Catching litter before it reaches the sea

Published 18/08/2020

Litta traps are helping to prevent litter from going to sea in a fantastic initiative headed by NIWA.

Catching litter before it reaches the sea

By Jim McNaughton

The Body Shop in Kaiwharawhara have adopted three stormwater litta traps—traps that catch litter in stormwater sumps (drains) before it goes out to sea— for a research project run by NIWA. Once a month—before lock down—they emptied their traps across the road, analysed the contents and sent them to NIWA, who are enlisting businesses and private citizens to help investigate the effectiveness of litta traps and outlet nets for public and private use. The project is set to resume in level 1.

Body Shop Manager Kate Brooks said their trap off the main road caught almost entirely organic matter, while the other two traps on the main road— a commercial and residential area—collected a lot of rubbish. ‘Cigarette butts were surprisingly plentiful, she said. “I guess one smoker chucking a butt or two every day adds up over a month.”

Food wrapper, cans, rubber bands, and plastic fragments are also common. “We get a lot of polystyrene beads, too—one big bit breaks into thousands of pieces.”

Kate said she was keen to participate in NIWA’s study upon learning that the beach at the bottom of Kaiwharawhara Stream was the most densely plastic-polluted beach in New Zealand. “It’s a wind funnel down here. And with a commercial area being right next to the stream, rubbish that doesn’t go out with the stormwater ends up blown into the stream, and it’s a very short journey under the road to the beach.”

As well as helping with NIWA’s study, the Body shop does general litter clean-ups as well and plants trees along the stream. Kate said she’d like to give local business Wood’s Waste a shout-out for supplying a free skip during clean-ups. “The stream’s way better than it used to be. It’d be great to see lots of businesses get involved in this kind of thing.”

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Kate Brooks and Mikey Gibson of The Body Shop in Kaiwharawhara check one of their adopted 360 Stormwater litta traps.
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(L) Kaiwharawhara Stream before a
nd after tree planting(R).

People power

The Napier family adopted three stormwater traps in residential Ngaio for the study. As with Body Shop, analysis involves removing inorganic matter for sorting and classifying once a month and sending the results to NIWA—before lock down.

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(L) It’s a family affair. The Napiers at home sorting through the contents of a litta trap.
(R) Calum Napier enjoys trap adoption.


Angus Napier described the job as exercise with a bonus. “The traps are all in walking distance, so we just combine emptying the traps with a walk. It takes about five minutes to empty a trap. Sorting the litter from the organic matter back at home takes more time. It can be a bit soggy and tends to stick together.”

He said their traps aren’t in high-polluting areas. “It’s mostly organic matter. We usually collect about three times more litter on the streets while walking. There’s more on recycling days, especially if it’s windy, but people are obviously just chucking stuff out of car windows, things like fast food wrappers and cigarette butts. They don’t think it could end up in the sea.”

Hutt City Council steps up

In an exciting innovation that promises to make a significant reduction in the amount of litter going into the harbour (an estimated ten tonnes from Lower Hutt annually), Hutt City Council is looking to install litta traps across the region. 

Gordon George, Manager, Trade Waste for Hutt City Council, says that ideally the council, who are working in conjunction with NIWA and WelTec, would like to install about 500 traps. “We’ll focus on commercial areas like Jackson St, Hutt City CDB, and Naenae and Wainuiomata shops. That’s where we’re finding the most litter is being produced.”

There are a few barriers though, with the state of existing sumps and grills being one of them. ‘We need to replace cracked and broken grills first. And clean out sumps that have been repeatedly missed by cleaning trucks because of parked cars.’ Another issue is the varying shapes and sizes of the region’s sumps, some of which are not compatible with litta traps. However, Gordon doesn’t see these challenges delaying the project for too long, although the pandemic has definitely complicated things. “We’re really keen to make this happen.”  

In a further innovation, Hutt Council is also trialling an outlet net—a net over the end of a stormwater outlet pipe—in Fraser Park, and are looking at other potential outlet pipe sites with easy access for installation and regular emptying. 

The outlet net had been filling for three weeks on the day it was emptied and contained roughly one third litter. The big stuff was cans, plastic bottles and wrappers; the rest was a mix of cigarette butts, polystyrene beads and a multitude of plastic fragments.

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A three-week catch: David Fahey, Sandy Beath-Croft and Gordon George of HCC with the stormwater outlet net at Fraser Park.

Education is the key

Sandy Beath-Croft,advisor waste minimisation and sustainability for Hutt City Council, says litter traps first came to her attention in 2016 from an unexpected quarter, when Wilson School in Petone asked the council for permission to install two in Jackson Street for a student-led science project supported by Mountains to Sea.

The students went on to collect 2,680 pieces of rubbish over 12 weeks, and won an education award for science innovation. Since then, science projects for schools using litta traps have become popular. Mountains to Sea, Wellington Water and NIWA have litta traps available for loan to schools, courtesy of Stormwater 360.

Sandy thinks education is the key. “The traps are great but there are about 10 000 stormwater drains in Lower Hutt and we can only afford traps for a small proportion. The Hutt Valley acts as wind tunnel, which doesn’t help, but the root cause is human behaviour. People need to stop dropping stuff in the street and in other public places.”

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NIWA’s Dr Amanda Valoise in the field.


NIWA’s Dr Amanda Valoise, who is leading the litter capture research project, said that NIWA have installed 18 litta traps and two outlet nets in Ngaio and Kaiwharawhara, and there is growing interest.

“Porirua City Council are also getting traps as part of their wider strategy to improve the harbour. And now people have begun to adopt litta traps. I think this is a real opportunity for citizens to take responsibility.”

Dr Valoise would also like to see behaviour change around litter. And she thinks that litter is being mismanaged in our windy environment. “Too much gets away on rubbish and recycling days.” She would like to see the contents of litta traps continue to be analysed once installed by councils and businesses. “This is part of a bigger story. It would be great to combine our findings with those of Sustainable Coastlines, who are researching litter on beaches all around New Zealand. An app that showed the amount of litter being picked up in drains and on coasts in real time would be really useful. I think it would galvanise people into action. And that action would hopefully include changing the way we use plastic.”

If you would like to join NIWA’s study and adopt a litta trap, please contact Dr Valois at