By Wayne Plummer, General Manager Technical Services, EnviroWaste

Two-thirds of New Zealand's rivers are too polluted for swimming and half our lakes suffer the ill effects of contamination. Pointing the finger at farmers or even the Resource Management Act won’t change things. It’s time everyone took their responsibilities more seriously.

The next time it buckets down in Auckland cast your eye seaward. At certain points along the coastline you’ll see sediment plumes take shape as giant oceangoing clouds.

The hills surrounding Weiti Bay on Auckland’s Northshore provide a good vantage point, to witness the ugly side effects of run-off from large-scale urban developments that are lashed by rain. Stand under an umbrella long enough and you’ll see a plume grow ever larger, as sediment from a local housing development is released into the northern end of the Long Bay-Okura Marine Reserve – a designated area of outstanding natural landscape and a significant ecological area.

Okura sediment plume2

Pictured:  Okura sediment plume

How is this allowed to happen you might ask, when council monitoring has shown the developer operates within its resource consent. Auckland Council says the pollution can't be stopped – it can only be managed under the Resource Management Act, which prompted one councillor to query the state of systems, both legal and technological, supposed to stop the pollution.

It’s easy to point the finger in cases like this, especially at the agriculture industry, when so many of our coastal regions and low-lying rivers and lakes are in such a perilous state.

Every industry must take a hard look at its practices if New Zealand is to reverse the harm we’re doing to our waterways. And with three-quarters of Kiwis either very or extremely concerned about the pollution of our waterways, action must go further than simply double checking activity to ensure it satisfies conditions under the Resource Management Act. We’ve got to demonstrate that we’re doing right by our environment.

Positively, the brightening spotlight on New Zealand’s dirty water problem is delivering the desired response, with many businesses now re-evaluating their approaches to water management.

Back in Auckland, the growing number of cranes that clutter the city skyline are the tell-tale signs of a construction boom in full flight. With so much of Auckland’s CBD and current development located near the coastline, adopting smarter water management practices is critical to minimising the environmental impacts of construction projects and keeping our beaches and waterways swimmable.

Excavations fill with ground water and rain water – and even seawater. With works needing to continue in all conditions, these excavations must be dewatered quickly while remaining compliant with the site’s discharge consent. Adding to the pressure of water-logged site management is the frightening spectre of being outed and shamed as the source of a filthy plume contaminating the Viaduct Basin – Auckland CBD’s major tourist hub and gateway to the Waitemata Harbour.

Conscious developers have keenly embraced smart technology to keep them compliant and ensure they do the right thing for our water systems.

At a number of these sites you’ll find EnviroWaste’s Siltbuster lamella plate clarifiers hard at work. A lamella plate clarifier is a piece of technology that uses a series of inclined plates and patented flow control systems to capture and remove suspended solids from the water.

EnviroWaste’s Siltbuster HB50 units provide water clarification for a range of applications for re-use on site, and/or discharge off-site - either to the natural watercourse or to a wastewater system.

Siltbuster dirty then clean

Pictured: Water before clarification (brown) and after (clear) – HB50

Developers I’ve spoken to praise the technology, highlighting both the compliance side of water management, and site productivity – work continues as they dewater. The baffle tanks that developers once used, no longer measure up in today’s more regulated, environmentally aware construction industry.

The volume of water processed by each HB50 unit depends on the nature of the solids suspended in the water, but generally has a recommended hydraulic capacity of 50m3/hr, or 14litres/sec.

And while that’s too small to process run-off from major rain events at large-scale developments, like Weiti, Siltbuster technology can be paired with sludge sedimentation ponds to provide polishing of the site discharge waste.  

 Intensified agriculture and dairy farmers cop the most flack for sending New Zealand’s clean green brand down the drain, but everyone needs to do better.

If Kiwi dairy farmers can spend over a billion dollars to combat river pollution and help improve the health of many our waterways, it’s time other industries stepped up their game too!