State of the Gulf: Auckland Council crackdown finds majority of building sites lack sediment controls

Sediment plumes at Okura/Long Bay after heavy rain. Photo / Geoff Reid

Auckland builders are under fire after an audit found the vast majority of small sites were failing to stop sediment flushing into the city's surrounding waters.

If uncontrolled, sediment - including mud and silt - disturbed during building can be washed into the city's waterways and surrounding harbours, devastating marine ecosystems.

The State of the Gulf 2017 report highlighted sediment as one of the Hauraki Gulf's biggest issues, impacting everything from snapper stocks to shellfish beds, and increasing mud at inner-city beaches.

An Auckland Council report to be presented to the environment and community committee on July 24 found 73 per cent of 301 small sites monitored in May, mostly new houses, as non-compliant, and just 13 per cent to have adequate sediment controls in place.

A diver with their arm deep in sediment on the seafloor in the Hauraki Gulf. Photo / Supplied

At the remaining 14 per cent works had not begun.

Committee chairwoman Penny Hulse said getting sediment under control was of huge importance.

"It might not be on the top of everyone's mind, but anyone who gets out on the Waitematā or is a keen diver, like me, knows how bad the visibility gets after a bit of rain, and how muddy it is in places it didn't used to be.

"Not only are we losing precious top soil, but it is destroying marine ecosystems."

The review was the first stage of a new council initiative to reduce sediment run-off at small sites by inspecting them as soon as consents were issued, and before major earthworks began - when the biggest damage could occur.

The initiative was part of the council's Strategic Approach to Sediment programme, developed over 2018 and launched in December, to tackle sediment at its source and investigate its impacts.

It was spurred in part by the highly publicised plumes of sediment discharging into the Long Bay-Okura Marine Reserve, which the council has called a "typical occurrence" after significant rain.

Developments and building sites were required to have controls in place to prevent sediment entering waterways.

Pulse said while the larger developments were under close scrutiny, in the past smaller sites had escaped the same level of inspection.

But with some 13,500 new small sites popping up each year, covering about 600 hectares, if uncontrolled they could have a huge impact collectively.

"If you have ever been in a plane over Auckland after heavy rain you'll have seen big plumes of mud - that is what we are trying to stop happening."

Sediment plumes at Okura/Long Bay after heavy rain. Photo / Geoff Reid

The council was looking to work with, rather than against, builders and developers, Hulse said.

They had been running workshops for both builders and council staff to increase their knowledge around preventing sediment leaving a building site.

"We are finding builders and developers are very keen to get on board, many are just not sure how."

That said, some of the sites visited were "pretty chronic" and had been issued infringement notices, Hulse said.

"But we are interested in working with builders, developers and the community to raise awareness. Some might see it as another bit of red tape, but really it is about the future of the Waitematā, the Manukau, harbours."

Auckland Council's Close the Gap initiative targeting small building sites. Photo / Supplied

University of Auckland Professor Simon Thrush, who heads the Institute of Marine Science, said it was positive to see the council stepping up its compliance monitoring.

"When sediment enters the marine ecosystem, it accumulates, and causes major problems."

Thrush said people needed to be more aware about how their actions on land affected the sea.

"Any time there is a major rainfall event go and look at your favourite harbour and I can guarantee you will find it full of mud. And once it is there, it is very hard to get rid of."

Due to the small landmass, and steep rivers, when sediment entered Auckland's waterways it quickly travelled into the marine environment.

Thrush said it was important sediment was tackled from all of its sources.

"It can come from slips in native forest, on a farm, pine felling, and obviously construction. There are a lot of potential sources so we need to take a catchment-wide perspective."